Heterogeneous reactivity of N2O5 on aerosols is
a critical parameter in assessing NOx fate, nitrate production, and
particulate chloride activation. Accurate measurement of its uptake
coefficient (γN2O5) and representation in air quality models
are challenging, especially in the polluted environment. With an in situ
aerosol flow-tube system, the γN2O5 was directly measured on
ambient aerosols at two rural sites in northern and southern China. The
results were analyzed together with the γN2O5 derived from
previous field studies in China to obtain a holistic picture of
N2O5 uptake and the influencing factors under various climatic and
chemical conditions. The field-derived or measured γN2O5 was
generally promoted by the aerosol water content and suppressed by particle
nitrate. Significant discrepancies were found between the measured γN2O5 and that estimated from laboratory-determined parameterizations.
An observation-based empirical parameterization was derived in the present
work, which better reproduced the mean value and variability of the observed
γN2O5. Incorporating this new parameterization into a regional
air quality model (WRF-CMAQ) has improved the simulation of N2O5,
nitrogen oxides, and secondary nitrate in the polluted regions of China.
Introduction
Heterogeneous reaction of dinitrogen pentoxide (N2O5) on aerosol
surfaces plays an important role in the nocturnal removal of nitrogen oxides
(NOx), secondary nitrate formation, and chlorine activation through nitryl chloride (ClNO2) production on chloride-containing aerosols (Brown et al., 2006; Osthoff et al., 2008; Thornton et al., 2010; Wang et al., 2016). Realistically representing this process in air quality models is therefore necessary for the prediction and mitigation of ground-level ozone
and particulate pollution. The currently accepted mechanism of the
heterogeneous reaction of N2O5 on aqueous aerosols starts with the
mass accommodation of N2O5 on aerosol surface (Reaction R1), followed by reversible N2O5 hydrolysis to form nitrate and intermediate
H2ONO2+ in the aqueous phase (Reaction R2). The intermediate
H2ONO2+ will react with H2O or Cl- to form
HNO3 or ClNO2, respectively (Reactions R3 and R4) (Behnke et al., 1997; Finlayson-Pitts et al., 1989; Schweitzer et al., 1998; Thornton and Abbatt, 2005; Bertram and Thornton, 2009).
R1N2O5(g)⟶k1N2O5(aq),R2N2O5(aq)+H2O(l)⇄k2fk2bH2ONO2+(aq)+NO3-(aq),R3H2ONO2+(aq)+H2O(l)⟶k3H3O+(aq)+HNO3(aq),R4H2ONO2+(aq)+Cl-(aq)⟶k4ClNO2(g)+H2O(l).
The reaction probability of N2O5, the so-called uptake coefficient
γN2O5, is the fraction of N2O5 net removal upon
collisions on aerosols, and it is a key parameter to describe the heterogeneous
loss rate of N2O5 on ambient aerosols. γN2O5 was
first measured using aerosol flow tubes in the laboratory, and it was shown
to be dependent on aerosol chemical compositions such as water content, nitrate
concentration, chloride concentration, and organic coatings. Specifically,
the aerosol water content can enhance the N2O5 uptake by promoting
the hydrolysis of N2O5 (e.g., Hallquist et al., 2003; Thornton et
al., 2003), while nitrate favors the reverse of Reaction (R2) and thus
suppress the N2O5 uptake (e.g., Wahner et al., 1998; Bertram and
Thornton, 2009). On the contrary, chloride in the aqueous aerosol will react
with the intermediate H2ONO2+ faster than NO3- and
negate the nitrate suppression effect (e.g., Behnke et al., 1997;
Bertram and Thornton, 2009). Organic coatings also can suppress
N2O5 uptake by inhibiting the mass accommodation of N2O5
or limiting the availability of liquid water on the aerosol surface (e.g., Thornton and Abbatt, 2005; Anttila et al., 2006; Cosman et al.,
2008; Gaston et al., 2014). Based on the laboratory studies, several
parameterizations have been proposed to predict the variations of γN2O5, with considerations of temperature, relative humidity (RH), aerosol water content, nitrate, chloride, aerosol volume to surface area ratio, and organic coatings (Davis et al., 2008; Evans and Jacob, 2005; Anttila et al., 2006; Riemer et al., 2009; Griffiths et al., 2009; Bertram and Thornton, 2009).
To investigate the heterogeneous process of N2O5 in ambient
environments, γN2O5 was also derived from ambient
concentrations of N2O5 with several methods, including
steady-state lifetime estimation (Brown et al., 2006, 2009, 2016), secondary products formation rate determination
(Phillips et al., 2016), and inverse iterative box model calculation (Wagner
et al., 2013). In addition, aerosol flow tubes have been deployed to the
field solely or in combination with an iterative model to directly “measure”
γN2O5 on ambient aerosols (Bertram et al., 2009a; Wang
et al., 2018). Several studies have compared the field-derived or measured
γN2O5 with that calculated from the parameterizations based on
the laboratory results, which revealed significant discrepancies between
them and large variations in the relationship between γN2O5 and aerosol chemical composition (e.g., Riedel et
al., 2012; Morgan et al., 2015; Z. Wang et al., 2017; Tham et al., 2018;
McDuffie et al., 2018a). Recently, McDuffie et al. (2018a) proposed an
empirical parameterization based on the aircraft measurements of
N2O5 in the eastern United States, which can reproduce the mean
value of the field-derived γN2O5 but still has difficulty in
explaining its large variability. The discrepancies between the
field-derived or measured and parameterized γN2O5 lie in the
differences between the complex aerosols in ambient conditions and the
simple proxies used in laboratory studies, e.g., more complex organic
matter or mixing state of ambient aerosols, and these discrepancies highlight the demand for
the further comprehensive investigation of N2O5 uptake in diverse
atmospheric conditions.
To further investigate the active N2O5 heterogeneous process
revealed in previous studies in China (e.g., Z. Wang et al., 2017; H. Wang et al., 2017; Tham et al., 2018; Yun et al., 2018), direct measurements of
γN2O5 were conducted at two rural sites in northern and
southern China in this work, by using the recently improved aerosol
flow-tube system (Wang et al., 2018). Integrating them with the previous
field results in various regions of China, we examine in detail the key
factors that determine the γN2O5 and compare them with
laboratory-derived parameterizations. Then we propose improved parameters
for γN2O5 to better represent the N2O5 reactivity in
polluted regions of China, and model simulations with incorporation of the
new parameters were also performed to evaluate the representativeness and
applicability of the new parameterization.
Method
Field measurements of γN2O5 and related parameters were
conducted at a semirural site (Heshan) in southern China from 22 February
to 28 March 2017 and at a mountain site (Mt. Tai) in northern China from 11 March to 8 April 2018. The Heshan site is located on a small hill
(22.73∘ N, 112.92∘ E; 60 m a.s.l.), surrounded by
subtropical trees and some farmland. A small city, Heshan, is 10 km to the
northeast of the site, and three large cities, Guangzhou (the capital of
Guangdong Province), Foshan, and Jiangmen, are 80 km to the northeast, 50 km
to the northeast, and 30 km to the southwest of the site, respectively. The
site is affected by vehicle emissions from three highways and two provincial
roads within 10 km and some residential and agricultural activities in the area,
and it was considered a semirural site. The Mt. Tai site is located on
the top of Mount Tai (36.25∘ N, 117.10∘ E; 1545 m a.s.l.)
in Shandong Province, and it is affected by regional air pollution with limited
impact from local sources. The two cities of Tai'an and Jinan (the capital of
Shandong Province) are 15 and 60 km to the south and north, respectively.
N2O5 and ClNO2 were measured using an iodide-adduct chemical
ionization mass spectrometer (CIMS; THS Instrument, Atlanta), which has been
deployed in several field campaigns (Wang et al., 2016; Tham et al., 2016;
Z. Wang et al., 2017; X. Wang et al., 2017; Yun et al., 2018). The related trace gases (O3, NO, and NO2, etc.), aerosol size distribution, aerosol composition, and meteorological parameters were concurrently measured during
the campaigns. Detailed descriptions of the measurement site and
instrumentation can be found in Yun et al. (2018) and Z. Wang et al. (2017), and the measurement techniques, uncertainties, and detection limits
of the instruments are summarized in Table S1.
The uptake coefficient of N2O5, γN2O5, was derived
from the direct measurement of the loss rate coefficient of N2O5
on ambient aerosols using an aerosol flow tube based on the design by Bertram et al. (2009), with some improvements and coupling with an iterative
box model for polluted environments (Wang et al., 2018). Briefly, the flow
tube consisted of a cylindrical stainless-steel tube of 12.5 cm inner
diameter and 120 cm length, with two 10 cm deep 60∘ tapered caps.
The inner wall of the flow tube was coated with Teflon to reduce the wall
loss of N2O5. The inlet was equipped with parallel sampling pass
ways with one having a filter to remove aerosols. The switch with the stainless-steel valve allows the ambient air, with or without aerosol, to be
introduced into the flow tube. The in-situ-generated N2O5 (4.3 ppbv at 120 mL min-1, produced from the reaction of O3 with excess
NO2) was added to the ambient air after the valves and prior to the
flow tube by a side port. The total flow rate in the flow tube was 4.6 L min-1, corresponding to a residence time of 149 s. During the flow-tube experiments, the N2O5, NO, NO2, O3, particle number and
size distribution, and RH were simultaneously measured at the base of the
flow tube, and ambient NO, NO2, and O3 were also measured at the same time.
An iterative box model considering multiple reactions of production and loss
of N2O5 (Reactions R5–R10) was used to determine the loss rate of
N2O5 in both aerosol and non-aerosol modes (Wang et al., 2018).
R5O3+NO2→NO3+O2,R6NO3+NO2→N2O5,R7O3+NO→NO2+O2,R8NO3+NO→2NO2,R9NO3+VOC→products,R10N2O5+aerosol/wall→products.
The rate constants of Reactions (R5)–(R8) were adopted from Sander et al. (2009), and that of Reaction (R9) was from Atkinson and Arey (2003). With
the constraint of measurement data at the entrance of the flow-tube reactor
in the model, the exit concentrations of NO2, O3, and
N2O5 can be predicted by integrating these reactions. The
N2O5 loss rate coefficient, k10, was adjusted until the
N2O5 concentration predicted by the iterative box model matched
with the measured N2O5 value at the exit. Then the loss rate
coefficient of N2O5 on aerosols surfaces can be determined from
the differences of k10 with or without aerosol, assuming a constant
kwall in both modes. The uptake coefficient of N2O5 on
ambient aerosol is then calculated by
γN2O5=4(k10w/aerosol-k10wo/aerosol)/(cSa).
The k10w/aerosol and k10wo/aerosol are the
N2O5 loss rate coefficients with or without aerosol, c is the
mean molecular speed of N2O5, and Sa is the aerosol surface area. The ambient aerosol surface area density was calculated from the dry particle size distributions corrected with a size-resolved kappa–Köhler
function and ambient RH (Hennig et al., 2005; Liu et al., 2014; Yun et al.,
2018). By assuming an uncertainty of 20 % in the particle number size
distribution introduced by charging efficiency, sizing accuracy, and flow
rate variability (Jiang et al., 2014; Kuang et al., 2016; Wiedensohler et al., 2014), as well as an uncertainty of 15 % for the hygroscopic growth at RH < 90 % (Liu et al., 2014), the uncertainty associated with Sa
measurement was estimated to be approximately 30 %. It has to be noted
that the uncertainty introduced by the particle morphology was not accounted
for here, and thus the reported uncertainty in Sa can be considered a lower limit. In addition, Wang et al. (2018) employed a Monte Carlo approach
to evaluate the uncertainty in γN2O5 determination from
different parameters in the flow-tube system, including mean residence time,
wall loss variability with ambient RH, input N2O5 concentration,
and the variability of ambient NO, NO2, O3, and volatile organic compound (VOC) levels during a measurement cycle. The estimated overall uncertainty in γN2O5 determination was propagated to be 37 % to 40 % at γN2O5 values of around 0.03 and from 34 % to 65 % at γN2O5 values around 0.01 when RH varied from 20 % to 70 % (Wang et al., 2018). The uncertainty would be increased for higher RH conditions, even up to 100 %
for RH ≥ 90 % (Z. Wang et al., 2017).
To obtain a holistic picture of γN2O5 in different
geographic regions of China, field measurement results from three previous
campaigns are also used in the present study. These measurements were
conducted at a subrural site at Wangdu and the same mountain site at Mt.
Tai in 2014, and a mountain site at Mt. Tai Mo Shan in South China in 2016.
All the sites are regionally representative sites, as they are situated in
an area with limited anthropogenic influences (Tham et al., 2016; Z. Wang et
al., 2017; Yun et al., 2018; Wang et al., 2016). Detailed information
on the sampling sites, instrumentation, and the γN2O5 determination approach have been described in previous publications (Wang et al., 2016; Tham et al., 2016; Z. Wang et al., 2017), and site descriptions
are briefly summarized in the Supplement. The locations of all the measurement sites are shown on the map in Fig. 1a. The statistics of the trace gases and PM2.5 measured during the campaigns are summarized in Fig. 1b,
representing general pollution conditions at these sites. The mean
concentration of O3, NOx, and PM2.5 at these sites ranged from 43
to 80 ppbv, 2.4 to 14.5 ppbv, and 9.9 to 80.2 µg m-3,
respectively.
(a) The locations of the four field measurement sites
(star markers) in China. (b) Comparisons of the concentrations of
O3, NOx,
PM2.5, and observed RH and γN2O5 during the five campaigns in China. Squares
represent the median values and bars represent the interquartile ranges of
the values in the five measurements. It should be noted that the high RH in
Mt. Tai in 2014 and Tai Mo Shan campaigns were caused by frequent cloud or fog
events, and the γN2O5 was determined only
during noncloudy periods in these two campaigns.
In addition, the Community Multiscale Air Quality (CMAQ) model (v5.1) was
employed to evaluate the uptake parameterization. Two simulations (default
and revised) were conducted. In the default case, the N2O5 uptake
and ClNO2 production were calculated based on the parameterization by
Bertram and Thornton (2009). In the revised case, the new parameterization
derived in this study was used. Other model configuration options were the same.
The SAPRC07tic gas mechanism and AERO6i aerosol mechanism were used. The Weather
Research and Forecasting (WRF) model (v4.0) was applied to generate the
meteorological inputs for the CMAQ simulations. The anthropogenic emission
inputs were generated based on the local Chinese emission inventory (Zhao et
al., 2018) and the INTEX-B dataset for Asia (Zhang et al., 2009). The
high-resolution chloride emission inventory for China from Fu et al. (2018)
was also included. More details on the model configuration can be found in Fu
et al. (2019). The simulation domain covers China with a resolution of
36km×36 km (Fig. S1), based on a Lambert projection with two true
latitudes of 25 and 40∘ N. The simulation period was
from 1 to 31 December 2017, with 5 d before as a spin-up time.
Relationship between the field-measured or derived N2O5 uptake coefficient γN2O5 and (a) aerosol water content, (b)
particle nitrate, (c)H2O to NO3- molarity ratio, and (d)Cl- to NO3- molarity ratio. Green triangles, red triangles, cyan diamond symbols, orange squares, and blue circles represent the results of Wangdu in 2014, Mount Tai in 2014, Tai Mo Shan in 2016, Heshan in 2017, and Mount Tai in 2018, respectively. The solid lines are linear or exponential regressions.
Results and discussionField-measured γN2O5 and influencing factors
During the field measurements at Heshan and Mt. Tai, the air was
characterized as moderately polluted for O3 (43±22 ppbv at
Heshan and 63±14 ppbv at Mt. Tai), NOx (14.0±11.5 ppbv at
Heshan and 2.2±2.1 ppbv at Mt. Tai), and PM2.5 (66.7±41.9µg m-3 at Heshan and 33.7±26.7µg m-3 at Mt.
Tai), as summarized in Table S2 and shown in Fig. 1b. γN2O5,
which was directly measured using the aerosol flow tube, showed a large
variation ranging from 0.002 to 0.067 with an average of 0.020±0.019
at Heshan and from 0.001 to 0.019 with an average of 0.011±0.005 at
Mt. Tai. These values are within the range of 10-5 to > 0.1
derived from the ambient N2O5 concentrations around the world
(e.g., Brown et al., 2006; Bertram et al., 2009b; Riedel et al., 2012; Morgan
et al., 2015; Z. Wang et al., 2017; Tham et al., 2018; McDuffie et al.,
2018a) but slightly lower than the previous results in the polluted regions
in China (0.021 to 0.102) (Z. Wang et al., 2017; X. Wang et al., 2017; H. Wang et al., 2017). The field-measured γN2O5 and relevant pollutants
at the two sites as well as those derived from three previous studies in China are
summarized in Fig. 1b, covering diverse atmospheric conditions from
moderately humid to humid conditions and from clean to polluted conditions.
Figure 2 shows the relationship between the field-measured γN2O5
and the aerosol composition during five campaigns at those four sites in
China. It can be seen that the γN2O5 had a good positive
correlation with the aerosol water content (r2=0.65) (Fig. 2a),
suggesting a common controlling role of aerosol water in the reactivity of
N2O5 in both northern and southern China. Although the positive
correlation of γN2O5 with the humidity or aerosol water has
been observed in the low range in previous laboratory studies, the γN2O5 reached plateaus at a value around 0.036 at RH > 50 % or [H2O] > 15 M (Hallquist et al., 2003; Thornton et al.,
2003; Bertram and Thornton, 2009). In contrast, other laboratory studies
also measured higher γN2O5 values on NH4HSO4
particles. For example, Mozurkewich and Calvert (1988) reported an upper
limit of γN2O5 of 0.056 at RH = 55 % at 293 K, which
increased to around 0.1 at 274 K. Kane et al. (2001) observed a strong RH-dependent γN2O5, increasing from 0.018 to 0.069 with RH from
56 % to 99 %, which is largely consistent with the field results in the
present study. Moreover, several field measurements also observed γN2O5 values exceeding 0.04 at high RH or water molarity (e.g., Phillips et al., 2016; McDuffie et al., 2018a; H. Wang et al., 2017; Tham et al., 2018), and some of them also found the similar positive relationship between
γN2O5 and water molarity (McDuffie et al., 2018a). Although
uncertainties may exist in the calculation of aerosol surface and uptake
coefficient at high ambient RH conditions, our results with a consistently
increasing trend of γN2O5 with [H2O] from below 10 M up to
50 M suggest that the aerosol water content strongly affects the activity of
N2O5 uptake, and that N2O5 hydrolysis is always limited
by aerosol water content under all the encountered ambient conditions. Since
limited measurement data of γN2O5 from laboratory and field studies
are available at the RH > 80 % condition, it is unclear what exact
mechanism or process (e.g., a phase change different from laboratory-made
particles or acidity involved) promotes more effective uptake on ambient
aerosols at higher aerosol water content conditions. Therefore, more detailed
investigations of N2O5 uptake on nanosized water or aerosol droplets
in the real (or close to real) ambient conditions are clearly warranted. For
nitrate, a clear suppression effect can be found at the Chinese sites (Fig. 2b), which is similar to most of the previous field and laboratory studies. The decrease of γN2O5 with increasing nitrate concentration
seems to be better captured by an “exponential-decay” curve, with almost
linear suppression for [NO3-] below 5 M. The observed γN2O5 under high nitrate condition (> 5 M) was generally
below 0.025 and became nitrate independent as the nitrate levels further
increased.
The γN2O5 variation was affected by the additive effects from both [NO3-] and [H2O], which could not be easily isolated because of their competing reactions with the reactive intermediate H2ONO2+. This is further supported by the positive dependence of γN2O5 on the molar ratio of [H2O]/[NO3-]
(Fig. 2c). Different from the previously reported plateauing of γN2O5 with increasing [H2O]/[NO3-] ratio in laboratory studies (Hallquist et al., 2003; Bertram and Thornton, 2009), no decrease in γN2O5 suppression was found in the present study for [H2O]/[NO3-] ratio of up to 60. The more scattered data at
higher [H2O]/[NO3-] ranges imply that the variation of
γN2O5 becomes more sensitive to other factors in the diluted
aqueous aerosols. Although the γN2O5 measured at two mountain sites showed a positive relationship with [Cl-]/[NO3-], the
overall results from five sites did not exhibit an obvious pattern (Fig. 2d). These results suggest that chloride concentration may not play a
critical role in γN2O5 during our observations as laboratory
studies have observed (Bertram and Thornton, 2009), possibly due to the
complex effect of aerosol mixing state. Though the measured γN2O5 exhibited a nonlinear relationship and complex dependence on different factors at a single site, the general consistent patterns at different sites in this study suggests the feasibility of a common parameterization representing the N2O5 uptake in these regions.
Statistical summary and comparison of the observed
parameters (N2O5 uptake
coefficient, γN2O5; ClNO2 yield, ΦClNO2)
with values predicted from different parameterizations.
ParametersAverage ± SDMaximumMinimumr2γN2O5Observed0.026±0.0240.100.001–BT090.047±0.0150.0750.0210.54BT09 w/o Cl-0.020±0.0180.0580.0010.72Fitted0.026±0.0200.0710.0020.70ΦClNO2Observed0.31±0.271.040.004–BT090.74±0.261.000.200.025Fitted0.57±0.330.990.050.003Comparison to parameterizations
Current regional air quality models such as WRF-Chem and CMAQ mainly use the
γN2O5 parameterization recommended by Bertram and Thornton (2009) (hereafter referred to as BT09), which links γN2O5 to
aerosol water content, nitrate, and chloride as well as the aerosol size and
ambient temperature. The BT09 parameterization based on the abovementioned
reaction mechanism (Reactions R1–R5) was expressed as follows:
2γN2O5=4cVaSaKHk′2f1-1k3H2Ok2bNO3-+1+k4[Cl-]k2b[NO3-],3k′2f=β-βe(-δH2O),
where Va/Sa is the measured aerosol volume to surface area ratio, ranging from 3.30×10-8 to 9.29×10-8 m in the
five campaigns; KH is Henry's law coefficient, taken as 51 (Bertram and Thornton, 2009; Fried et al., 1994); β=1.15×106;
δ=-0.13. The parameters k3/k2b(=0.06) and k4/k2b(=29) represent the relative rates of competing reactions of intermediate
H2ONO2+(aq) with H2O (Reaction R3) and Cl- (Reaction R4) over
NO3- (Reaction R2), respectively. [H2O], [NO3-], and
[Cl-] are the aerosol water content, aerosol nitrate, and chloride
molarity, respectively, calculated by the E-AIM model with the measured
ionic compositions of PM2.5 and RH
(http://www.aim.env.uea.ac.uk/aim/aim.php, last access: 8 April 2020) (Wexler and Clegg, 2002).
We calculate the γN2O5 values from BT09 with the measured
aerosol composition at the five sites. The parameterized γN2O5
ranged from 0.021 to 0.075, with an average of 0.047±0.015, which
overestimates the observed values by a factor of 1.8. When the chloride
effect was excluded, the parameterized γN2O5 mean value
decreased to 0.020±0.018, which was better correlated with but
underestimated (by 30 %) the measurements (Table 1). Figure 3 compares the
observation-derived and parameterized γN2O5 at five sites in
China and in different parts of the world. The BT09 parameterization (blue
markers in Fig. 3) generally overestimates the observed γN2O5
values in the range of 0.001 to 0.03, but it is closer (within a factor of 1.5)
to the observed value for γN2O5 above 0.03 in Germany
(Phillips et al., 2016) and Mt. Tai (Z. Wang et al., 2017). The BT09
parameterization excluding chloride effects (orange markers) gives much
better agreement, with more values located in the range within a factor of
2, though the γN2O5 was still overpredicted in most of the
studies in North America (Bertram et al., 2009b; Riedel et al., 2012;
McDuffie et al., 2018a) except for Boulder (Wagner et al., 2013). The
improvement indicates that the efficiency of chloride in competing for the
H2ONO2+ intermediate and the effects on N2O5 uptake
on ambient aerosols might be overestimated, possibly due to the existence of
other nucleophiles competing with Cl- (McDuffie et al., 2018b; Staudt et al., 2019) or different mixing states of particle and nonuniform
distribution of available chlorine in the aerosols.
Organic matter or coatings on the aerosols can suppress the uptake of
N2O5 (Thornton and Abbatt, 2005; McNeill et al., 2006; Park et
al., 2007), and previous studies have attempted to account for this effect
by treating organics as a coating on the inorganic core (Anttila et al.,
2006; Riemer et al., 2009). However, significant underpredictions were found
from the parameterization of BT09 combined with the organic effect (Morgan
et al., 2015; McDuffie et al., 2018a; Tham et al., 2018) (green and red
markers in Fig. 3). One reason could be that the parameterization does not
differentiate the water-soluble organic fractions and simplifies the
morphology, and phase state, which leads to the underestimation of the
solubility and/or diffusivity of N2O5 in the organics. The complex
effects of organic matter on N2O5 uptake remain poorly quantified
(McDuffie et al., 2018a), and the prediction of composition, morphology and
phase state of the organic fractions are still difficult in current air
quality models. Therefore, we do not consider the organic effect in deriving
a new parameterization in the next section.
Summary of the comparisons of field-measured or derived
γN2O5 and values estimated from
parameterizations from the literature. Blue, orange, green, and red
markers represent the results calculated from parameterizations of original
BT09, BT09 excluding chloride effect, BT09 plus organic effect, and BT09
excluding chloride but with organic effect, respectively.
Observation-based empirical parameterization of γN2O5
Based on the above discussion and comparison, we attempt to derive a new
empirical parameterization of γN2O5 following the BT09
framework (Eq. 2) and using the measurement data from five field campaigns
in China. The variables in the parameterization (i.e., reaction rates) were
fitted with multiple regressions to obtain the best representation of
observations in China. The derived empirical parameterization of γN2O5 is shown as Eq. (4) and the fitted γN2O5 values are
summarized in Table 1.
γN2O5=4cVaSaKH×3.0×104×H2O1-10.033×H2ONO3-+1+3.4×[Cl-][NO3-]
In view of the linear dependence of γN2O5 on the aerosol water content in this study and reaction mechanism (Bertram and Thornton, 2009), the second-order reaction rate coefficient with water (refer to k′2f in
Eqs. 2 and 3) was fitted as a linear function of [H2O], as
(3.0±0.4)×104×[H2O]. This value is in
reasonable agreement with the values of (2.7–3.8) ×104,
∼3.9×104, and 2.6×104 M-1 s-1 determined from ammonium bisulfate, ammonium sulfate (Gaston and Thornton, 2016), and aqueous organic acid particles (Thornton et al., 2003),
respectively. Compared to original BT09 (Eq. 3), the newly fitted
k′2f is smaller for [H2O] < 38 M, but it become higher with the increasing of aerosol water content (Fig. S2). Different dimensionless KH values have been used in previous studies, e.g., ∼ 50
(e.g., Hallquist et al., 2003; Bertram and Thornton, 2009) or
∼ 120 (e.g., Gaston et al., 2014; Gaston and Thornton, 2016; Griffiths et al., 2009), which correspond to a Henry's law constant of 2 or 5 M atm-1 at 298 K. As γN2O5 in the parameterization is linearly dependent
on the KH, an increase of KH value would proportionally increase
the γN2O5 value, but it cannot account for the large variability of measured γN2O5 values. Given the lack of an explicit function of effective Henry's law constant for N2O5 to include the
different processes (e.g., “salting-in” effect and surface processes), we use
the value of 51 suggested by Bertram and Thornton (2009) and enclose those
effects from the aerosol composition in the last “chemical” term. The
derived empirical ratios in the last chemical term not only represent the
competing ratio of these reactions but also include other unspecified
effects or processes (organic coating, mixing state, other
nucleophiles reactions, etc.). The fitted relative rates of competing
reactions, i.e., k3/k2b and k4/k2b, were 0.033±0.017 and 3.4±1.4, respectively, which are smaller than the original
BT09 parameters by factors of 1.8 and 8.5, respectively. The smaller ratios
of the reaction rates indicate a smaller enhancement effect of chloride or a
larger suppression effect by nitrate, which is consistent with the
abovementioned relationship of γN2O5 with the aerosol
composition. Other suppression effects such as organic coating and mixing
state that were not specified in the parameterization also may contribute to,
and are reflected in, the smaller fitted values. As compared in Fig. 4 and
Table 1, the new empirical parameterization can better reproduce the average
values and the large variability of the observed γN2O5 than the
original BT09 both with and without considering Cl- effects.
Comparison of the field-measured or derived γN2O5 with the values estimated from parameterizations
for the five sites in the present study. The dashed line represents the 1 : 1
line. Blue circles, orange triangles, and red squares are results estimated
by BT09 parameterization, BT09 excluding chloride effect and the derived
observation-based empirical parameterization, respectively.
Statistical summary and comparison of the observed species
(nitrate and NO2 concentrations) with values
predicted from different parameterization. NMB represents the normalized
mean bias.
As suggested by the previous studies, the production yield of ClNO2
(ΦClNO2) from N2O5 uptake is also a function of
competing reactions of H2O and Cl- content in aerosols, and they can be
estimated from ΦClNO2=1/(1+k3/k4×[H2O]/[Cl-]) (Bertram and Thornton, 2009). Based on the
abovementioned fitting results for γN2O5, k4/k3 is determined
to be 105±37 for the five sites, which is smaller than the values of
450±100 (Roberts et al., 2009), 483±175 (Bertram and
Thornton, 2009) and 836±32 (Behnke et al., 1997) derived from
laboratory experiments and used in previous parameterizations. As compared
in Fig. S3 and Table 1, although the newly fitted values improve the
estimated ClNO2 yield comparing to the original BT09 (with
k4/k3 of 483), overestimation remains, and the large variability
of observed ΦClNO2 in different campaigns still cannot be well
captured. As shown in Fig. 5, the new fits can better catch the ΦClNO2 trend at [H2O]/[Cl-]>750, but a discrepancy
is still obvious at [H2O]/[Cl-]<750. The discrepancy
could be due to aqueous-phase competition reactions of intermediate
H2ONO2+ with other compounds (e.g., phenol) (Heal et al.,
2007) and ClNO2 loss or reaction mechanisms (e.g., reaction with Cl-
to form Cl2) (Roberts et al., 2008, 2009). A recent laboratory study
(Staudt et al., 2019) has reported that sulfate and acetate can suppress
ΦClNO2 for Cl--containing solutions, but such a sulfate
suppression effect was not observed in our results. Further studies are
needed to identify and quantify these effects for better parameterizing the
heterogeneous ClNO2 production. Nonetheless, the revised
k3/k4 from fitting the field data has improved the estimates
of ΦClNO2 at our study sites.
Relationship between the ClNO2
yield, ΦClNO2, and the molarity ratio of
H2O to Cl-. Gray diamond symbols, blue
circles, and red squares represent the observed ΦClNO2, values from BT09 parameterization, and those fitted
from the empirical parameters derived in the present study, respectively.
Evaluation of the empirical parameterization
To further evaluate the representativeness and validity of the newly fitted
empirical parameterization of γN2O5 in predicting
N2O5 heterogeneous process in air quality models, simulation tests
were performed with the WRF-CMAQ model. The simulations were conducted with
the incorporation of newly fitted and original BT09 parameterizations,
respectively. The simulated concentrations of NO2 and NO3-,
as the key precursor and a product of the N2O5 uptake, were
compared with the observed daily NO3- concentrations at 28 sites
and hourly NO2 concentrations at 472 sites in the North China Plain
during December of 2017. As summarized in Table 2 and shown in Fig. S4, the
simulation with original BT09 parameterization overestimated the regionally
averaged NO3- concentrations by 18.7 % compared to the
observations, whereas the new parameterization gave more consistent results
with the observations (20.98±18.77µg m-3 vs. 20.94±17.16µg m-3), reducing the normalized mean bias (NMB) of
simulated NO3- concentration from 18.72 % to 0.19 %. The
simulated NO2 concentrations were also in better agreement with the
observations, with the NMB changing from -12.25 % to -8.06 %. In
addition to NO2 and NO3-, we also compared the simulated
N2O5 concentrations for December 2017 with those observed in the
wintertime at various locations in China, including two in the North China
Plain (Beijing and Wangdu in Hebei Province) and two in southern China (Tai
Mo Shan and Heshan). As shown in Fig. 6, with the new parameterization,
the WRF-CMAQ model can better simulate the average concentration and
variation range of N2O5 at these locations. Overall, the new
parameterization has significantly reduced the discrepancies between the
modeled and observed concentrations of NO2, N2O5, and
NO3- at our study sites and periods in both northern and
southern China. More tests of this empirical parameterization are warranted
for other locations and seasons in China and other parts of the world.
Comparison of simulated N2O5 concentrations by the
CMAQ model for December 2017 with the wintertime observation results from
four sites in China. The field observations were conducted in Wangdu (Hebei
Province) in December 2017, Beijing in January 2018, Heshan (Guangdong
Province) in January 2017, and Tai Mo Shan (Hong Kong) in November 2013. The
columns and error bars represent the average value and standard deviation,
respectively.
Conclusion
Nitrate is becoming the predominant component of PM2.5 during severe
haze events in China in recent years (Zhang et al., 2015; Li et al., 2018),
and ground-level ozone pollution in urban areas is also worsening (T. Wang et
al., 2017). Despite extensive research, current air quality models still
have difficulties in accurately simulating the N2O5 uptake on
aerosols, which limits their ability to predict the lifetime and fate of
NOx and therefore the production of aerosol nitrate and ozone. Based
on the measurements from five field campaigns at four sites across China
with different atmospheric conditions, our study examined the factors
influencing N2O5 uptake processes and derived an observation-based
empirical parameterization of N2O5 uptake. While further research
is still needed on the additional factors affecting γN2O5 and
ΦClNO2, the empirical parameterization derived here can be used
in air quality models to improve the prediction of PM2.5 and
photochemical pollution in China and similar polluted regions of the world.
Data availability
The data used in this study are available upon request from Zhe Wang
(z.wang@ust.hk) and Tao Wang (cetwang@polyu.edu.hk).
The supplement related to this article is available online at: https://doi.org/10.5194/acp-20-4367-2020-supplement.
Author contributions
TW and ZW designed the study. WW, CY, and ZW designed the aerosol flow tube,
and CY carried out the aerosol flow-tube measurements. MX, TC, PZ, HL, YS,
YZ, and DY conducted the field measurement of relevant species and data
analysis. XF performed the model simulation. CY, ZW, and TW wrote the
article, with discussions and comments from all co-authors.
Competing interests
The authors declare that they have no conflict of interest.
Special issue statement
This article is part of the special issue “Multiphase chemistry of secondary aerosol formation under severe haze”. It is not associated with a conference.
Acknowledgements
The authors would like to acknowledge the Hong Kong Environmental Protection Department for their help with access to the TMS AQM station. The authors greatly acknowledge the editor and anonymous reviewers for their constructive suggestions.
Financial support
This research has been supported by the National Natural Science Foundation of China (grant nos. 91544213 and 91844301) and the Research Grants Council of Hong Kong Special Administrative Region (grant nos. T24/504/17, C5022-14G, and 15265516).
Review statement
This paper was edited by Jingkun Jiang and reviewed by two anonymous referees.
ReferencesAnttila, T., Kiendler-Scharr, A., Tillmann, R., and Mentel, T. F.: On the
Reactive Uptake of Gaseous Compounds by Organic-Coated Aqueous Aerosols:
Theoretical Analysis and Application to the Heterogeneous Hydrolysis of
N2O5, J. Phys. Chem. A, 110, 10435–10443, 10.1021/jp062403c, 2006.Atkinson, R. and Arey, J.: Gas-phase tropospheric chemistry of biogenic
volatile organic compounds: a review, Atmos. Environ., 37, 197–219, 10.1016/s1352-2310(03)00391-1, 2003.Behnke, W., George, C., Scheer, V., and Zetzsch, C.: Production and decay of
ClNO2 from the reaction of gaseous N2O5 with NaCl solution:
Bulk and aerosol experiments, J. Geophys. Res.-Atmos.,
102, 3795–3804, 10.1029/96jd03057, 1997.Bertram, T. H. and Thornton, J. A.: Toward a general parameterization of N2O5 reactivity on aqueous particles: the competing effects of particle liquid water, nitrate and chloride, Atmos. Chem. Phys., 9, 8351–8363, 10.5194/acp-9-8351-2009, 2009.Bertram, T. H., Thornton, J. A., and Riedel, T. P.: An experimental technique for the direct measurement of N2O5 reactivity on ambient particles, Atmos. Meas. Tech., 2, 231–242, 10.5194/amt-2-231-2009, 2009a.Bertram, T. H., Thornton, J. A., Riedel, T. P., Middlebrook, A. M.,
Bahreini, R., Bates, T. S., Quinn, P. K., and Coffman, D. J.: Direct
observations of N2O5 reactivity on ambient aerosol particles,
Geophys. Res. Lett., 36, L19803, 10.1029/2009gl040248, 2009b.
Brown, S., Ryerson, T., Wollny, A., Brock, C., Peltier, R., Sullivan, A.,
Weber, R., Dube, W., Trainer, M., and Meagher, J. F.: Variability in
nocturnal nitrogen oxide processing and its role in regional air quality,
Science, 311, 67–70, 2006.Brown, S. S., Dubé, W. P., Fuchs, H., Ryerson, T. B., Wollny, A. G.,
Brock, C. A., Bahreini, R., Middlebrook, A. M., Neuman, J. A., and Atlas,
E.: Reactive uptake coefficients for N2O5 determined from aircraft
measurements during the Second Texas Air Quality Study: Comparison to
current model parameterizations, J. Geophys. Res.-Atmos., 114, D00F10, 10.1029/2008JD011679, 2009.Brown, S. S., Dubé, W. P., Fuchs, H., Ryerson, T. B., Wollny, A. G.,
Brock, C. A., Bahreini, R., Middlebrook, A. M., Neuman, J. A., Atlas, E.,
Roberts, J. M., Osthoff, H. D., Trainer, M., Fehsenfeld, F. C., and
Ravishankara, A. R.: Reactive uptake coefficients for N2O5
determined from aircraft measurements during the Second Texas Air Quality
Study: Comparison to current model parameterizations, J. Geophys. Res., 114, D00F10, 10.1029/2008jd011679, 2009.
Brown, S. S., Dubé, W. P., Tham, Y. J., Zha, Q., Xue, L., Poon, S.,
Wang, Z., Blake, D. R., Tsui, W., and Parrish, D. D.: Nighttime chemistry at
a high altitude site above Hong Kong, J. Geophys. Res.-Atmos., 121, 2457–2475, 2016.Cosman, L. M., Knopf, D. A., and Bertram, A. K.: N2O5 reactive
uptake on aqueous sulfuric acid solutions coated with branched and
straight-chain insoluble organic surfactants, J. Phys. Chem. A, 112,
2386–2396, 2008.Davis, J. M., Bhave, P. V., and Foley, K. M.: Parameterization of N2O5 reaction probabilities on the surface of particles containing ammonium, sulfate, and nitrate, Atmos. Chem. Phys., 8, 5295–5311, 10.5194/acp-8-5295-2008, 2008.Evans, M. and Jacob, D. J.: Impact of new laboratory studies of
N2O5 hydrolysis on global model budgets of tropospheric nitrogen
oxides, ozone, and OH, Geophys. Res. Lett., 32, L09813, 10.1029/2005GL022469, 2005.Finlayson-Pitts, B. J., Ezell, M. J., and Pitts, J. N.: Formation of
chemically active chlorine compounds by reactions of atmospheric NaCl
particles with gaseous N2O5 and ClONO2, Nature, 337,
241–244, 1989.Fried, A., Henry, B. E., Calvert, J. G., and Mozurkewich, M.: The reaction
probability of N2O5 with sulfuric-acid aerosols at stratospheric
temperatures and compositions, J. Geophys. Res., 99, 3517–3532, 1994.
Fu, X., Wang, T., Wang, S., Zhang, L., Cai, S., Xing, J., and Hao, J.:
Anthropogenic emissions of hydrogen chloride and fine particulate chloride
in China, Environ. Sci. Technol., 52, 1644–1654, 2018.Fu, X., Wang, T., Zhang, L., Li, Q., Wang, Z., Xia, M., Yun, H., Wang, W., Yu, C., Yue, D., Zhou, Y., Zheng, J., and Han, R.: The significant contribution of HONO to secondary pollutants during a severe winter pollution event in southern China, Atmos. Chem. Phys., 19, 1–14, 10.5194/acp-19-1-2019, 2019.Gaston, C. J. and Thornton, J. A.: Reacto-diffusive length of
N2O5 in aqueous sulfate-and chloride-containing aerosol particles,
J. Phys. Chem. A, 120, 1039–1045, 2016.Gaston, C. J., Thornton, J. A., and Ng, N. L.: Reactive uptake of N2O5 to internally mixed inorganic and organic particles: the role of organic carbon oxidation state and inferred organic phase separations, Atmos. Chem. Phys., 14, 5693–5707, 10.5194/acp-14-5693-2014, 2014.Griffiths, P. T., Badger, C. L., Cox, R. A., Folkers, M., Henk, H. H., and
Mentel, T. F.: Reactive uptake of N2O5 by aerosols containing
dicarboxylic acids. Effect of particle phase, composition, and nitrate
content, J. Phys. Chem. A, 113, 5082–5090, 2009.Hallquist, M., Stewart, D. J., Stephenson, S. K., and Anthony Cox, R.:
Hydrolysis of N2O5 on sub-micron sulfate aerosols, Phys.
Chem. Chem. Phys., 5, 3453–3463, 10.1039/b301827j, 2003.Heal, M. R., Harrison, M. A. J., and Neil Cape, J.: Aqueous-phase nitration
of phenol by N2O5 and ClNO2, Atmos. Environ., 41,
3515–3520, 10.1016/j.atmosenv.2007.02.003, 2007.Hennig, T., Massling, A., Brechtel, F. J., and Wiedensohler, A.: A Tandem
DMA for highly temperature-stabilized hygroscopic particle growth
measurements between 90 % and 98 % relative humidity, J. Aerosol
Sci., 36, 1210–1223, 10.1016/j.jaerosci.2005.01.005, 2005.
Jiang, J., Kim, C., Wang, X., Stolzenburg, M. R., Kaufman, S. L., Qi, C.,
Sem, G. J., Sakurai, H., Hama, N., and McMurry, P. H.: Aerosol Charge
Fractions Downstream of Six Bipolar Chargers: Effects of Ion Source, Source
Activity, and Flowrate, Aerosol Sci. Technol., 48, 1207–1216, 2014.Kane, S. M., Caloz, F., and Leu, M.-T.: Heterogeneous uptake of gaseous
N2O5 by (NH4)2SO4, NH4HSO4, and
H2SO4 aerosols, J. Phys. Chem. A, 105,
6465–6470, 2001.
Kuang, C.: TSI Model 3936 scanning mobility particle spectrometer instrument
handbook, ARM Climate Research Facility, Washington, DC, USA,
2016.Li, H., Zhang, Q., Zheng, B., Chen, C., Wu, N., Guo, H., Zhang, Y., Zheng, Y., Li, X., and He, K.: Nitrate-driven urban haze pollution during summertime over the North China Plain, Atmos. Chem. Phys., 18, 5293–5306, 10.5194/acp-18-5293-2018, 2018.Li, Q., Zhang, L., Wang, T., Tham, Y. J., Ahmadov, R., Xue, L., Zhang, Q., and Zheng, J.: Impacts of heterogeneous uptake of dinitrogen pentoxide and chlorine activation on ozone and reactive nitrogen partitioning: improvement and application of the WRF-Chem model in southern China, Atmos. Chem. Phys., 16, 14875–14890, 10.5194/acp-16-14875-2016, 2016.Liu, H. J., Zhao, C. S., Nekat, B., Ma, N., Wiedensohler, A., van Pinxteren, D., Spindler, G., Müller, K., and Herrmann, H.: Aerosol hygroscopicity derived from size-segregated chemical composition and its parameterization in the North China Plain, Atmos. Chem. Phys., 14, 2525–2539, 10.5194/acp-14-2525-2014, 2014.McDuffie, E. E., Fibiger, D. L., Dubé, W. P., Lopez-Hilfiker, F., Lee,
B. H., Thornton, J. A., Shah, V., Jaeglé, L., Guo, H., and Weber, R. J.:
Heterogeneous N2O5 uptake during winter: Aircraft measurements
during the 2015 WINTER campaign and critical evaluation of current
parameterizations, J. Geophys. Res.-Atmos., 123,
4345–4372, 2018a.McDuffie, E. E., Fibiger, D. L., Dubé, W. P., Lopez Hilfiker, F., Lee,
B. H., Jaeglé, L., Guo, H., Weber, R. J., Reeves, J. M., and Weinheimer,
A. J.: ClNO2 yields from aircraft measurements during the 2015 WINTER
campaign and critical evaluation of the current parameterization, J. Geophys. Res.-Atmos., 123, 12994–13015, 2018b.McNeill, V. F., Patterson, J., Wolfe, G. M., and Thornton, J. A.: The effect of varying levels of surfactant on the reactive uptake of N2O5 to aqueous aerosol, Atmos. Chem. Phys., 6, 1635–1644, 10.5194/acp-6-1635-2006, 2006.Morgan, W. T., Ouyang, B., Allan, J. D., Aruffo, E., Di Carlo, P., Kennedy, O. J., Lowe, D., Flynn, M. J., Rosenberg, P. D., Williams, P. I., Jones, R., McFiggans, G. B., and Coe, H.: Influence of aerosol chemical composition on N2O5 uptake: airborne regional measurements in northwestern Europe, Atmos. Chem. Phys., 15, 973–990, 10.5194/acp-15-973-2015, 2015.Mozurkewich, M. and Calvert, J. G.: Reaction probability of N2O5
on aqueous aerosols, J. Geophys. Res.-Atmos., 93,
15889–15896, 1988.
Osthoff, H. D., Roberts, J. M., Ravishankara, A., Williams, E. J., Lerner,
B. M., Sommariva, R., Bates, T. S., Coffman, D., Quinn, P. K., and Dibb, J.
E.: High levels of nitryl chloride in the polluted subtropical marine
boundary layer, Nat. Geosci., 1, 324–328, 2008.Park, S.-C., Burden, D. K., and Nathanson, G. M.: The inhibition of
N2O5 hydrolysis in sulfuric acid by 1-butanol and 1-hexanol
surfactant coatings, J. Phys. Chem. A, 111, 2921–2929,
2007.Phillips, G. J., Thieser, J., Tang, M., Sobanski, N., Schuster, G., Fachinger, J., Drewnick, F., Borrmann, S., Bingemer, H., Lelieveld, J., and Crowley, J. N.: Estimating N2O5 uptake coefficients using ambient measurements of NO3, N2O5, ClNO2 and particle-phase nitrate, Atmos. Chem. Phys., 16, 13231–13249, 10.5194/acp-16-13231-2016, 2016.Riedel, T. P., Bertram, T. H., Ryder, O. S., Liu, S., Day, D. A., Russell, L. M., Gaston, C. J., Prather, K. A., and Thornton, J. A.: Direct N2O5 reactivity measurements at a polluted coastal site, Atmos. Chem. Phys., 12, 2959–2968, 10.5194/acp-12-2959-2012, 2012.Riemer, N., Vogel, H., Vogel, B., Anttila, T., Kiendler-Scharr, A., and
Mentel, T. F.: Relative importance of organic coatings for the heterogeneous
hydrolysis of N2O5 during summer in Europe, J. Geophys. Res., 114, D17307, 10.1029/2008jd011369, 2009.Roberts, J. M., Osthoff, H. D., Brown, S. S., and Ravishankara, A. R.:
N2O5 Oxidizes Chloride to Cl2 in Acidic Atmospheric Aerosol,
Science, 321, 1059–1059, 10.1126/science.1158777, 2008.Roberts, J. M., Osthoff, H. D., Brown, S. S., Ravishankara, A. R., Coffman,
D., Quinn, P., and Bates, T.: Laboratory studies of products of
N2O5 uptake on Cl- containing substrates, Geophys.
Res. Lett., 36, L20808, 10.1029/2009gl040448, 2009.
Sander, S. P., Friedl, R., Barker, J., Golden, D., Kurylo, M.,Wine,
P.,Abbatt, J., Burkholder, J., Kolb, C., and Moortgat, G.: Chemical kinetics
and photochemical data for use in Atmospheric Studies Evaluation Number 16:
supplement to Evaluation 15: update of key reactions, Jet Propulsion
Laboratory, National Aeronautics and Space Administration, Pasadena, CA,
USA, 2009.Schweitzer, F., Mirabel, P., and George, C.: Multiphase chemistry of
N2O5, ClNO2, and BrNO2, J. Phys. Chem. A, 102,
942–3952, 1998.Staudt, S., Gord, J. R., Karimova, N. V., McDuffie, E. E., Brown, S. S.,
Gerber, R. B., Nathanson, G. M., and Bertram, T. H.: Sulfate and Carboxylate
Suppress the Formation of ClNO2 at Atmospheric Interfaces, ACS Earth Space Chem., 3, 1987–1997, 10.1021/acsearthspacechem.9b00177, 2019.Tham, Y. J., Wang, Z., Li, Q., Yun, H., Wang, W., Wang, X., Xue, L., Lu, K., Ma, N., Bohn, B., Li, X., Kecorius, S., Größ, J., Shao, M., Wiedensohler, A., Zhang, Y., and Wang, T.: Significant concentrations of nitryl chloride sustained in the morning: investigations of the causes and impacts on ozone production in a polluted region of northern China, Atmos. Chem. Phys., 16, 14959–14977, 10.5194/acp-16-14959-2016, 2016.Tham, Y. J., Wang, Z., Li, Q., Wang, W., Wang, X., Lu, K., Ma, N., Yan, C., Kecorius, S., Wiedensohler, A., Zhang, Y., and Wang, T.: Heterogeneous N2O5 uptake coefficient and production yield of ClNO2 in polluted northern China: roles of aerosol water content and chemical composition, Atmos. Chem. Phys., 18, 13155–13171, 10.5194/acp-18-13155-2018, 2018.Thornton, J. A., Braban, C. F., and Abbatt, J. P. D.: N2O5
hydrolysis on sub-micron organic aerosols: the effect of relative humidity,
particle phase, and particle size, Phys. Chem. Chem. Phys., 5,
4593–4603, 10.1039/B307498F, 2003.Thornton, J. A. and Abbatt, J. P. D.: N2O5 Reaction on Submicron
Sea Salt Aerosol: Kinetics, Products, and the Effect of Surface Active
Organics, J. Phys. Chem. A, 109, 10004–10012, 10.1021/jp054183t, 2005.
Thornton, J. A., Kercher, J. P., Riedel, T. P., Wagner, N. L., Cozic, J.,
Holloway, J. S., Dubé, W. P., Wolfe, G. M., Quinn, P. K., and
Middlebrook, A. M.: A large atomic chlorine source inferred from
mid-continental reactive nitrogen chemistry, Nature, 464, 271–274, 2010.Wagner, N., Riedel, T., Young, C., Bahreini, R., Brock, C., Dubé, W.,
Kim, S., Middlebrook, A., Öztürk, F., and Roberts, J.:
N2O5 uptake coefficients and nocturnal NO2 removal rates
determined from ambient wintertime measurements, J. Geophys. Res.-Atmos., 118, 9331–9350, 2013.Wahner, A., Mentel, T. F., Sohn, M., and Stier, J.: Heterogeneous reaction of N2O5 on sodium nitrate aerosol, J. Geophys. Res.-Atmos., 1033, 31103–31112, 1998.Wang, H., Lu, K., Chen, X., Zhu, Q., Chen, Q., Guo, S., Jiang, M., Li, X.,
Shang, D., and Tan, Z.: High N2O5 concentrations observed in urban
Beijing: Implications of a large nitrate formation pathway, Environ.
Sci. Technol. Lett. 4, 416–420, 2017.
Wang, T., Tham, Y. J., Xue, L., Li, Q., Zha, Q., Wang, Z., Poon, S. C.,
Dubé, W. P., Blake, D. R., and Louie, P. K.: Observations of nitryl
chloride and modeling its source and effect on ozone in the planetary
boundary layer of southern China, J. Geophys. Res.-Atmos., 121, 2476–2489, 2016.
Wang, T., Xue, L., Brimblecombe, P., Lam, Y. F., Li, L., and Zhang, L.:
Ozone pollution in China: A review of concentrations, meteorological
influences, chemical precursors, and effects, Sci. Total
Environ., 575, 1582–1596, 2017.Wang, W., Wang, Z., Yu, C., Xia, M., Peng, X., Zhou, Y., Yue, D., Ou, Y., and Wang, T.: An in situ flow tube system for direct measurement of N2O5 heterogeneous uptake coefficients in polluted environments, Atmos. Meas. Tech., 11, 5643–5655, 10.5194/amt-11-5643-2018, 2018.Wang, X., Wang, H., Xue, L., Wang, T., Wang, L., Gu, R., Wang, W., Tham, Y.
J., Wang, Z., and Yang, L.: Observations of N2O5 and ClNO2 at
a polluted urban surface site in North China: High N2O5 uptake
coefficients and low ClNO2 product yields, Atmos. Environ.,
156, 125–134, 2017.Wang, Z., Wang, W., Tham, Y. J., Li, Q., Wang, H., Wen, L., Wang, X., and Wang, T.: Fast heterogeneous N2O5 uptake and ClNO2 production in power plant and industrial plumes observed in the nocturnal residual layer over the North China Plain, Atmos. Chem. Phys., 17, 12361–12378, 10.5194/acp-17-12361-2017, 2017.Wexler, A. S. and Clegg S. L.: Atmospheric aerosol models for systems
including the ions H+, NH4+, Na+, SO42-,
NO3-, Cl-, Br-, and H2O, J. Geophys. Res., 107, D14, 10.1029/2001jd000451, 2002.Wiedensohler, A., Birmili, W., Nowak, A., Sonntag, A., Weinhold, K., Merkel, M., Wehner, B., Tuch, T., Pfeifer, S., Fiebig, M., Fjäraa, A. M., Asmi, E., Sellegri, K., Depuy, R., Venzac, H., Villani, P., Laj, P., Aalto, P., Ogren, J. A., Swietlicki, E., Williams, P., Roldin, P., Quincey, P., Hüglin, C., Fierz-Schmidhauser, R., Gysel, M., Weingartner, E., Riccobono, F., Santos, S., Grüning, C., Faloon, K., Beddows, D., Harrison, R., Monahan, C., Jennings, S. G., O'Dowd, C. D., Marinoni, A., Horn, H.-G., Keck, L., Jiang, J., Scheckman, J., McMurry, P. H., Deng, Z., Zhao, C. S., Moerman, M., Henzing, B., de Leeuw, G., Löschau, G., and Bastian, S.: Mobility particle size spectrometers: harmonization of technical standards and data structure to facilitate high quality long-term observations of atmospheric particle number size distributions, Atmos. Meas. Tech., 5, 657–685, 10.5194/amt-5-657-2012, 2012.
Yun, H., Wang, W., Wang, T., Xia, M., Yu, C., Wang, Z., Poon, S. C. N., Yue, D., and Zhou, Y.: Nitrate formation from heterogeneous uptake of dinitrogen pentoxide during a severe winter haze in southern China, Atmos. Chem. Phys., 18, 17515–17527, 10.5194/acp-18-17515-2018, 2018.Zhang, Q., Streets, D. G., Carmichael, G. R., He, K. B., Huo, H., Kannari, A., Klimont, Z., Park, I. S., Reddy, S., Fu, J. S., Chen, D., Duan, L., Lei, Y., Wang, L. T., and Yao, Z. L.: Asian emissions in 2006 for the NASA INTEX-B mission, Atmos. Chem. Phys., 9, 5131–5153, 10.5194/acp-9-5131-2009, 2009.Zhang, R., Wang, G., Guo, S., Zamora, M. L., Ying, Q., Lin, Y., Wang, W.,
Hu, M., and Wang, Y.: Formation of Urban Fine Particulate Matter, Chem.
Rev., 115, 3803–3855, 10.1021/acs.chemrev.5b00067, 2015.Zhao, B., Zheng, H., Wang, S., Smith, K. R., Lu, X., Aunan, K., Gu, Y.,
Wang, Y., Ding, D., and Xing, J.: Change in household fuels dominates the
decrease in PM2.5 exposure and premature mortality in China in
2005–2015, P. Natl. Acad. Sci. USA, 115, 12401–12406, 2018.