Biogenic volatile organic compounds (BVOCs) are intensely emitted by forests and crops into the atmosphere. They can
rapidly react with the nitrate radical (NO3) during the nighttime to form a
number of functionalized products. Among them, organic nitrates (ONs) have
been shown to behave as reservoirs of reactive nitrogen and consequently
influence the ozone budget and secondary organic aerosols (SOAs), which are
known to have a direct and indirect effect on the radiative balance and
thus on climate.
Nevertheless, BVOC + NO3 reactions remain poorly understood. Thus,
the primary purpose of this study is to furnish new kinetic and mechanistic
data for one monoterpene (C10H16), terpinolene, and one
sesquiterpene (C15H24), β-caryophyllene, using simulation
chamber experiments. These two compounds have been chosen in order to
complete the few experimental data existing in the literature. Rate
constants have been measured using both relative and absolute methods. They
have been measured to be (6.0 ± 3.8) ×10-11 and (1.8 ± 1.4) ×10-11 cm3 molec.-1 s-1 for
terpinolene and β-caryophyllene respectively. Mechanistic studies
have also been conducted in order to identify and quantify the main reaction
products. Total organic nitrates and SOA yields have been determined. Both
terpenes appear to be major ON precursors in both gas and particle phases
with formation yields of 69 % for terpinolene and 79 % for β-caryophyllene respectively. They are also major SOA precursors, with
maximum SOA yields of around 60 % for terpinolene and 90 % for β-caryophyllene. In order to support these observations, chemical analyses
of the gas-phase products were performed at the molecular scale using
a proton transfer reaction–time-of-flight–mass spectrometer (PTR-ToF-MS) and FTIR. Detected products allowed proposing chemical mechanisms
and providing explanations through peroxy and alkoxy reaction pathways.
Introduction
Human and biologic activities emit a large number of trace compounds into
the atmosphere, including volatile organic compounds (VOCs). At the global
scale, 90 % of the VOCs are emitted by biogenic activities (Guenther et al., 1995). Biogenic
VOCs (BVOCs) include isoprene (C5H8), monoterpenes
(C10H16), sesquiterpenes (C15H24) and oxygenated
compounds. Most of them are unsaturated VOCs and react rapidly with
atmospheric oxidants, leading to lifetimes below a minute for the most
reactive ones. The NO3 radical has been shown to be an efficient oxidant of
these compounds not only during the nighttime but also during the daytime under low-sunlight
conditions, e.g., below the forest canopy (Brown
and Stutz, 2012).
These reactions lead to the formation of organic nitrates (ONs) which behave
as reservoirs for reactive nitrogen by undergoing long-range transport in
the free troposphere before decomposing and releasing NOx in remote regions (Ng et al., 2017). They
therefore significantly influence the reactive nitrogenous species (NOy) and
ozone budgets in these regions (Ito et al., 2007).
Multifunctional organic nitrates are also expected to partition into
condensed phases (aerosols, droplets), and this was confirmed by field
observations which have shown that organic nitrates range from 10 % to
75 % of total organic aerosol (OA) mass (Kiendler-Scharr
et al., 2016; Lee et al., 2016; Xu et al., 2015). ONs are therefore
important components of OAs. A good understanding of the reactions of BVOCs
and NO3 is thus necessary to better assess the impact of these
processes on air quality and radiative forcing. Nevertheless, for a number
of BVOCs, this chemistry remains poorly studied.
In this study, we have investigated the reactivity of the NO3 radical with
two BVOCs, terpinolene (a monoterpene) and β-caryophyllene (a
sesquiterpene) (see Fig. 1), using simulation chambers for determining both
rate constants and mechanisms, with an experimental protocol similar to the
one used in Fouqueau et al. (2020a). Terpinolene represents 30 % of Sassafras albidum monoterpene
emissions, and the global emission is estimated to be 1.3 Tg yr-1 (Guenther et al., 2012). β-Caryophyllene
is considered to be the most emitted sesquiterpene. It is also among the
most emitted BVOCs by pine trees: it is the fifth most emitted compound by
Pinus taeda (3 % of total emissions, 47 identified species) and the second
one by Pinus virginiana (10 % of total emissions, 34 identified species),
with a global emission of 7.4 Tg yr-1. Despite these two compounds
having been detected in many tree emissions (Geron et al., 2000), their reactions with
NO3 radicals have been subject to a few studies only, and little is
known about this reactivity. Terpinolene has been subject to one absolute rate
determination (Martinez
et al., 1999) and two relative studies (Corchnoy
and Atkinson, 1990; Stewart et al., 2013). The relative value measured by Corchnoy and Atkinson (1990) is almost 50 % higher than
the other determinations. For β-caryophyllene, only one relative rate
determination was conducted. No mechanistic study has ever been published
for terpinolene to our knowledge, whereas three studies have been published for
β-caryophyllene: SOA yield was measured by Jaoui et
al. (2013), and the chemical composition of the aerosol phase was analyzed.
This study shows that β-caryophyllene + NO3 is a major source
of SOA, with production yields estimated to be 150 %. Products in the particle
phase were measured by collecting SOA on filters and by performing
derivatization followed by GC-MS analyses. Mass spectra observed for
NO3 oxidation were shown to be very different from those measured for
other oxidants, but no clear identification of the products was proposed. In
addition, this study suggests that these products contain fewer nitrogen
species than SOA from other terpenes (e.g., isoprene–NO3 system).
Fry et al. (2014) have also studied the SOA
production from β-caryophyllene + NO3. They have provided SOA
yield plots and the organic nitrate fraction in total aerosol mass.
Nevertheless, the consumption of BVOCs was very fast in this study, and this
could lead to an overestimation of SOA yields. For this reason also, some
parameters, like ON yields, were not measured. Finally, Wu
et al. (2021) studied the impact of photolysis on NO3-generated
SOA for β-caryophyllene. They measured a final SOA yield (110 %)
and provided particle-phase composition analysis, showing a major impact of
organic nitrates. Nevertheless, neither the YSOA-vs.-M0 graph nor SOA
model parameters were provided. In addition, β-caryophyllene
concentrations could not be measured by the quadrupole proton transfer reaction–mass spectrometer (PTR-MS), due to its
m/z ratio being outside the mass transmission range. New studies, both kinetic and
mechanistic, are necessary to have a better understanding of the impact of these two
compounds on air quality and radiative forcing.
Molecular representation of terpinolene (a) and β-caryophyllene (b).
Experimental section
The two different simulation chambers were used to study the reactions of
terpinolene and β-caryophyllene with NO3 radicals: the CSA
chamber and the CESAM chamber. Absolute and relative rate determinations
were conducted for both compounds. To tackle the determination of these very
fast reactions, a highly sensitive technique was required for the monitoring
of nitrate radicals. Absolute determinations were hence conducted using in situ incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS),
which was recently coupled with the CSA chamber (Fouqueau et al., 2020b). For both
compounds, mechanistic studies have also been conducted in the CESAM chamber:
total organic nitrate and SOA yields were determined, and several individual
gas-phase products have been identified. Mechanisms have been proposed for
the two compounds using this information.
Chamber facilities and analytical devices
Kinetic experiments were performed in the CSA chamber. It is a 6 m long – 977 L – Pyrex® reactor (Doussin et al.,
1997) equipped with a homogenization system allowing a mixing time below 1 min (Fouqueau et al., 2020b). This
chamber has been designed for the investigation of gas-phase chemistry and
is thus equipped with instruments dedicated to gas-phase monitoring. For
measuring organic and inorganic species in the chamber, an FTIR spectrometer
(Bruker VERTEX 80) is coupled to an in situ multiple reflection optical system.
Spectra were recorded with a resolution of 0.5 cm-1, an optical path
length of 204 m and a spectral range of 700–4000 cm-1.
During absolute kinetic experiments, an in situ IBBCEAS technique was used to
monitor NO3 radicals at the parts-per-trillion (ppt) level from its absorption at 662 nm.
This technique is described in detail in Fouqueau et al. (2020b). It allows for
the monitoring of NO3 radicals at very low concentrations (parts-per-trillion level) and exhibits a very good time resolution (10 s).
Simultaneously, it provides NO2 concentration at the parts-per-billion (ppb) level. Before
each experiment, the wavelength-dependent mirror reflectivity, R(λ), has to be very precisely and accurately determined. For this purpose, a
known amount of NO2 of several hundreds of ppb was introduced into the
chamber. To quantify both NO3 and NO2, cross sections were taken
from Orphal et al. (2003) and Vandaele et al. (1997) respectively. At NO3
maximum absorption (662.1 nm), the cross section is (2.13 ± 0.06) ×10-17 cm2 molec.-1. Thanks to the very high
reflectivity of the mirrors (99.974 % ± 0.002 %), the maximum optical
path length was calculated to be 2.5 km. This configuration leads to an
NO3 detection limit of 6 ppt for 10 s of integration time. The relative
uncertainty in NO3 concentration was estimated to be 9 %, with a
minimum absolute value of 3 ppt (Fouqueau et al., 2020b).
To study the mechanisms and the SOA formation, experiments were carried out
in the CESAM chamber (Experimental Multiphasic Atmospheric Simulation Chamber; Wang et al., 2011), which has been specifically designed to
investigate multiphase processes. Briefly, it is a 4177 L stainless-steel evacuable reactor equipped with a fan that allows for efficient mixing within approximatively 1 min (Wang et al.,
2011). Aerosol lifetimes in the CESAM chamber are up to 3 d (depending on
particle size – see the Supplement in Lamkaddam et al., 2017), which makes it well suited for
SOA studies. The chamber is equipped with dedicated analytical instruments
for gas and aerosol phases. To monitor the gas-phase composition, an in situ long-path FTIR spectrometer (Bruker Tensor 37) is coupled to the chamber. It
allows measuring spectra in the 700–4000 cm-1 spectral range with a
resolution of 0.5 cm-1 and an optical path of 174.5 m. A proton transfer reaction–time-of-flight–mass spectrometer (PTR-ToF-MS)
operating in both NO+ and H3O+ ionization modes was also
connected to the chamber. For the aerosol phase, a scanning mobility
particle sizer (SMPS) composed of a TSI Classifier model 3080 and
differential mobility analyzer (DMA) TSI model 3081 coupled to a condensation
particle counter (CPC) TSI model 3772 allows the measurement of the particle
size distribution between 20 and 880 nm. With the size distributions being measured in
number, a particle density of 1.4 g cm-3 was used to convert them
into mass distributions (Fry et
al., 2014; Draper et al., 2015; Boyd et al., 2015).
Integrated band intensities (IBIs) used in this study to quantify species of
interest using FTIR are (in cm molec.-1, logarithm
base e) as follows:
This technique was also used to measure the total organic
nitrate concentration, considering that all organic nitrates absorb at 850 cm-1 and that the intensity of this band is weakly affected by the
chemical structure of the ON. In this study, IBION (900–820 cm-1) = (9.5 ± 2.9) ×10-18 cm molec.-1
was used (Fouqueau et al., 2020a).
In addition, a high-resolution PTR-ToF-MS (Kore Series 2e, mass resolution of 4000) was
used, in both H3O+ and NO+ ionization mode. With
H3O+ ionization mode, i.e., the standard operational conditions,
organic nitrates have been shown to be subject to important fragmentation (Müller et al., 2012; Aoki et al., 2007). To
limit this, the electric field in the drift tube has been reduced following
the protocol proposed by Duncianu et al. (2017). The
instrument was also operated in NO+ ionization mode by using dry air
instead of water as ionization gas and by applying a reduced electric field
in the reactor. In this mode, ONs are mainly ionized by charge transfer and
by the formation of an adduct with NO+ and hence are detected at their
own mass M and at M+30. Hydroxynitrates are a particular case, as they are
detected at M-1, suggesting an ionization process involving a hydrogen loss.
To measure total ON yield in the aerosol phase, filter sampling was
performed during experiments. Following a protocol described by Rindelaub et al. (2015), filters were extracted in 5 mL of
CCl4 and then analyzed with FTIR. Using two standards of organic
nitrates (nitrooxypropanol and tert-butyl nitrate), they were quantified with
IBIs of 510 and 580 L mol-1 cm-2 respectively between 1264 and
1310 cm-1. The integrated absorption cross section of organic nitrates in the
liquid phase was found to be IBIONs (1264–1310 cm-1) = 557 ± 110 L mol-1 cm-2, the difference between the IBIs measured
for the two compounds being smaller than the uncertainty.
Because instruments sampling causes a pressure decrease in the chamber, pure
air is continuously injected to maintain constant pressure . The
consequence is that the mixture is subject to progressive dilution. The
dilution rate was calculated thanks to the measurement of the pure-air
injection flow. For a typical flow rate of 1.7 L min-1, the gas mixture
in the chamber is diluted by max 20 % after 3 h of experiment. All
data presented here were corrected for dilution. SOA measurements were also
corrected for particle physical wall loss, which was parametrized as a
function of the diameter of the particles and interpolated using the Lai and Nazaroff (2000) model (friction velocity u*= 3.7 cm s-1, from Lamkaddam et al., 2017). In the CESAM
chamber, the wall loss appears to be very small (in comparison to Teflon
chambers) thanks to stainless-steel walls that limit losses due to
electrostatic effects.
Chemicals
Terpinolene and β-caryophyllene were purchased from Sigma-Aldrich at
95 % and 98 % purity respectively. Synthetic air to fill the chambers
was generated using 80 % N2 from liquid nitrogen evaporation
(purity >99.995 %, H2O <5 ppm, Messer) and 20 % O2 (quality N5.0, purity >99.995 %, H2O <5 ppm, Air Liquide). NO3 radicals were generated in situ from using
the thermal dissociation of N2O5 which was first synthesized in a
vacuum line from a protocol adapted from Atkinson
et al. (1984a) and Schott and Davidson (1958) and detailed in Picquet-Varrault et al. (2009). The synthesis
proceeds in two steps: first NO3 is formed by the reaction between
O3 and NO2 (Reaction 1) and then reacts with NO2 to form
N2O5 (Reaction 2). After a purification stage by pumping the bulb
containing N2O5 for a few minutes, it is introduced into the chamber
and decomposes to form NO3 radicals (Reaction 3).
R1O3+NO2→NO3+O2R2NO3+NO2+M→N2O5+MR3N2O5+M⇆NO3+NO2+M
Kinetic study
Kinetic experiments were conducted in the CSA chamber at room temperature
and atmospheric pressure, in a mixture of N2/O2 (80/20). Both
relative and absolute rate methods were used for an accurate determination
of the rate constants. For absolute rate determination, a PTR-ToF-MS and
IBBCEAS were used to monitor BVOC and NO3 concentrations
respectively. Experiments were conducted by first introducing several
hundred ppb of NO2 into the chamber in order to determine the
reflectivity of the IBBCEAS mirrors. Then, the BVOC was injected and left in
the dark for approximatively 1 h. This allows checking for eventual wall
loss or reaction with NO2. No significant loss was observed. In order
to limit SOA formation, which would strongly reduce the IBBCEAS signal due to
light absorption and/or scattering and mirror soiling by particles, low BVOC mixing
ratios have been used (between 15 and 90 ppb). In addition, the mirrors were
flushed with nitrogen to protect them from particle deposition. Finally,
NO3 was generated in situ (see Sect. 2.1) by stepwise injections of
N2O5, and measurements were performed with a time resolution of 10 s in order to allow monitoring fast decay of reactants. Several
stepwise injections of N2O5 were made until the complete BVOC
consumption.
Considering the following reaction,
BVOC+NO3→products,
the second-order kinetic equation is obtained:
-dBVOCdt=kBVOC[BVOC][NO3].
For small time intervals, such as the time resolution used in this study, it
can be approximated as
-Δ[BVOC]=kBVOC[BVOC][NO3]Δt,
where -Δ[BVOC] is the decay of the BVOC during the Δt time
interval and BVOC and [NO3] are averaged
concentrations during this interval. kBVOC is obtained by plotting -Δ[BVOC] vs. [BVOC] × [NO3] ×Δt. It should be
mentioned that the determination of the rate constant is thus not affected
by losses of NO3 due to reaction with other species (products, RO2
radicals, etc.) as the rate constant is not deduced from the NO3
consumption rate but from the BVOC one. The uncertainty in kBVOC was
taken as twice the standard deviation of the slope.
For relative rate determination, PTR-ToF-MS and FTIR techniques were used to
monitor the BVOC decay relatively to a reference compound. As with absolute
rate experiments, the organic reactants were left in the dark for 1 h
prior to the N2O5 injection. By assuming that consumption by
NO3 is the only fate of the studied BVOC and the reference compound and that these compounds are not a product of both of the reactions, the
following equation can be shown (Atkinson, 1986):
lnBVOCt0BVOCt=kBVOCkRef.lnRef.t0Ref.t,
where BVOCt0 and Ref.t0 are BVOC and reference
concentrations at time t0 (which correspond to the moment before the
beginning of the oxidation), BVOCt and Ref.t are the concentrations at t time, and
kBVOC and kRef. are the rate
constants with NO3.
In this work, 2,3-dimethyl-2-butene was used as reference compound because
of its well-known rate constant with NO3 radicals. In absence of a
recommendation by IUPAC, the value recommended by Calvert
et al. (2015) and by McGillen et al. (2020) was used. However, the uncertainty proposed by these recommendations is
very high (150 %) despite the fact that experimental determinations are in
good agreement. So, uncertainty was reevaluated and calculated as the mean
value of the determinations available in the literature (Berndt
et al., 1998; Benter et al., 1992; Lancar et al., 1991; Rahman et al., 1988;
Atkinson et al., 1988, 1984a, b). The obtained value is
k2,3-dimethyl-2-butene= (5.7 ± 1.7) ×10-11 cm3 molec.-1 s-1. The same value and corresponding
uncertainty were used by Newland et
al. (2022). Finally, the uncertainty in kBVOC was calculated by
considering the relative uncertainty corresponding to the statistical error
in the linear regression (2σ) and the error in the reference rate
constant.
Mechanistic study
A mechanistic study was conducted in the CESAM chamber at room temperature and
atmospheric pressure, in a mixture of N2/O2 (80/20). Experiments
were typically conducted by first introducing the BVOC into the chamber and
leaving it in the dark for approximatively 1 h to estimate possible
wall and/or dark losses. No significant wall loss was observed for both studied
BVOCs (kd<10-7 s-1). Then N2O5 was
introduced by slow continuous injections as this method has been observed to
be more efficient than stepwise injections in slowing down the oxidation and
thus better controlling the SOA formation. A PTR-ToF-MS and FTIR spectrometer
were used to monitor both BVOC and gas-phase products. In some experiments,
two PTR-ToF-MSs were used in order to detect gas-phase products in both
NO+ and H3O+ ionization modes simultaneously. If using two
instruments was not possible, experiments were duplicated. An SMPS was used to
monitor the SOA production. Because of the lack of standards, quantification
of gas-phase products measured by the PTR-ToF-MS was not possible. In order to
measure SOA yields under low aerosol content, no seed particles were
introduced into the chamber. Filter sampling was performed for experiments
for which the concentration of the precursor was up to 150 ppb. It started when
the precursor had completely reacted and lasted for 3 to 6 h. To avoid
the condensation of gas-phase products on the filter, a charcoal denuder was
used.
When products could be quantified by FTIR, their formation yields were
calculated by plotting their molecular concentration against the reacted
BVOC molecular concentration and by calculating the slope at the origin. To
calculate the total organic nitrate yields in the SOA phase, the final organic
nitrate concentration measured on the filters was divided by the total
reacted BVOC concentration. Uncertainties in formation yields were
calculated as the sum of the relative uncertainties in the product and the
BVOC cross sections and twice the standard deviation of the linear
regression. Organic nitrates have been measured in both gas and particle
phases. Consequently, a total organic nitrate yield has been calculated,
being the addition of these two yields. Their uncertainties were calculated
as the sum of the relative uncertainties in gas- and particle-phase yields.
SOA yield is defined as the ratio between the produced SOA mass
concentration, M0, and the reacted BVOC mass concentration, ΔBVOC. It was calculated for each data point and after the total consumption
of the BVOC for all experiments, providing time-dependent and overall SOA
yields. Uncertainties in SOA yields were calculated as the sum of the
relative errors in VOC concentrations measured by FTIR and the SOA
concentration measured by the SMPS. Knowing both the organic nitrate yield in the
particle phase and the total SOA yield, the ratio YONp, mass/ YSOA, mass has been calculated. Uncertainties were calculated as the sum of relative errors in YONp and YSOA.
SOA yields were plotted against the organic aerosol mass, and a fit was applied
using a two-product model described by Odum et
al. (1996):
Y=M0α1Kp,11+Kp,1M0+α2Kp,21+Kp,2M0,
where α1 and α2 and Kp,1 and Kp,2 are
stoichiometric factors and partitioning coefficients (in m3µg-1) of the two hypothetical products respectively. It was expected
that SOA equilibrium would be reached in small time steps because of the slow
injections of N2O5; thus time-dependent yields have been used.
Hence, yields for small aerosol content have also been obtained.
In order to assess their contribution to SOA formation, vapor pressures
Pvap have been evaluated using the SIMPOL.1 method (Pankow
and Asher, 2008) via the GECKO-A website (http://geckoa.lisa.u-pec.fr, last
access: 5 March 2021). In order to estimate the fraction of a product
i in the condensed phase ξaeri, Raoult's law has been
used (Valorso et al., 2011):
ξaeri=Ni,aerNi,aer+Ni,gas=11+Maer‾γiPivapCaerRT×106,
where Ni,gas and
Ni,aer are respectively the gas- and
particle-phase concentrations (in molecules cm-3) of the product i,
Maer‾ the SOA species mean molecular weight (g mol-1), Caer is the total SOA mass concentration
(µg m-3), R the gas constant (atm m3 K-1 mol-1),
T the temperature (K), Pivap the vapor pressure and
γi the product i activity coefficient
(γi=1 was used in this study). Here,
Maer‾ has been estimated to be the mean molecular
weight of detected low-volatility products.
The calculation of ξaeri depends strongly on the estimation of
Pvap. It was shown by Pankow
and Asher (2008) that SIMPOL.1 technique predicts it with an uncertainty
between 50 % and 60 % for Pvap<10-6 atm. The uncertainty can reach 80 % for Pvap=10-10 atm. ξaeri can only be used as a guide, because it is
associated with a high uncertainty. ξaeri has also be compared to
the partitioning coefficients Kp used in Eq. (4):
Kp=Ni,aerNi,gas×1Caer=ξaeri1-ξaeri×1Caer
Kinetic results
All experiments and their conditions are presented in Table 1. Both of the
compounds were subject to absolute and relative rate determinations. For
each method, between two and four experiments were conducted.
Experimental conditions of kinetic experiments. [BVOC]i and
[Ref.]i are the initial mixing ratios of the BVOC and of the reference
compound. For [N2O5], the number of punctual injections is
indicated in parentheses. T is the mean temperature inside the simulation
chamber during the experiment.
Kinetic results obtained by the relative rate method are plotted in Fig. 2.
They present good linear tendencies and are in good agreement whatever the
analytical technique used. For both individual data sets obtained by
a PTR-ToF-MS and FTIR, linear regressions have been first performed
separately. The results being in good agreement, a global linear regression
was applied to all the data, leading to kterpinolene= (6.0 ± 2.5) ×10-11 cm3 molec.-1 s-1 and kβ-caryophyllene= (1.4 ± 0.7) ×10-11 cm3 molec.-1 s-1.
Relative kinetic plots measured by FTIR (triangle marks) and
a PTR-ToF-MS (square marks) for terpinolene (a) and β-caryophyllene (b).
Absolute kinetic plots are shown in Fig. 3. Experimental points are rather
scattered, and this can be explained by the low integration time used for
PTR-ToF-MS and IBBCEAS measurements. As a consequence, rate constants are
subject to relatively high uncertainties. Rate constants measured by the
absolute rate method are (4.9 ± 1.4) ×10-11 cm3 molec.-1 s-1 for terpinolene and (2.0 ± 0.6) ×10-11 cm3 molec.-1 s-1 for β-caryophyllene.
Absolute kinetic plots for terpinolene (a) and β-caryophyllene (b).
The values measured by both the relative and the absolute methods are
compared to those already published in the literature in Table 2. In order
to compare our values with literature data, the relative rate from Corchnoy and Atkinson (1990) has been recalculated using the
same value for the reference rate constant (see Sect. 2.3). The value
obtained by Stewart
et al. (2013) with limonene as the reference compound was also recalculated
using the latest IUPAC recommendation: (1.2 ± 0.4) ×10-11 cm3 molec.-1 s-1. Finally, the rate constant
provided by Shu and Atkinson (1995) was recalculated using the
value (9.6 ± 1.6) ×10-11 cm3 molec.-1 s-1 for 2-methyl-2-butene. This value has been obtained by averaging
all determinations published in the literature. The total uncertainties
presented in this table for relative rate determinations are the sum of the
statistical errors provided by the authors and the errors in the reference
rate constants.
Rate constants for the
NO3-initiated oxidation of terpinolene and β-caryophyllene: results from this study and comparison with the
literature. Rate constants of α- and γ-terpinene found by Fouqueau et al. (2020a) are also shown. The results of our study are in bold.
BVOCk (cm3 molec.-1 s-1)(kCOVB/kref)Study (method)Terpinolene(4.9±1.4)×10-11This study (ARa)(7.0±2.5)×10-11(1.2±0.1)This study (RRb: 2,3-dimethyl-2-butene)(8.5 ± 3.4) ×10-11(1.7 ± 0.1)Corchnoy and Atkinson (1990) (RRb: 2,3-dimethyl-2-butene)(5.2 ± 0.9) ×10-11Martinez et al. (1999) (ARa)(6.2 ± 3.0) ×10-11Stewart et al. (2013) (RRb: limonene)6.6 ×10-11(5.1 ± 0.4)Estimated with SAR (Kerdouci et al., 2014)β-Caryophyllene(2.0±0.6)×10-11This study (ARa)(1.5±0.7)×10-11(0.27±0.04)This study (RRb: 2,3-dimethyl-2-butene)(2.0 ± 0.7) ×10-11(2.1 ± 0.4)Shu and Atkinson (1995) (RRb: 2-methyl-2-butene)2.1 ×10-11Estimated with SAR (Kerdouci et al., 2014)γ-Terpinene(2.9 ± 1.1) ×10-11Fouqueau et al. (2020a)α-Terpinene(1.2 ± 0.3) ×10-10Fouqueau et al. (2020a)
a Absolute rate determination. b Relative rate determination.
For terpinolene, the absolute and relative determinations obtained in this
work are in good agreement. They also appear to be in good agreement with
the values provided by previous studies, within uncertainties. Nevertheless,
when considering the kCOVB/kref values obtained in this work and
by Corchnoy and Atkinson (1990) (both were using the same
reference compound), it appears that the two relative rate determinations
are not in agreement. The value obtained by Corchnoy and
Atkinson (1990) is 40 % higher than that in our study. No explanation has been
found for this difference, but it can be seen that the value of Corchnoy and Atkinson (1990) is higher than every other value
in the literature. Our result thus confirms the lower values found by
previous studies. For β-caryophyllene, the absolute and relative
determinations obtained in this work are also in good agreement. These
determinations have been compared to the only determination previously
published by Shu and Atkinson (1995). A good agreement can be
observed, whatever the method used. Our study provides the first absolute
rate determination for β-caryophyllene. Our data were also compared
to estimated rate constants using the structure–activity relationship (SAR)
developed by Kerdouci et al. (2014). Experimental and
estimated rate constants show a good agreement.
The terpinolene rate constant can be compared to the values found by Fouqueau et al. (2020a) for α-terpinene and γ-terpinene and is shown in Table 2.
They indeed have very similar structures, only differing by the position of
the double bonds. α-Terpinene and γ-terpinene have endocyclic double
bonds (conjugated and not conjugated respectively), whereas terpinolene has
one endocyclic and one exocyclic double bond. α-Terpinene appears
to be much more reactive than γ-terpinene due to the conjugation of
double bonds which leads to a stabilization of the transition state by
resonance. Here, terpinolene is almost twice more reactive than γ-terpinene, and this can be explained by the substitution of the exocyclic
double bond which stabilizes the adduct. In addition, terpinolene, which has
non-conjugated C=C bonds, is less reactive than α-terpinene.
Mechanistic results
Seven mechanistic experiments were conducted in the CESAM chamber for
terpinolene and nine for β-caryophyllene. During experiments, the
formation of gas-phase products and SOA was monitored. Table 3 presents
experimental conditions together with organic nitrates and SOA yields that
were measured. As an example, reactant and product time profiles
(corrected for dilution) are presented in Fig. 4 for the experiment on 18 December 2017 on terpinolene. In the first minutes following N2O5
injection (marked by the red area), a competition occurs between the
reactivity of NO3 on the BVOC and its wall loss through N2O5
hydrolysis. In the beginning of the experiment, mainly nitric acid is thus
formed by N2O5 hydrolysis on lines and chamber walls. Then, the
BVOC starts to be oxidized with the weakening of the hydrolysis reaction.
Because small quantities of N2O5 were introduced continuously in
order to ensure a progressive oxidation of the BVOC, N2O5
concentration remains below the detection limit as long as the BVOC is not
totally consumed (around 25 min here). The formation of large amounts of
organic nitrates and SOA is observed: for an initial terpinolene mixing
ratio of 180 ppb, up to 70 ppb of total organic nitrates and 400 µg m-3 of aerosol are formed. Figure 4 also shows the aerosol size
distribution. It can be seen that particles have mean diameters around
300–400 nm. PTR-ToF-MS signal (m/z) time profiles are presented in Fig. S1 in the Supplement and are discussed later with their identification.
Experimental conditions, ONs and SOA yields for mechanistic
experiments conducted in the CESAM chamber. The use of an instrument is shown by
an “x” and the non-use by a dash.
* For all experiments, the BVOC was totally consumed.
Dilution-corrected time-dependent concentration of gaseous
species, aerosol mass, SOA size distribution during a typical experiment of
NO3-initiated oxidation of terpinolene (18 December 2017). The hatched red area
corresponds to the N2O5 injection period. (a) Terpinolene,
N2O5, NO2, HNO3, acetone and total ONs from FTIR and SOA
mass concentration from the SMPS; (b) SOA size distribution in mass
concentration from the SMPS. The time zone of the time scale is UTC+1.
For β-caryophyllene, only two experiments could be used to determine
the SOA yields. Indeed, except for experiments conducted in December 2017,
very large amounts of SOA were formed (between 500 µg m-3 and 1 mg m-3), and the upper part of the size distribution fell out of the SMPS
range, affecting the relevance of the mass evaluation from SMPS measurement.
SOA yields
Figure 5 shows time-dependent and overall SOA yields (YSOA) as a
function of the aerosol mass (M0) for both terpinolene and β-caryophyllene. As explained before (see Sect. 2.4), a two-product model
defined by Odum et al. (1996) has been applied
for the two compounds. Final yields obtained for terpinolene can reach 60 %, whereas they are between 50 % and 90 % for β-caryophyllene.
These results demonstrate both of the compounds are very efficient SOA
precursors.
SOA yield as a function of the organic aerosol mass concentration
measured for terpinolene (a) and for β-caryophyllene (b). Final
yields (circle marks) are shown with uncertainties. Data were fitted with a
two-product model (black curve). For β-caryophyllene, literature
values are presented by squared marks.
For terpinolene, our study provides the first determination of SOA yields.
Figure 5 shows that fitted plots are well constrained for small aerosol
contents (below 50 µg m-3) thanks to the high number of
experimental points in this area. This is a consequence of the slow
injection of N2O5, which allows progressive BVOC oxidation.
Fitted parameters have been found to be α1=0.6 and Kp,1=6.7×10-3 m3µg-1 and α2=3×10-3; Kp,2=3.5×10-1 m3µg-1. The very low stoichiometric factor α2 indicates that
the second class of products is negligible, so the particle-phase products
can be simulated with only one family of the same volatility. One can estimate
the uncertainties in fitting parameters by looking at the fit sensitivity.
It appears to be very sensitive to α (with an associated error
estimated to be 5 %) and less so to Kp (with an error estimated to be 50 %). For an aerosol mass concentration typical of a biogenic SOA-affected
environment of 10 µg m-3 (Slade et al., 2017), an SOA yield of 5 % has been measured for terpinolene. For higher aerosol mass loading,
which can be observed in polluted atmospheres (between 500 and 1000 µg m-3), yield reaches 50 %–60 %.
For β-caryophyllene, a high dispersion is observed between the data
from the two experiments, for low aerosol mass loadings that correspond to
the first stages of the oxidation. For the experiment on 22 December 2017, an
“unusual” profile is observed in the sense that the SOA yield decreases
with the increasing M0. This suggests that, despite a slow injection of
N2O5, the oxidation of the β-caryophyllene was too fast in
comparison to the mixing time, leading to a locally high concentration of
semi-volatile species and, therefore, to an overestimation of the SOA yield.
After a few minutes, the SOA yield decreases and is then in good agreement
with those measured for the experiment on 15 December 2017, suggesting that
semi-volatile species are better mixed in the reactor and therefore SOA
yields are more accurate. The Odum fitting parameters obtained from these
two experiments are α1=0.5 and Kp,1=4.1×10-1 m3µg-1 and α2=3.8×10-3 and Kp,2=5×10-1 m3µg-1. As with
terpinolene, the high value of α1 and low α2
indicate that one class of products, having a high partitioning coefficient
(Kp.1), contributes mainly to the SOA formation. These results also show
that β-caryophyllene is a very efficient SOA precursor with a yield
close to 40 % at 10 µg m-3, which can reach almost 60 %
for higher aerosol mass loading. Nevertheless, due to the experimental
problems mentioned above, this model is not well constrained for low aerosol
mass loading (<100µg m-3), and these results have to be
taken with caution. Three studies have been previously conducted on the SOA
production from β-caryophyllene. First, Jaoui et al. (2013) measured SOA yields in a simulation chamber. In this study, final
aerosol yield has been provided without indication of the aerosol mass
loading, thus preventing fitting data by the Odum model. Yields were
shown to range between 91 % and 146 %. The Fry
et al. (2014) study has provided SOA yields curves and ON yields in the particle
phase. This study has been conducted with high and low BVOC concentrations
(3 and 109 ppb respectively). Since experiments were carried out by
introducing the oxidant into the chamber prior to the BVOC, the latter
began to react immediately, preventing measurement of its initial
concentration. The consumption of the BVOC had therefore to be estimated. In
a similar way to our study, the authors have observed differences between
high- and low-concentration mass yield curves, suggesting that the experiments
differ in more than simply the total aerosol mass loading. They measured
higher yields for high-concentration experiments than for low-concentration
experiments (for the same aerosol mass loading). The authors recommend
preferentially using data obtained for low-concentration experiments considering
that due to the slower reaction, the ΔVOC is better constrained for
longer periods and the mixing timescale is faster relative to reactions,
resulting in more precise yield curves. However, even for these low-concentration experiments, the yields obtained (around 80 %) are much
higher than those measured in our study. Such disagreement could be
explained by the fact that ΔVOC is not precisely measured in the Fry et al. (2014) study. Another possible
explanation provided by the authors that could explain the difference
between high- and low-concentration experiments and also the disagreement
between their results and our study may lie in the differences in the RO2
radical fate. RO2 radicals can indeed react following several pathways,
in particular with NO3 or with other RO2 radicals, and products
resulting from these two reactions differ. For example, RO2+ RO2
reactions can produce hydroxynitrates, which have low volatility and can
thus participate to SOA formation (see discussion in Sect. 4.3). Finally, Wu
et al. (2021) studied the photolytically induced aging of NO3-initiated
SOA. In order to fulfill this aim, they first generated SOA by reacting
β-caryophyllene and NO3. One experiment was conducted with 50 ppb of precursor, and a final SOA yield of 110 % was calculated. Two
issues are pointed out: firstly, they could not monitor β-caryophyllene with a quadrupole PTR-MS because its m/z ratio was out of
the range for quantitative measurement. The method used to calculate its
concentration is then not explained, but it is probably associated with a
larger uncertainty. Secondly, a concentration of more than 200 ppb of
N2O5 is injected during approx. 10 s. As explained before, this can
lead to an SOA yield overestimation and thus explain the observed
differences. Nevertheless, the mean diameter of the size distribution measured
in the study is between 229 and 266 nm, which is in good agreement with the
ones measured here (between 225 and 246 nm at the end of the oxidation).
The Wu et al. (2021) study showed no evaporation of SOA during dark aging, which agrees
with the fact that SOA concentrations are stable here, after the oxidation.
In conclusion, this discussion illustrates well how SOA yields may be
affected by a number of parameters and how comparisons are difficult to
interpret.
Organic nitrate yields
The total ON yields have been measured in the gas phase (YONg). Their
concentrations have been plotted against the consumption of the BVOC for both of
the studied compounds in Fig. 6. The plots show a good linearity, and the
slope at the origin is different from zero. This indicates that (i) organic
nitrates are primary products and (ii) if they themselves react with NO3
by addition to the other C=C bond, they produce secondary organic
nitrates, so the total ON yield is constant during the course of the
experiments as FTIR measurement cannot differentiate primary and secondary
organic nitrates. Previous studies performed in the CESAM chamber have reported
that ONs may be subject to wall losses, through absorption on the stainless-steel walls (Suarez-Bertoa
et al., 2012; Picquet-Varrault et al., 2020). Loss rates have been found to
be between 0.5 and 2 ×10-5 s-1. In this study, because
ON yields were calculated for a short period (max 1 h), wall losses at
this timescale are estimated to be less than 10 %. This is confirmed by
the good linearity of the plots.
Gas-phase organic nitrate production vs. loss of terpinolene (a) and
of β-caryophyllene (b).
Molar YONg values were found to be 47 % ± 10 % for terpinolene and 43 % ± 10 % for β-caryophyllene. These yields are in good
agreement with previous studies performed for other BVOCs and show that
ONs are major products of BVOC + NO3 reactions. ON yields measured
for isoprene and monoterpenes are indeed higher than 30 %. For example,
limonene ON yields vary between 30 % and 72 % (Fry
et al., 2014; Hallquist et al., 1999; Spittler et al., 2006) and β-pinene between 40 % and 74 % (Fry et al.,
2014; Hallquist et al., 1999; Boyd et al., 2015). For α- and γ-terpinene (Fouqueau et
al., 2020a) very close yields (47 % and 44 % respectively) have been
measured. The only exception is α-pinene, for which yields vary
between 10 % and 30 % (Fry
et al., 2014; Hallquist et al., 1999; Spittler et al., 2006). Its main
product is indeed an aldehyde, with a high vapor pressure, that does not
contribute to the SOA phase.
Organic nitrates may partition between gas and aerosol phases. Hence, yields
of total organic nitrates in the particle phase (YONp) have been
determined using FTIR analyses of the collected filters. Results are shown
in Table 3. For terpinolene, molar yields range between 7 % and 23 %. The
variability in these yields can be explained by the fact that, as SOA
yields, they depend on the reacted BVOC concentration. They are thus
probably overestimated in comparison with real atmospheric conditions.
Indeed, for high-concentration experiments (∼350 ppb), yields
are around 20 %, whereas they are around 7 % for the low-concentration
experiments (∼180 ppb). For β-caryophyllene, YONp values
range between 21 % and 25 % and appear to be less subject to variability.
In order to evaluate the fraction of organic nitrates in SOA, YONp values have
been compared to SOA yields. For this comparison, both yields have to be
expressed in mass. To do so, a unique molecular weight which is
representative of the expected oxidation products has been considered: for
terpinolene, a hydroxynitrate (C10H17O4N) having a molecular
weight of 215 g mol-1 has been chosen. For β-caryophyllene, the
same type of compound has been chosen (C15H25NO3), with a
molecular weight of 283 g mol-1. Both compounds were detected as
oxidation products by PTR-ToF-MS. It is clear that this assumption generates
a large error in ON mass yield, particularly if other products are formed
with higher molecular weights (e.g., by polymerization in condensed phase).
Nevertheless, as oxidation products were not quantified individually, this
method is the only way to estimate the contribution of ONs to the aerosol
phase. The ratio YONp, mass/YSOA, mass values are also shown in Table 3. From these results, it is estimated that organic nitrates represent ∼50 % of the SOA for terpinolene and ∼80 % for β-caryophyllene and are therefore major components of the SOA produced by
BVOC + NO3 reaction. It should be noted that if higher-molecular-weight products were formed, these ratios would be even greater. The value
obtained for β-caryophyllene is in very good agreement with the ratio
of 80 % provided by Fry et al. (2014).
These results are also in good agreement with field studies (Kiendler-Scharr
et al., 2016; Ng et al., 2017) which have observed that organic nitrates
are major components of organic aerosols, with a proportion that can reach
almost 80 %. Even if organic nitrates can be produced by other reactions,
an enhancement of organic nitrates in SOA has been observed by several
studies in regions impacted by the NO3 radical during the night (Gómez-González
et al., 2008; Hao et al., 2014; Iinuma et al., 2007) and also in forest
regions affected by urban air masses (Hao
et al., 2014). This result thus confirms the major contribution of organic
nitrates in SOA formation.
Acetone production vs. loss of terpinolene.
Products at molecular scale and mechanisms
To propose explanations for the measured yields, mechanisms have been built,
using the molecular-scale PTR-ToF-MS identification of gas-phase products.
By using two ionization modes (i.e., H3O+ and NO+), a double
identification of the molecules was possible. Detected signals in both
ionization modes and corresponding raw formulae are summarized in Table 4.
Products with molecular weights of 58, 142 and 168 g mol-1 for
terpinolene have been detected with high intensities. For β-caryophyllene, the main signals were measured for products having molecular
weights of 221 and 236 g mol-1. In Table 4, intensities are shown
following this logic: the one or two most intense peak are marked
“+++” and are usually at least 1 order of magnitude higher than
the other ones. Peaks that are more intense than 10 counts are marked
“++”, and the other ones are marked “+”. Many of the products which
were detected are nitrogenous species, which is in good agreement with the
measurement of high organic nitrate yields. Mechanisms have been proposed
in Fig. 8 for terpinolene and in Fig. 9 for β-caryophyllene. Time
profiles of PTR-ToF-MS signals (see Fig. S1 in the Supplement) were also used to determine
whether the products are primary or secondary ones. First-generation
products are framed in blue and second-generation ones in red.
Products detected for terpinolene (a) and β-caryophyllene (b) with PTR-ToF-MS
H3O+ and NO+ ionization modes: formulae and molar
masses, detected masses, ionization processes (H+:
proton adduct; NO+: NO+
adduct; CT: charge transfer; PL: proton loss), peak intensity, and
comportment.
Proposed mechanism for terpinolene. First-generation products are
squared in blue and second-generation ones in red. Alkoxy fragmentation
products are squared according to the location of the fragmentation.
Molecular weight, vapor pressures and the gas–particle partition are shown
next to the molecules.
Proposed mechanism for β-caryophyllene. First-generation
products are squared in blue and second-generation ones in red. Alkoxy
fragmentation products are squared according to the location of the
fragmentation. Molecular weight, vapor pressures and the gas–particle
partition are shown next to the molecules.
In addition, for experiments on terpinolene, acetone was detected by FTIR
and its formation yield has been measured. Figure 7 shows the concentration of
acetone plotted against the consumption of terpinolene. Every experiments
shows similar and linear tendencies, within uncertainties. Acetone appears
to be a primary product, with a production yield of 23 % ± 5 %.
Terpinolene is thus a major precursor of acetone.
Terpinolene oxidation scheme
The NO3 radical reacts with terpinolene by addition onto one of the two
double bonds (H-atom abstraction is considered negligible), each addition
leading to the formation of two possible nitrooxy-alkyl radicals. According
to the SAR developed by Kerdouci et al. (2014), the exocyclic double bond is
expected to be 5 times more reactive than the endocyclic one as it is more
substituted. Nevertheless, all possible pathways were considered here, but
the pathways for only two radicals are presented in Fig. 8 in order to
facilitate the reading (see Fig. S2 for the two others). In most cases, the
products formed are isomers and cannot be distinguished from one path to
another with the techniques used here.
Nitrooxy-alkyl radicals can then react with O2 to form a peroxy radical
(RO2) via reaction 2 in Fig. 8. The formation of an epoxide has also been
observed (152 g mol-1, reaction 3 in Fig. 8), using both NO+ (m/z 152) and
H3O+ (m/z 153) ionization modes. RO2 radicals then react
following different pathways: they can react with NO2 to form a
peroxynitrate, RO2NO2 (MW = 276 g mol-1, where MW denotes molecular weight), following reaction 4 in Fig. 8. This was detected in NO+ ionization mode at m/z 276. This reaction is
usually negligible in the atmosphere but can be significant in simulation
chambers due to high NO2 concentrations. It should also be noted
that peroxynitrates (RO2NO2), which have a characteristic
absorption in the IR region, were not detected in our experiments, neither
in the gaseous phase nor in the aerosol one. This suggests that
RO2+ NO2 reactions are minor pathways. It can also react with
another peroxy radical (RO2+ RO2, reaction 5 in Fig. 8) to form a
characteristic hydroxynitrate (MW = 215 g mol-1) and a ketonitrate
(MW = 213 g mol-1). Both were detected at m/z 216 (M+1) in
H3O+ ionization mode and m/z 214 (M-1) in NO+ mode for the
hydroxynitrate and at m/z 214 (M+1) in H3O+ mode and 243 (M+30) in NO+ mode for the ketonitrate. This reaction involving
an H-atom transfer is possible only if the carbon that carries the peroxy
radical group is linked to a hydrogen, i.e., for primary and secondary peroxy
radicals. Here, this reaction is thus possible only for the peroxy radical
coming from the addition on the endocyclic double bond shown in Fig. 8.
Finally, peroxy radicals can react with another RO2 or with the NO3
radical (reactions 6 and 6′ respectively in Fig. 8) to form an alkoxy radical (RO).
RO radicals can then evolve following reactions 7, 8 and 9 in Fig. 8. They can react
with O2 (reaction 7) to form the same ketonitrate as the one formed by
reaction 5 (MW = 213 g mol-1). In the case of NO3 addition onto the
endocyclic double bond, the resulting alkoxy radical can decompose following
reaction 8, leading to the formation of an alkyl radical, which then reacts
following previously mentioned pathways to form a diketonitrate (MW = 229 g mol-1, framed in green in Fig. 8). This trifunctional product has
been detected in both H3O+ (m/z 230) and NO+ ionization modes
(m/z 229). This alkoxy radical can also decompose by a scission of the
C(ONO2)–CH(O⚫) bond (reaction 9), leading to the formation
of a dicarbonyl ring opening product of MW = 168 g mol-1 (detected at m/z 169 in H3O+ mode and m/z 168 in
NO+ mode). In the case of NO3 addition onto the exocyclic double bond,
the resulting alkoxy can decompose to form a carbonyl product of MW = 110 g mol-1 (detected at m/z 111 in H3O+ mode
and m/z 110 in NO+ mode) and acetone. Acetone has been detected with a
formation yield of 23 %. Considering that this pathway is the only one
allowing the primary production of acetone, a tentative determination of the
branching ratio has been made. As mentioned previously, NO3 addition to
the exocyclic double bond is expected to be the major pathway. The two
resulting alkoxy radicals (see Fig. S3) can both produce acetone by
decomposition but with different expected yields. The radical shown in
Fig. 8, i.e., the one having the radical group on the isopropyl group, is
expected to produce mainly acetone, whereas the other one shown in Fig. S2,
i.e., the one having the radical group on the cycle, is expected to decompose
following the three possible pathways, which have very close activation
energies (Vereecken and Peeters, 2009). Thus, considering the same
probability for the three decomposition pathways, acetone production yield
would be around 30 %. Experimental acetone yield being 23 %, this would
suggest that the alkoxy having the radical group on the cycle is
predominant.
Primary products can themselves react with NO3 because they still
possess a double bond, leading to the formation of second-generation
products, squared in red in Fig. 8. Second-generation products coming from
the carbonyl and the dicarbonyl products have been identified: a
tri-carbonyl compound (MW = 142 g mol-1) and two epoxides
(MW = 184 g mol-1 and MW = 126 g mol-1).
Calculated vapor pressures and their estimated partition in the SOA are
shown next to the products in Fig. 8. Among the first-generation products,
two are likely to participate in SOA formation: the hydroxynitrate and the
diketonitrate. The hydroxynitrate is a product characteristic of the
RO2+ RO2 pathway and has a low vapor pressure because of
the presence of hydrogen bonds. This compound is estimated to be at 40 % in the
SOA phase. However, considering that the addition of NO3 proceeds
mainly by addition onto the exocyclic double bond, the formation of the
hydroxynitrate is expected to be minor. The diketonitrate (MW = 229 g mol-1) is also expected to significantly contribute to SOA formation with a
partition of 90 % in the SOA phase. It can be formed by additions of
NO3 onto both the exocyclic and the endocyclic C=C bonds. For this
trifunctional product, the associate partitioning coefficient,
Kp, has been calculated following Eq. (6).
Considering the uncertainty in ξaeri
due to the vapor pressure estimation, it can vary from 1.1 × 10-2 to 3.4 ×10-3 m3µg-1. This value
is consistent with the partitioning coefficient found with the two-product
model from Eq. (4) (Kp,1=6.7×10-3 m3µg-1), within the associated estimated uncertainty in
Kp.
Identified secondary products have high vapor pressures and thus may not
contribute to the SOA formation. Other products with molecular weights close
to 290 g mol-1 have been detected with weak signals but were not
identified. Due to their high molecular weights, they could significantly
contribute to SOA. In addition, other secondary products may be formed
without being detected by PTR-ToF-MS due to their too low volatility.
β-Caryophyllene oxidation scheme
β-Caryophyllene has two double bonds, one exocylic and one endocyclic,
but according to the Kerdouci et al. (2014) SAR, the exocyclic bond is expected
to be approx. 40 times less reactive than the endocyclic one CH=C < because it is less substituted. So only the addition onto the endocyclic
bond has been considered here, leading to the formation of two possible
nitrooxy-alkyl radicals (see Fig. 9).
Like for terpinolene, alkyl radicals can evolve following two pathways: (i) the formation of an epoxide (MW = 220 g mol-1, reaction 2 in Fig. 9), detected
at m/z 221 in H3O+ ionization mode and m/z 220 in NO+ mode, and
(ii) the formation of a peroxy radical, by reaction with O2 (reaction 3 in Fig. 9). Under high NO2 levels, RO2 radicals can then react with
NO2 to form peroxynitrates (reaction 4 in Fig. 9) of molecular weight MW = 344 g mol-1 (identified at m/z 345 in H3O+ mode and m/z 344 in
NO+ mode). As with terpinolene, these compounds have not been detected
in the gas or particle phase, suggesting that the pathway is minor. RO2
radicals can also undergo self-reactions, leading to the formation of a
characteristic hydroxynitrate and a ketonitrate (reaction 5 in Fig. 9) of molecular
weights MW = 283 and MW = 281 g mol-1 respectively. The hydroxynitrate has
been detected at m/z 284 in H3O+ ionization mode and m/z 282 in
NO+ mode and the ketonitrate at m/z 282 (M+1, H3O+) and m/z 311 (M+30, NO+). As mentioned previously, this reaction is only
possible when the carbon atom which carries the peroxy group is linked to an
H atom so, here, only for one of the two peroxy radicals. Finally, RO2
radicals can react with another peroxy radical or with NO3 (reactions 6
and 6′ in Fig. 9) to form an alkoxy radical. This last one can react with O2 to
form a ketonitrate (MW = 281 g mol-1). The alkoxy radicals can
decompose by a scission of the C(ONO2)–CH(O⚫) bond
associated with a loss of NO2 to form a dicarbonyl product of MW = 236 g mol-1 (m/z 237 in H3O+ mode and m/z 236 in NO+ mode,
reaction 9, framed in orange in Fig. 9). It can also decompose by a C–C breaking on
the other side of the alkoxy group (reaction 8 in Fig. 9) to form a trifunctional
compound (MW = 298 g mol-1), detected at m/z 299 (H3O+) and
m/z 298 (NO+). It should be noted that, in the case where the NO3 radical
adds on to the exocyclic double bond, formaldehyde is expected to be formed
(see Fig. S3), but it was not detected with FTIR (with a detection limit
close to 10 ppb). This information confirms that this pathway is minor.
Even though the reaction of NO3 on the remaining CH2=C <
double bond is expected to be slow, secondary products have been detected
and shown in red in Fig. 9. Second-generation epoxides (MW = 252 g mol-1, m/z 253 in H3O+ mode and m/z 252 in NO+ mode; MW = 222 g mol-1, m/z 223 in H3O+ mode and m/z 222 in NO+
mode) have been measured (reaction 3 in Fig. 9). Also a carbonyl compound of MW = 238 g mol-1 (m/z 239 in H3O+ mode and m/z 238 in NO+
mode) coming from the decomposition of the alkoxy radical (reaction 8-2) has
been detected. A trifunctional species can also be formed by the reaction of
the alkoxy radicals with O2 (reaction 8-2 in Fig. 9). This diketonitrate (MW = 313 g mol-1) was detected in H3O+ mode (m/z 314). Finally, a
nitrogen product which can be a dinitrate has been detected at m/z 327 in
NO+ ionization mode but has not been identified.
As with terpinolene, estimated vapor pressures of detected products and the
corresponding partitioning ratio between the gas and aerosol phase are shown
next to the products in Fig. 9. Because β-caryophyllene is a
sesquiterpene (C15), most of the oxidation products have very low vapor
pressures and can thus contribute to SOA formation. This is in good
agreement with the high SOA yields observed even for low aerosol mass
loading. Only a few products formed by fragmentation processes have relatively
high volatility, thus explaining SOA yields between 50 % and 90 % and not
100 %. Finally, many identified products are also organic nitrates, in
good agreement with gas-phase observations.
The study of Wu
et al. (2021) carried out an identification of SOA composition.
Particle-phase molecular composition was identified using both a Filter Inlet for Gases and AEROsols (FIGAERO) coupled with a chemical ionization mass spectrometer (CIMS) and an extractive electrospray ionization time-of-flight mass spectrometer (EESI-ToF). A large majority of organic nitrates were detected.
C15 monomers are major products, as also shown in our study. C30 dimers have
also been detected, but they are heavy products and out of the PTR-ToF-MS
mass-to-charge ratio range used in our study. In addition, the quantity of
dimers detected in the particle phase can be explained by the reaction of
hydroxynitrates with carbonyl compounds, via an acid-catalyzed
particle-phase reaction leading to the formation of acetal dimers and
trimers, as shown in Claflin and
Ziemann (2018).
This study is in good agreement with the determination of organic nitrates
in the particle phase: a large quantity of organic nitrates was detected, which
confirms their prominence in β-caryophyllene + NO3 SOA
formation. Most of the products were too heavy to be detected in our study,
but two major ones are C15H24O2 (MW = 236 g mol-1) and
C15H25NO5 (MW = 298 g mol-1). They have been identified here as
opening-ring products. This confirms the importance of these two products in
β-caryophyllene + NO3 chemistry.
Discussion and comparison
Yields measured in this study are summarized in Table 5 and compared to
those obtained for other BVOCs by previous studies. It can be observed that
oxidation of terpinolene and β-caryophyllene produces large amounts
of SOA and ONs, similarly to other BVOCs, with two notable exceptions for
α-pinene and α-terpinene. In the case of α-pinene,
larger formation yield of carbonyls was observed in comparison to the others
BVOCs (Ng et al., 2017). These carbonyl compounds being more volatile than
ONs, several previous studies suggest that there is a correlation between
ONs and SOA yields (Hallquist et al., 1999; Fry et al., 2014). Indeed, α-pinene has a low organic nitrate yield, corresponding to almost no SOA
production, when limonene and Δ-carene both exhibit high SOA and
organic nitrate yields. However, the results obtained in a previous
comparative study (Fouqueau et al., 2020b) for α- and γ-terpinene show that α-terpinene does not follow this correlation,
as it produces a large quantity of organic nitrates but almost no SOAs. To
interpret these observations, the mechanisms have to be considered.
Mean SOA and organic nitrate yields obtained in this study for
terpinolene and β-caryophyllene and for other terpenes in the
literature.
As discussed previously in Sect. 4.3 and also in Fouqueau et al. (2020a),
two mechanism steps are critical for SOA formation: the peroxy and the
alkoxy reaction pathways. For the peroxy radicals, this study has shown the
hydroxynitrates coming from the reaction RO2+RO2→ROH+R(O) have low vapor pressures and can contribute to SOA formation. In
the case of terpinolene, this reaction is less favorable than for β-terpinene, for example, because the reaction is estimated to proceed mainly
by addition of NO3 onto the fully substituted exocyclic double bond,
leading to tertiary peroxy radicals. Even though these hydroxynitrates were
detected, their formation yields should be low. For the alkoxy radicals,
several decomposition pathways can occur, forming different types of
products having different volatilities: the scission of the
C(ONO2)–CH(O⚫) bond leads to the formation of volatile
dicarbonyl products. On the contrary, when the alkoxy decomposes by a scission
of the C-C bond located on the other side of the alkoxy group, it produces a
keto-nitrooxy-alkyl radical which then evolves to form a low-vapor
trifunctional species (diketonitrate). The major role of these two steps has
already been pointed out by previous studies. The role of
the RO2+RO2
reaction has been shown to play a significant role in SOA formation from
isoprene (Ng et al., 2008). The role of the alkoxy radical decomposition has
already been raised by Kurten et al. (2017),
suggesting that for Δ-carene, which has a high SOA yield, the
decomposition of alkoxy radicals can lead to the formation of
keto-nitrooxy-alkyl radicals, whereas for α-pinene, the alkoxy
radicals decompose almost exclusively to form the dicarbonyl compound,
explaining the low SOA and ON yields. The mechanisms of terpinolene are thus
in good agreement with these previous studies.
SOA yields obtained for β-caryophyllene are very high, and this can
easily be explained by the size of this precursor (C15). β-Caryophyllene is the only sesquiterpene for which data have been provided,
and comparison of its SOA yield with those obtained for terpenes is not
fully relevant. Nevertheless, the same key steps have been noted in the
mechanism. The addition of NO3 onto the endocyclic double bond is
expected to be the major pathway leading to the formation of the same types
of functionalized products as those observed for terpinolene
(hydroxynitrates, ketonitrates, diketonitrates) but here having much lower
vapor pressures.
Organic nitrate yields of both studied compounds are around 50 %. They
can be compared to those measured for other BVOCs, presented in Table 5:
within the uncertainties, they appear to be similar to those of α-
and γ-terpinene (48 % and 55 % respectively; Fouqueau et al.,
2020a). Limonene has a yield between 30 % and 72 % (Hallquist et al., 1999;
Spittler et al., 2006) and β-pinene between 22 % and 74 % (Boyd et al.,
2015; Fry et al., 2014; Hallquist et al., 1999). They also appear similar to
those of Δ-carene (68 %–77 %; Fry et al., 2014; Hallquist et
al., 1999) and isoprene (62 %–78 %; Rollins et al.,
2009) within the uncertainties. BVOC + NO3 reactions are therefore major
sources of ONs.
Products coming from isomerization were not detected in this study. Even
though this is considered a minor pathway by the calculation of Vereecken and
Peeters (2009), it was proved to be possible in Aschmann et al. (2012) for cycloalkoxy
radicals. Isomerization could thus occur for β-caryophyllene.
Products coming from this pathway were searched for, but none was found.
Nevertheless, this reaction leads to the formation of heavy functionalized
products that can be difficult to measure with a PTR-MS for two reasons: (i) it cannot measure products that are too heavy, which is probably the case for
isomerization products of β-caryophyllene, and (ii) these compounds
can be found largely in the particle phase. No analysis at the molecular scale
was conducted in the particle phase during our experiments. Indeed, in this
study we only measure the total organic nitrates in the aerosol phase from
their IR absorption band. Nitrates formed by this pathway will not be
differenced from other ones. The occurrence of this pathway is thus not in
disagreement with the observation of high SOA formation.
For both compounds, epoxides have been detected. They were not quantified,
but based on previous studies, their formation yields are expected to be
low. Their formation is considered favored only at low oxygen concentration (Berndt and Böge, 1995). Even though their detection has been rare in
previous studies, their formation was already observed in the same
experimental conditions in Fouqueau et al. (2020a). They were also measured
by Skov et al. (1994), who studied the oxidation of some
alkenes and isoprene by NO3. Low epoxide yields have also been
reported by Wangberg et al. (1997) (3 % for α-pinene) and Ng et al. (2008) (>1 % for isoprene).
Conclusions and atmospheric impacts
In summary, this study has provided kinetic and mechanistic data on the
reaction between nitrate radicals and two BVOCs, terpinolene and β-caryophyllene. For the first time, an absolute rate determination was
conducted for β-caryophyllene. Both compounds have been studied using
relative and absolute rate determinations, leading to kinetic data in good
agreement. Due to the presence of two double bonds, they appear to be very
reactive towards nitrate radicals. As far as we know, this is also the first
mechanistic study of the terpinolene + NO3 reaction and the first
determination of ON yields for β-caryophyllene. They both produce
large amounts of ONs in the gas phase, with yields around 50 %. These
compounds have also been detected in the particle phase, with a production yield
of 25 % for the two compounds. In total, these reactions produce around
70 %–80 % of organic nitrates. These compounds were also shown to be good
SOA precursors. At 10 µg m-3, terpinolene has an SOA yield of 5 % when β-caryophyllene has a yield of 40 %. The latter
produces a high amount of SOA, even for low aerosol mass loading. For both
compounds, SOA formation has been explained thanks to the detection of
oxidation products at the molecular scale, which allowed proposing mechanisms.
The SOA yield of terpinolene can be explained by the formation of two types
of low-volatility product: a trifunctional species and a hydroxynitrate.
High SOA yields observed for β-caryophyllene can be explained by the
formation of several high-molecular-weight products. For both compounds,
preferential pathways have been proposed.
In order to evaluate the contribution of the NO3-initiated oxidation to
the total degradation of these BVOCs, atmospheric lifetimes have been
estimated using NO3 concentrations of 10 ppt (typical nighttime
concentration) and 0.1 ppt (low-insolation diurnal concentration;
Khan et al., 2015). It should
be noted that terpinolene is intensively emitted during both the day and the night (Lindwall et al., 2015). These lifetimes are compared to those
estimated for OH and ozone oxidation in Table 6. It can be observed that
terpinolene and β-caryophyllene have very short lifetimes (a few
minutes) towards the NO3 radical in nighttime conditions, confirming that
NO3 oxidation is a major sink for these compounds. During the day, in
low-sunlight conditions, lifetimes are still short (between 2 and 7 h).
They nevertheless are longer than those estimated for OH and ozone
chemistries. NO3 is thus a minor oxidant under these diurnal
conditions. These short lifetimes also demonstrate that oxidation products
will be formed close to the emission area.
Atmospheric lifetimes of terpinolene and β-caryophyllene
with respect to their oxidation by NO3 and OH radicals and by ozone.
* Calculated with [NO3] = 2.5 ×108 molecules cm-3 (10 ppt).** Calculated with [NO3] = 2.5 ×106 molecules cm-3 (0.1 ppt).*** Calculated with [OH] = 2 ×106 molecules cm-3 and
[O3] = 7 ×1011 molecules cm-3.a Calculated with rate constant recommended by IUPAC.b Calculated with rate constant from Corchnoy and
Atkinson (1990).c Calculated with rate constant from Shu and Atkinson (1995).
One characteristic feature of the oxidation of BVOCs by the NO3 radical is
that it produces large amounts of organic nitrates in both gas and aerosol
phases. Even though OH-initiated oxidation can also produce organic nitrates
(through RO2+ NO reactions),
yields are usually lower (Lee et al., 2006).
Another major finding of this study is that the NO3 oxidation of β-caryophyllene and to a lesser extent of terpinolene produces large
amounts of SOA. The yields obtained in this study can be compared to those
measured in previous studies for ozonolysis and OH oxidation. First,
concerning the oxidation by OH radicals, SOA yields measured for terpinolene
were shown to be close to those measured for NO3 oxidation: for low-NOx
conditions, the SOA yield was found to be around 3 % at M0=10µg m-3, but that can reach 40 % for higher aerosol mass
loadings (Friedman and Farmer, 2018; Lee
et al., 2006b). For β-caryophyllene, the SOA yields were shown to
reach 68 % (Lee et al., 2006b). Regarding the ozonolysis, SOA yields have
been found to be 20 % for terpinolene and 45 % for β-caryophyllene (Lee et al., 2006a). Regarding these results, the oxidation
by NO3 produces similar amounts of SOA to the other oxidants.
However, the chemical composition of the aerosol phase is significantly
different.
In conclusion, the most important impacts of this chemistry rely on the
formation of large amounts of organic nitrates (present in both gas and
aerosol phases) and SOA. Organic nitrates play a key role in tropospheric
chemistry because they behave as NOx reservoirs, carrying reactive nitrogen
in remote areas. Their chemistry in gas and aerosol phases is nevertheless
still not well documented. Considering that our study shows large
production of multifunctional organic nitrates, it is necessary to better
understand their reactivity in order to better evaluate their impacts.
Formation of SOA seems, on the other hand, to be strongly dependent on the
structure of the BVOC. Studies at a molecular scale are thus crucial to better
evaluate the impact of this chemistry on SOA formation.
Data availability
SOA yields and the rate constant for the NO3 oxidation of terpinolene and
β-caryophyllene are available in Table 2. They are also available through
the Library of Advanced Data Products (LADP) of the EUROCHAMP Data Centre
(https://data.eurochamp.org/data-access/photolysis-frequencies-quantum-yields/, Fouqueau et al., 2021a). The simulation chamber
experiments' raw data, which have served as a basis for both the kinetic and the
mechanistic work are available through the Database of Atmospheric
Simulation Chamber Studies (DASCS) of the EUROCHAMP Data Centre
(https://data.eurochamp.org/data-access/chamber-experiments/, Fouqueau et al., 2021b).
The supplement related to this article is available online at: https://doi.org/10.5194/acp-22-6411-2022-supplement.
Author contributions
BPV and MCi coordinated the research project. AF, BPV, MCi and JFD designed
the experiments in the simulation chambers. AF performed the experiments
with the technical support of MCa and EP and performed the data treatment and
interpretation with MCi and BPV. AF, BPV and MCi wrote the paper, and AF was
responsible for the final version of the paper. All co-authors revised the
content of the original manuscript and approved the final version of the
paper.
Competing interests
The contact author has declared that neither they nor their co-authors have any competing interests.
Disclaimer
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Acknowledgements
The authors thank Marie-Thérèse and Jean-Claude Rayez (ISM,
Bordeaux, France) for helping in understanding the reactivity with theoretical
calculation and thank Marie Camredon (LISA, Créteil, France) for helping with
the GECKO-A website. The authors also gratefully acknowledge CNRS INSU for
supporting the CESAM national facility as a component of the ACTRIS French
research infrastructure. The AERIS data center (https://www.aeris-data.fr/, last access: 1 May 2021) is
also gratefully acknowledged for curating and distributing the data as the
data center of the EUROCHAMP-2020 Integrated Activities.
Financial support
This work was supported by the French national program LEFE INSU (CNRS)
and by the Horizon 2020 research and innovation program through the
EUROCHAMP-2020 Infrastructure Activity (grant no. 730997).
This work was also supported by grants from Région Île-de-France.
Review statement
This paper was edited by Harald Saathoff and reviewed by two anonymous referees.
ReferencesAoki, N., Inomata, S., and Tanimoto, H.: Detection of C1-C5 alkyl nitrates
by proton transfer reaction time-of-flight mass spectrometry, Int. J. Mass. Spectrom., 263, 12–21,
2007.Aschmann, S. M., Arey, J., and Atkinson, R.: Kinetics and Products of the
Reactions of OH Radicals with Cyclohexene, 1-Methyl-1-cyclohexene,
cis-Cyclooctene, and cis-Cyclodecene, J. Phys. Chem. A., 116, 9507–15, 10.1021/jp307217m, 2012.Atkinson, R.: Kinetics and mechanisms of the gas-phase reactions of the
hydroxyl radical with organic compounds under atmospheric conditions, Chem. Rev., 86,
69–201, 1986.Atkinson, R., Plum, C. N., Carter, W. P. L., Winer, A. M., and Pitts, J. N.:
Rate constants for the gas-phase reactions of nitrate radicals with a series
of organics in air at 298 .+-. 1 K, J. Phys. Chem., 88, 1210–1215,
10.1021/j150650a039, 1984a.Atkinson, R., Aschmann, S. M., Winer, A. M., and Pitts, J. N.: Kinetics
of the gas-phase reactions of nitrate radicals with a series of dialkenes,
cycloalkenes, and monoterpenes at 295 .+-. 1 K, Environ. Sci. Technol.,
18, 370–375, 10.1021/es00123a016, 1984b.Atkinson, R., Aschmann, S. M., and Pitts, J. N.: Rate constants for the
gas-phase reactions of the nitrate radical with a series of organic
compounds at 296 .+-. 2 K, 92, 3454–3457,
10.1021/j100323a028, 1988.Benter, T., Becker, E., Wille, U., Rahman, M. M., and Schindler, R. N.: The
Determination of Rate Constants for the Reactions of Some Alkenes with the
NO3 Radical, Berichte der Bunsengesellschaft für physikalische Chemie,
96, 769–775, 10.1002/bbpc.19920960607, 1992.Berndt, T. and Böge, O.: Products and Mechanism of the Reaction of NO3
with Selected Acyclic Monoalkenes, J. Atmos. Chem., 21, 275–291, 1995.Berndt, T., Kind, I., and Karbach, H.-J.: Kinetics of the Gas-Phase Reaction
of NO3 Radicals with 1-Butene, trans-Butene, 2-Methyl-2-butene and
2,3-Dimethyl-2-butene Using LIF Detection, Berichte der Bunsengesellschaft
für physikalische Chemie, 102, 1486–1491,
10.1002/bbpc.199800017, 1998.Boyd, C. M., Sanchez, J., Xu, L., Eugene, A. J., Nah, T., Tuet, W. Y., Guzman, M. I., and Ng, N. L.: Secondary organic aerosol formation from the β-pinene+NO3 system: effect of humidity and peroxy radical fate, Atmos. Chem. Phys., 15, 7497–7522, 10.5194/acp-15-7497-2015, 2015.Brown, S. S. and Stutz, J.: Nighttime radical observations and chemistry,
Chem. Soc. Rev., 41, 6405–6447, 10.1039/C2CS35181A, 2012.Calvert, J. G., Orlando, J. J., Stockwell, W. R., and Wallington, T. J.: The
Mechanisms of Reactions Influencing Atmospheric Ozone, Oxford University
Press, New York, ISBN: 9780190233020, 2015.Claflin, M. S. and Ziemann, P. J.: Identification and Quantitation of
Aerosol Products of the Reaction of β-Pinene with NO3 Radicals and
Implications for Gas- and Particle-Phase Reaction Mechanisms, J. Phys. Chem.
A, 122, 3640–3652, 10.1021/acs.jpca.8b00692, 2018.Corchnoy, S. B. and Atkinson, R.: Kinetics of the gas-phase reactions of
hydroxyl and nitrogen oxide (NO3) radicals with 2-carene, 1,8-cineole,
p-cymene, and terpinolene, Environ. Sci. Technol., 24, 1497–1502, 1990.Doussin, J.-F., Durand-Jolibois, R., Ritz, D., Monod, A., and Carlier, P.:
Design of an environmental chamber for the study of atmospheric chemistry:
New developments in the analytical device, 25, 236 p., 1997.Draper, D. C., Farmer, D. K., Desyaterik, Y., and Fry, J. L.: A qualitative comparison of secondary organic aerosol yields and composition from ozonolysis of monoterpenes at varying concentrations of NO2, Atmos. Chem. Phys., 15, 12267–12281, 10.5194/acp-15-12267-2015, 2015.Duncianu, M., David, M., Kartigueyane, S., Cirtog, M., Doussin, J.-F., and Picquet-Varrault, B.: Measurement of alkyl and multifunctional organic nitrates by proton-transfer-reaction mass spectrometry, Atmos. Meas. Tech., 10, 1445–1463, 10.5194/amt-10-1445-2017, 2017.Fouqueau, A., Cirtog, M., Cazaunau, M., Pangui, E., Doussin, J.-F., and Picquet-Varrault, B.: A comparative and experimental study of the reactivity with nitrate radical of two terpenes: α-terpinene and γ-terpinene, Atmos. Chem. Phys., 20, 15167–15189, 10.5194/acp-20-15167-2020, 2020a.Fouqueau, A., Cirtog, M., Cazaunau, M., Pangui, E., Zapf, P., Siour, G., Landsheere, X., Méjean, G., Romanini, D., and Picquet-Varrault, B.: Implementation of an incoherent broadband cavity-enhanced absorption spectroscopy technique in an atmospheric simulation chamber for in situ NO3 monitoring: characterization and validation for kinetic studies, Atmos. Meas. Tech., 13, 6311–6323, 10.5194/amt-13-6311-2020, 2020b.Fouqueau, A., Cirtog, M., Cazaunau, M., Pangui, E., Doussin, J.-F., and Picquet-Varrault, B.: Library of Advanced Data Products: Photolysis Frequencies & Quantum yields [data set], https://data.eurochamp.org/data-access/photolysis-frequencies-quantum-yields/ (last access: 1 May 2021), 2021a.Fouqueau, A., Cirtog, M., Cazaunau, M., Pangui, E., Doussin, J.-F., and Picquet-Varrault, B.: Database of Atmospheric Simulation Chamber Studies [data set], https://data.eurochamp.org/data-access/chamber-experiments/ (last access: 1 May 2021), 2021b.Friedman, B. and Farmer, D. K.: SOA and gas phase organic acid yields from
the sequential photooxidation ofseven monoterpenes, Atmos. Environ., 187, 335–345, 2018.Fry, J. L., Draper, D. C., Barsanti, K. C., Smith, J. N., Ortega, J.,
Winkler, P. M., Lawler, M. J., Brown, S. S., Edwards, P. M., Cohen, R. C.,
and Lee, L.: Secondary Organic Aerosol Formation and Organic Nitrate Yield
from NO3 Oxidation of Biogenic Hydrocarbons, Environ. Sci. Technol., 48,
11944–11953, 10.1021/es502204x, 2014.Geron, C., Rasmussen, R., R. Arnts, R., and Guenther, A.: A review and
synthesis of monoterpene speciation from forests in the United States,
Atmos. Environ., 34, 1761–1781,
10.1016/S1352-2310(99)00364-7, 2000.Gómez-González, Y., Surratt, J. D., Cuyckens, F., Szmigielski, R.,
Vermeylen, R., Jaoui, M., Lewandowski, M., Offenberg, J. H., Kleindienst, T.
E., Edney, E. O., Blockhuys, F., Alsenoy, C. V., Maenhaut, W., and Claeys,
M.: Characterization of organosulfates from the photooxidation of isoprene
and unsaturated fatty acids in ambient aerosol using liquid
chromatography/(-) electrospray ionization mass spectrometry, J. Mass. Spectrom., 43, 371–382,
2008.Gordon, I. E., Rothman, L. S., Hill, C., Kochanov, R. V., Tan, Y., Bernath,
P. F., Birk, M., Boudon, V., Campargue, A., Chance, K. V., Drouin, B. J.,
Flaud, J.-M., Gamache, R. R., Hodges, J. T., Jacquemart, D., Perevalov, V.
I., Perrin, A., Shine, K. P., Smith, M.-A. H., Tennyson, J., Toon, G. C.,
Tran, H., Tyuterev, V. G., Barbe, A., Császár, A. G., Devi, V. M.,
Furtenbacher, T., Harrison, J. J., Hartmann, J.-M., Jolly, A., Johnson, T.
J., Karman, T., Kleiner, I., Kyuberis, A. A., Loos, J., Lyulin, O. M.,
Massie, S. T., Mikhailenko, S. N., Moazzen-Ahmadi, N., Müller, H. S. P.,
Naumenko, O. V., Nikitin, A. V., Polyansky, O. L., Rey, M., Rotger, M.,
Sharpe, S. W., Sung, K., Starikova, E., Tashkun, S. A., Auwera, J. V.,
Wagner, G., Wilzewski, J., Wcisło, P., Yu, S., and Zak, E.
J.: The HITRAN2016 molecular spectroscopic database, J. Quant.
Spectrosc. Ra., 203, 3–69,
10.1016/j.jqsrt.2017.06.038, 2017.Guenther, A., Hewitt, C. N., Erickson, D., Fall, R., Geron, C., Graedel, T.,
Harley, P., Klinger, L., Lerdau, M., Mckay, W. A., Pierce, T., Scholes, B.,
Steinbrecher, R., Tallamraju, R., Taylor, J., and Zimmerman, P.: A global
model of natural volatile organic compound emissions, J. Geophys. Res.-Atmos., 100, 8873–8892, 1995.Guenther, A. B., Jiang, X., Heald, C. L., Sakulyanontvittaya, T., Duhl, T., Emmons, L. K., and Wang, X.: The Model of Emissions of Gases and Aerosols from Nature version 2.1 (MEGAN2.1): an extended and updated framework for modeling biogenic emissions, Geosci. Model Dev., 5, 1471–1492, 10.5194/gmd-5-1471-2012, 2012.Hallquist, M., Wangberg, I., Ljungstrom, E., Barnes, I., and Becker, E.:
Aerosol and Product Yields from NO3 Radical-Initiated Oxidation of Selected
Monoterpenes, Environ. Sci. Technol., 33, 553–559, 1999.Hao, L. Q., Kortelainen, A., Romakkaniemi, S., Portin, H., Jaatinen, A., Leskinen, A., Komppula, M., Miettinen, P., Sueper, D., Pajunoja, A., Smith, J. N., Lehtinen, K. E. J., Worsnop, D. R., Laaksonen, A., and Virtanen, A.: Atmospheric submicron aerosol composition and particulate organic nitrate formation in a boreal forestland–urban mixed region, Atmos. Chem. Phys., 14, 13483–13495, 10.5194/acp-14-13483-2014, 2014.Hjorth, J., Ottobrini, G., Cappellani, F., and Restelli, G.: A Fourier
transform infrared study of the rate constant of the homogeneous gas-phase
reaction nitrogen oxide (N2O5)+ water and determination of absolute
infrared band intensities of N2O5 and nitric acid, J. Phys. Chem., 91,
1565–1568, 10.1021/j100290a055, 1987.Iinuma, Y., Müller, C., Berndt, T., Böge, O., Claeys, M., and
Herrmann, H.: Evidence for the Existence of Organosulfates from β-Pinene
Ozonolysis in Ambient Secondary Organic Aerosol, Environ. Sci. Technol., 41,
6678–6683, 10.1021/es070938t, 2007.Ito, A., Sillman, S., and Penner, J. E.: Effects of additional nonmethane
volatile organic compounds, organic nitrates, and direct emissions of
oxygenated organic species on global tropospheric chemistry, J. Geophys. Res.-Atmos., 112, D06309,
10.1029/2005JD006556, 2007.Jaoui, M., Kleindienst, T. E., Docherty, K. S., Lewandowski, M., and
Offenberg, J. H.: Secondary organic aerosol formation from the oxidation of
a series of sesquiterpenes: α-cedrene, β-caryophyllene,
α-humulene and α-farnesene with O3, OH and NO3 radicals, Environ. Chem., 10, 178–193,
2013.Kerdouci, J., Picquet-Varrault, B., and Doussin, J. F.: Structure–activity
relationship for the gas-phase reactions of NO3 radical with organic
compounds: Update and extension to aldehydes, Atmos. Environ., 84, 363–372,
10.1016/j.atmosenv.2013.11.024, 2014.Khan, M. A. H., Morris, W. C., Watson, L. A., Galloway, M., Hamer, P. D.,
Shallcross, B. M. A., Percival, C. J., and Shallcross, D. E.: Estimation of
Daytime NO3 Radical Levels in the UK Urban Atmosphere Using the Steady State
Approximation Method, Adv. Meteorol., 2015, e294069, 10.1155/2015/294069,
2015.Kiendler-Scharr, A., Mensah, A., Friese, E., Topping, D., Nemitz, E.,
Prevot, A. S. H., Äijälä, M., Allan, J., Canonaco, F.,
Canagaratna, M., Carbone, S., Crippa, M., Dall'Osto, M., Day, D. A., De
Carlo, P., Di Marco, C. F., Elbern, H., Eriksson, A., Freney, E., Hao, L.,
Herrmann, H., Hildebrandt, L., Hillamo, R., Jimenez, J. L., Laaksonen, A.,
McFiggans, G., Mohr, C., O'Dowd, C., Otjes, R., Ovadnevaite, J., Pandis, S.
N., Poulain, L., Schlag, P., Sellegri, K., Swietlicki, E., Tiitta, P.,
Vermeulen, A., Wahner, A., Wornsnop, D., and Wu, H.-C.: Ubiquity of organic
nitrates from nighttime chemistry in the European submicron aerosol, Geophys. Res. Lett., 43,
7735–7744, 10.1002/2016GL069239, 2016.Kurten, T., Moller, K. H., Nguyen, T. B., Schwantes, R. H., Misztal, P. K.,
Su, L., Wennberg, P. O., Fry, J. L., and Kjaergaard, H. G.: Alkoxy Radical
Bond Scissions Explain the Anomalously Low Secondary Organic Aerosol and
Organonitrate Yields From α-Pinene + NO3, J. Phys. Chem. Lett., 8, 2826–2834,
10.1021/acs.jpclett.7b01038, 2017.Lai, A. C. K. and Nazaroff, W. W.: Modeling indoor particle deposition from
turbulent flow onto smooth surfaces, J. Aerosol Sci., 31, 463–476,
10.1016/S0021-8502(99)00536-4, 2000.Lamkaddam, H., Gratien, A., Pangui, E., Cazaunau, M., Picquet-Varrault, B.,
and Doussin, J.-F.: High-NOx Photooxidation of n-Dodecane: Temperature
Dependence of SOA Formation, Environ. Sci. Technol., 51, 192–201,
10.1021/acs.est.6b03821, 2017.Lancar, I. T., Daele, V., Lebras, G., and Poulet, G.: Reaction of NO3
radicals with 2,3-dimethylbut-2-ene, buta-1,3-diene and
2,3-dimethylbuta-1,3-diene, J. Chim. Phys. Pcb., 88, 1777–1792,
1991.Lee, A., Goldstein, A. H., Kroll, J. H., Ng, N. L., Varutbangkul, V.,
Flagan, R. C., and Seinfeld, J. H.: Gas-phase products and secondary aerosol
yields from the photooxidation of 16 different terpenes, 111, D17305, 10.1029/2006JD007050, 2006.Lee, B. H., Mohr, C., Lopez-Hilfiker, F. D., Lutz, A., Hallquist, M., Lee,
L., Romer, P., Cohen, R. C., Iyer, S., Kurten, T., Hu, W., Day, D. A.,
Campuzano-Jost, P., Jimenez, J. L., Xu, L., Ng, N. L., Guo, H., Weber, R.
J., Wild, R. J., Brown, S. S., Koss, A., de Gouw, J. A., Olson, K.,
Goldstein, A. H., Seco, R., Kim, S., McAvey, K., Shepson, P. B., Starn, T.,
Baumann, K., Edgerton, E. S., Liu, J., Shilling, J. E., Miller, D. O.,
Brune, W., Schobesberger, S., D'Ambro, E. L., and Thornton, J. A.: Highly
functionalized organic nitrates in the southeast United States: Contribution
to secondary organic aerosol and reactive nitrogen budgets, P. Natl. Acad. Sci. USA, 113, 1516–1521,
10.1073/pnas.1508108113, 2016.Lindwall, F., Faubert, P., and Rinnan, R.: Diel Variation of Biogenic
Volatile Organic Compound Emissions–A field Study in the Sub, Low and High
Arctic on the Effect of Temperature and Light, PLoS ONE, 10, e0123610, 10.1371/journal.pone.0123610, 2015.Martinez, E., Cabanas, B., Aranda, A., Martin, P., Notario, A., and Salgado,
S.: Study on the NO3 Radical Reactivity: Reactions with Cyclic Alkenes,
J. Phys. Chem. A, 103, 5321–5327, 1999.McGillen, M. R., Carter, W. P. L., Mellouki, A., Orlando, J. J., Picquet-Varrault, B., and Wallington, T. J.: Database for the kinetics of the gas-phase atmospheric reactions of organic compounds, Earth Syst. Sci. Data, 12, 1203–1216, 10.5194/essd-12-1203-2020, 2020.Müller, M., Graus, M., Wisthaler, A., Hansel, A., Metzger, A., Dommen, J., and Baltensperger, U.: Analysis of high mass resolution PTR-TOF mass spectra from 1,3,5-trimethylbenzene (TMB) environmental chamber experiments, Atmos. Chem. Phys., 12, 829–843, 10.5194/acp-12-829-2012, 2012.Newland, M. J., Ren, Y., McGillen, M. R., Michelat, L., Daële, V., and Mellouki, A.: NO3 chemistry of wildfire emissions: a kinetic study of the gas-phase reactions of furans with the NO3 radical, Atmos. Chem. Phys., 22, 1761–1772, 10.5194/acp-22-1761-2022, 2022.Ng, N. L., Kwan, A. J., Suratt, J. D., Chan, A. W. H., Chhabra, P. S.,
Sorooshian, A., Pye, H. O. T., Crounse, J. D., Wennberg, P. O., Flagan, R.
C., and Seinfeld, J. H.: Secondary organic aerosol (SOA) formation from
reaction of isoprene with nitrate radicals (NO3), 8, 4117–4140, 2008.Ng, N. L., Brown, S. S., Archibald, A. T., Atlas, E., Cohen, R. C., Crowley, J. N., Day, D. A., Donahue, N. M., Fry, J. L., Fuchs, H., Griffin, R. J., Guzman, M. I., Herrmann, H., Hodzic, A., Iinuma, Y., Jimenez, J. L., Kiendler-Scharr, A., Lee, B. H., Luecken, D. J., Mao, J., McLaren, R., Mutzel, A., Osthoff, H. D., Ouyang, B., Picquet-Varrault, B., Platt, U., Pye, H. O. T., Rudich, Y., Schwantes, R. H., Shiraiwa, M., Stutz, J., Thornton, J. A., Tilgner, A., Williams, B. J., and Zaveri, R. A.: Nitrate radicals and biogenic volatile organic compounds: oxidation, mechanisms, and organic aerosol, Atmos. Chem. Phys., 17, 2103–2162, 10.5194/acp-17-2103-2017, 2017.Odum, J. R., Hoffmann, T., Bowman, F., Collins, D., Flagan, R. C., and
Seinfeld, J. H.: Gas/Particle Partitioning and Secondary Organic Aerosol
Yields, Environ. Sci. Technol., 30, 2580–2585, 1996.Orphal, J., Fellows, C. E., and Flaud, P.-M.: The visible absorption
spectrum of NO3 measured by high-resolution Fourier transform
spectroscopy, 108, 4077, 10.1029/2002JD002489, 2003.Pankow, J. F. and Asher, W. E.: SIMPOL.1: a simple group contribution method for predicting vapor pressures and enthalpies of vaporization of multifunctional organic compounds, Atmos. Chem. Phys., 8, 2773–2796, 10.5194/acp-8-2773-2008, 2008.Picquet-Varrault, B., Scarfogliero, M., Ait Helal, W., and Doussin,
J.-F.: Reevaluation of the rate constant for the reaction propene +NO3 by absolute rate determination, International Journal of Chemical
Kinetics, 41, 73–81, 2009.Picquet-Varrault, B., Suarez-Bertoa, R., Duncianu, M., Cazaunau, M., Pangui, E., David, M., and Doussin, J.-F.: Photolysis and oxidation by OH radicals of two carbonyl nitrates: 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone, Atmos. Chem. Phys., 20, 487–498, 10.5194/acp-20-487-2020, 2020.Rahman, M. M., Becker, E., Benter, Th., and Schindler, R. N.: A Gasphase
Kinetic Investigation of the System F +HNO3 and the Determination of
Absolute Rate Constants for the Reaction of the NO3 Radical with CH3SH,
2-Methylpropene, 1,3-Butadiene and 2,3-Dimethyl-2-Butene, Berichte der
Bunsengesellschaft für physikalische Chemie, 92, 91–100,
10.1002/bbpc.198800018, 1988.Rindelaub, J. D., McAvey, K. M., and Shepson, P. B.: The photochemical
production of organic nitrates from a-pinene and loss via acid-dependent
particle phase hydrolysis, Atmos. Environ., 100, 193–201, 2015.Rollins, A. W., Kiendler-Scharr, A., Fry, J. L., Brauers, T., Brown, S. S., Dorn, H.-P., Dubé, W. P., Fuchs, H., Mensah, A., Mentel, T. F., Rohrer, F., Tillmann, R., Wegener, R., Wooldridge, P. J., and Cohen, R. C.: Isoprene oxidation by nitrate radical: alkyl nitrate and secondary organic aerosol yields, Atmos. Chem. Phys., 9, 6685–6703, 10.5194/acp-9-6685-2009, 2009.Rothman, L. S., Barbe, A., Chris Benner, D., Brown, L. R., Camy-Peyret, C.,
Carleer, M. R., Chance, K., Clerbaux, C., Dana, V., Devi, V. M., Fayt, A.,
Flaud, J.-M., Gamache, R. R., Goldman, A., Jacquemart, D., Jucks, K. W.,
Lafferty, W. J., Mandin, J.-Y., Massie, S. T., Nemtchinov, V., Newnham, D.
A., Perrin, A., Rinsland, C. P., Schroeder, J., Smith, K. M., Smith, M. A.
H., Tang, K., Toth, R. A., Vander Auwera, J., Varanasi, P., and Yoshino, K.:
The HITRAN molecular spectroscopic database: edition of 2000 including
updates through 2001, J. Quant. Spectrosc. Ra., 82, 5–44, 10.1016/S0022-4073(03)00146-8, 2003.Schott, G. and Davidson, N.: Shock waves in chemical kinetics: The
decomposition of N2O5 at high temperatures, 80, 1841–1853, 1958.Shu, Y. and Atkinson, R.: Atmospheric lifetimes and fates of a series of
sesquiterpenes, 100, 7275–7281, 1995.Skov, H., Benter, T., Schindler, R. N., Hjorth, J., and Restelli, G.:
Epoxide formation in the reactions of the nitrate radical with
2,3-dimethyl-2-butene, cis- and trans-2-butene and isoprene, Atmos. Environ., 28, 1583–1592,
1994.Slade, J. H., de Perre, C., Lee, L., and Shepson, P. B.: Nitrate radical oxidation of γ-terpinene: hydroxy nitrate, total organic nitrate, and secondary organic aerosol yields, Atmos. Chem. Phys., 17, 8635–8650, 10.5194/acp-17-8635-2017, 2017.Spittler, M., Barnes, I., Bejan, I., Brockmann, K. J., Benter, Th., and
Wirtz, K.: Reactions of NO3 radicals with limonene and α-pinene: Product
and SOA formation, Atmos. Environ., 40, 116–127,
10.1016/j.atmosenv.2005.09.093, 2006.Stewart, D. J., Almabrok, S. H., Lockhart, J. P., Mohamed, O. M., Nutt, D.
R., Pfrang, C., and Marston, G.: The kinetics of the gas-phase reactions of
selected monoterpenes and cyclo-alkenes with ozone and the NO3 radical,
Atmos. Environ., 70, 227–235,
10.1016/j.atmosenv.2013.01.036, 2013.Suarez-Bertoa, R., Picquet-Varrault, B., Tamas, W., Pangui, E., and Doussin,
J.-F.: Atmospheric Fate of a Series of Carbonyl Nitrates: Photolysis
Frequencies and OH-Oxidation Rate Constants, Environ. Sci. Technol., 46, 12502–12509, 2012.Valorso, R., Aumont, B., Camredon, M., Raventos-Duran, T., Mouchel-Vallon, C., Ng, N. L., Seinfeld, J. H., Lee-Taylor, J., and Madronich, S.: Explicit modelling of SOA formation from α-pinene photooxidation: sensitivity to vapour pressure estimation, Atmos. Chem. Phys., 11, 6895–6910, 10.5194/acp-11-6895-2011, 2011.Vandaele, A. C., Hermans, C., Simon, P. C., Carleer, M., Colin, R., Fally,
S., Mérienne, M. F., Jenouvrier, A., and Coquart, B.: Measurements of
the NO2 absorption cross-section from 42 000 cm-1 to 10 000 cm-1 (238–1000 nm)
at 220 K and 294 K, J. Quant. Spectrosc. Ra., 59, 171–184, 1997.Vereecken, L. and Peeters, J.: Decomposition of substituted alkoxy
radicals – part I: a generalized structure–activity relationship for
reaction barrier heightsw, Phys. Chem. Chem. Phys., 11, 9062–9074, 10.1039/b909712k,
2009.Wangberg, I., Barnes, I., and Becker, K. H.: Product and mechanistic study
of the reaction of NO3 radicals with alpha-pinene, Environ. Sci. Technol.,
31, 2130–2135, 1997.Wang, J., Doussin, J.-F., Perrier, S., Perraudin, E., Katrib, Y., Pangui,
E., and Picquet-Varrault, B.: Design of a new multi-phase experimental
simulation chamber for atmospheric photosmog, Aerosol and Cloud Chemistry
Research, 4, 2465–2494, 2011.Wu, C., Bell, D. M., Graham, E. L., Haslett, S., Riipinen, I., Baltensperger, U., Bertrand, A., Giannoukos, S., Schoonbaert, J., El Haddad, I., Prevot, A. S. H., Huang, W., and Mohr, C.: Photolytically induced changes in composition and volatility of biogenic secondary organic aerosol from nitrate radical oxidation during night-to-day transition, Atmos. Chem. Phys., 21, 14907–14925, 10.5194/acp-21-14907-2021, 2021.
Xu, L., Suresh, S., Guo, H., Weber, R. J., and Ng, N. L.: Aerosol characterization over the southeastern United States using high-resolution aerosol mass spectrometry: spatial and seasonal variation of aerosol composition and sources with a focus on organic nitrates, Atmos. Chem. Phys., 15, 7307–7336, 10.5194/acp-15-7307-2015, 2015.