Kinetics, SOA yields and chemical composition of secondary organic aerosol from β-caryophyllene ozonolysis with and without nitrogen oxides between 213 and 313 K

Abstract. β-caryophyllene (BCP) is one of the most important sesquiterpenes (SQTs) in the atmosphere, with a large potential contribution to secondary organic aerosol (SOA) formation mainly from reactions with ozone (O3) and nitrate radicals (NO3). In this work, we study the temperature dependence of the kinetics of BCP ozonolysis, SOA yields, and SOA chemical composition in the dark and in the absence and presence of nitrogen oxides including nitrate radicals (NO3). We cover a temperature range of 213 K – 313 K, representative of tropospheric conditions. The oxidized components in both gas and particle phases were characterized on a molecular level by a Chemical Ionization Mass Spectrometer equipped with a Filter Inlet for Gases and AEROsols using iodide as the reagent ion (FIGAERO-iodide-CIMS). The batch mode experiments were conducted in the 84.5 m3 aluminium simulation chamber AIDA at the Karlsruhe Institute of Technology (KIT). In the absence of nitrogen oxides, the temperature-dependent rate coefficient of the endocyclic double bond in BCP reacting with ozone between 243 – 313 K are negatively correlated with temperature, corresponding to the following Arrhenius equation: k = (1.6 ± 0.4)  × 10−15 × exp((559 ± 97)/T). The SOA yields increase from 16 ± 5 % to 37 ± 11% with temperatures decreasing from 313 K to 243 K at a total organic particle mass of 10 µg m−3. The variation of the ozonolysis temperature leads to substantial impact on the abundance of individual organic molecules. In the absence of nitrogen oxides, monomers C14-15H22-24O3-7 (37.4 %), dimers C28-30H44-48O5-9 (53.7 %) and trimers C41-44H62-66O9-11 (8.6 %) are abundant in the particle phase at 213 K. At 313 K, we observed more oxidized monomers (mainly C14-15H22-24O6-9, 67.5 %) and dimers (mainly C27-29H42-44O9-11, 27.6 %), including highly oxidized molecules (HOMs, C14H22O7,9, C15H22O7,9 C15H24O7,9) which can be formed via hydrogen shift mechanisms, but no significant trimers. In presence of nitrogen oxides, the organonitrate fraction increased from 3 % at 213 K to 12 % and 49 % at 243 K and 313 K, respectively. Most of the organonitrates were monomers with C15 skeletons and only one nitrate group. Higher oxygenated organonitrates were observed at higher temperatures, with their signal-weighted O : C atomic ratio increasing from 0.41 to 0.51 from 213 K to 313 K. New dimeric and trimeric organic species without nitrogen atoms (C20, C35) were formed in presence of nitrogen oxides at 298–313 K indicating potential new reaction pathways. Overall, our results show that increasing temperatures lead to a relatively small decrease of the rate coefficient of the endocyclic double bond in BCP reacting with ozone, but to a strong decrease in SOA yields. In contrast, the formation of HOMs and organonitrates increases significantly with temperature.


can be modified between close to zero to up to 100% and even supersaturated conditions (Möhler et al., 2003).
Water vapor is measured in situ by a tuneable diode laser (TDL) hygrometer with an accuracy of ±5% and a calibrated reference dew point mirror hygrometer (MBW373LX, MBW Calibration Ltd.) with an accuracy of ±1% 120 (Fahey et al., 2014).
The results presented in this work are from dark BCP ozonolysis experiments with or without addition of NO2 from a campaign in November and December 2019 covering five different temperatures between 213 -313 K.
The experimental conditions are listed in Table 1. Two additional experiments were undertaken in March 2020 to study the rate coefficients of BCP reacting with ozone at 243 K and 258 K. BCP (98%, Carl Roth GmbH) was 125 added to the AIDA chamber with a flow of 0.01 m 3 /min of synthetic air saturated with its vapour at 298K. Please note that the BCP concentrations for the experiments at 213 K could not be measured due to the low vapour pressure and strong wall losses at lower temperatures (more details are given in section 2.2). Ozone was in all experiments typically in excess and generated by a silent discharge generator (Semozon 030.2, Sorbios) in pure oxygen (99.9999%). The relative humidity ranged from 96% to 13% for experiments at 213 K and 313 K, 130 respectively. This corresponds to water vapor concentrations of 1 Pa (3.4 ×10 14 cm -3 ) at 213 K and 952 Pa (2.2 ×10 17 cm -3 ) at 313 K, respectively, and reflects the variability of the water vapour concentrations throughout the troposphere. At the initial phase of each experiment, BCP was depleted completely by ozonolysis and SOA was formed. The corresponding conditions are marked as 1a-5a in Table 1. Subsequently, NO2 (1000 ppm of 99.5% purity in nitrogen 99.999%, Basi Schöberl GmbH) was added to the reaction mixture still containing an excess of 135 ozone. A second step of SOA formation was then initialized by adding more BCP. This series of experiments is marked as 1b-5b in Table 1. Hence, the BCP and ozone concentrations listed in Table 1 for experiments 1b-5b include also the amounts added in experiments 1a-5a. Ozone was at nearly the same concentrations as for the initial experiments without NO2, except for the experiments at 273 K. To get a slower decay of BCP to better determine its rate coefficient at 273K, we added 73 ppb ozone into the chamber first, and then added more ozone for detecting the low-oxygenated organic molecules in both gas and particle phases. This alternating measurement mode included 3-min HEPA filter measurement for the particle background, 5-min CHARON particle measurement, 1-min transition for instrument equilibration, 5-min of VOC measurement and another 1-min transition. The CHARON-PTR-MS measured the particle phase at a sampling flow of 500 SCCM via a 1/4" 160 silcosteel tube, while the gas phase was measured at a flowrate of 100 SCCM via a 1/16" PEEK tube taken from the particle measurement flow. Furthermore, a flowrate of 3.9 l/min was added to the total flow to minimize the residence time in the sampling tube. For measuring gases, the drift tube of the PTR-MS was kept at 393 K and 2.8 mbar leading to an electric field (E/N) of 127 Td. During alternating measurements, the drift tube was automatically optimized to 100 Td for particle measurement. BCP was calibrated using a liquid calibration unit 165 (LCU-a, Ionicon Analytic GmbH). The PTR-ToF-MS at an E/N of 127 Td showed significant fragmentation of BCP, in agreement with previous studies (Kim et al., 2009;Kari et al., 2018). In this study, we observed that the parent ion (m/z 205.20, C15H25 + ) contributed (29 ± 1) % to total signals of BCP-related ions including m/z 81.07, m/z 95.09, m/z 109.10, m/z 121.10, m/z 137.13, m/z 149.13 and m/z 205.20 (Fig. S1). Therefore, we scaled the concentration of m/z 205.20 (C15H25 + ) by a factor of 3.45 for the quantification of BCP. The total uncertainty of 170 BCP quantification was estimated as ±20% by including all errors mainly related to the uncertainties of the LCU and the fragmentation pattern of BCP.
Particle size distributions and number concentrations were measured by a scanning mobility particle sizer (SMPS) utilizing a differential mobility analyzer (DMA, 3071 TSI Inc.) connected to a CPC (3772, TSI Inc.). Particle number concentrations were measured by two condensation particle counters (3022a and 3776, TSI Inc.). The 175 particle number size distributions of the SMPS were corrected for the total number concentration measured by a calibrated CPC and used to calculate the SOA mass concentration by applying an effective particle density. This particle density was determined by comparing the mobility and aerodynamic size distributions measured by SMPS and AMS, calculated increasing from 0.9±0.1 at 243K to 1.1 ± 0.1 at 313K, respectively .
A High Resolution-Time-of-Flight-Aerosol Mass Spectrometer (HR-ToF-AMS, Aerodyne Inc.) was used to 180 continuously measure the total organic particle mass with a time resolution of 30 seconds at a total flow rate of 0.0011 m 3 /min (with only 0.0008 m 3 /min going into the instrument). The data was analyzed using the PIKA v1.60C software. For calculation of the organic particle concentration from the AMS mass spectra, a collection efficiency of 0.6 (determined by comparison with the SMPS results) and an ionization efficiency of 1.52 × 10 -7 (calibrated with 300 nm ammonium nitrate particles) were used. K with a total desorption time of 35 minutes (Huang et al., 2018). The data analysis was done with the Tofware software (version 3.1.2). Note that the reagent ion I-(m/z = 126.9) was subtracted from the mass-to-charge ratio of all the molecules shown in this work. For the comparison of measured total particle mass concentration between AMS, SMPS and FIGAERO-iodide-CIMS, we use the maximum sensitivity of 22 cps ppt -1 to convert the signals 200 to mass concentration (Lee et al., 2014;Lopez-Hilfiker et al., 2016). In addition, we did a mass calibration for βcaryophyllinic acid (95%, Toronto Research Chemicals) resulting in a sensitivity of (2.4 −0.63 +0.96 ) cps ppt -1 (details are given in Fig. S2).
Typically, background measurements for both gas and particle phase were done before and after the first addition of BCP to identify any contamination inside the chamber. However, gas background levels were almost negligible 205 for most experiments and most of the particle background signals were from filter matrix contaminations mainly due to fluorinated constituents.

Rate coefficient calculation
Based on the PTR-MS measurements of the BCP decay as well as the ozone measurements, the rate coefficients of the reaction of BCP with ozone can be determined. As BCP has two double bonds with reactivities with ozone 210 differing by a factor of 100 , here we discuss only the rate coefficient for the reaction of the most reactive endocyclic double bond. Since we did not use an OH radical scavenger, the reaction between BCP and OH radicals, which are generated from BCP ozonolysis, was included in our analysis. Employing the following reaction scheme, the observed decays of ozone and BCP were fitted by adjusting only the rate for reaction R1. 215 For the reaction of OH radicals with BCP, the rate coefficient of (1.97±0.25)×10 -10 cm 3 molecule -1 determined for 296 K Winterhalter et al., 2009) was used for all temperatures due to the lack of its temperature dependence. 220 To integrate this simple model and to fit the rate coefficient for reaction R1 we used the software KinSim (Kinetics Simulator for Chemical-Kinetics and Environmental-Chemistry Teaching, version 4.14) (Peng and Jimenez, 2019). The OH radical yields (γ in R1) varied between 5-15% at different temperatures (see section 3.1).

SOA yields calculation
The SOA yields (YSOA) were calculated as YSOA=ΔMorg/ΔVOC, where ΔMorg is the SOA mass formed from the 225 reacted mass of BCP (ΔVOC). Similarly, the yields (YBCA) of BCA, the typical product of BCP ozonolysis, were calculated as YBCA= ΔMBCA/ΔVOC, where ΔMBCA is the mass concentration of β-caryophyllinic acid formed from the reacted mass of BCP (ΔVOC). We used a more than 5-fold ozone excess in this study for all temperatures to facilitate oxidation of all double bonds in BCP and its oxidation products. This should lead to more comparable yields for all conditions studied (Li et al., 2011;Chen et al., 2012). Wall losses of particles and semi volatile trace 230 gases were calculated with the aerosol dynamic model COSIMA (Naumann, 2003;) and used to correct the yields. The yields were calculated for the initial period of the experiments, which lasted about 90 minutes. During this relatively short time period and due to the large size of the simulation chamber, particle https://doi.org/10.5194/acp-2021-1067 Preprint. Discussion started: 6 January 2022 c Author(s) 2022. CC BY 4.0 License. losses contributed typically 6% or less to the total SOA mass. Due to the relatively small particle sizes at the beginning of the experiments, diffusional losses dominated. 235

Results and discussion
In this chapter we discuss the typical course of the experiments, the kinetics of the reaction of BCP with ozone, the SOA mass yields, as well as the SOA chemical composition in absence and in presence of nitrogen oxides. Figure 2 shows the evolution of trace gases as well as particle mass and size distribution for BCP ozonolysis at 240 298K first without and then in presence of nitrogen oxides in experiment 4a and 4b. The time point when ozone was firstly added is regarded as the start of each experiment and is set to zero. As shown in Fig. 2, following the nucleation, the particle size increased to 36 nm and grew further to 57 nm and 69 nm after subsequent additions of ozone and BCP, and finally to 122 nm after NO2 addition. The particle mass increased in presence of the low initial ozone concentration (25 ppb) and stabilized within 20 minutes after increasing the ozone level to above 300 245 ppb reaching 13.3 μg m -3 . A second addition of more BCP led to another increase of the particle mass stabilizing at a level of 17.0 µg m -3 . To this SOA, 42 ppb of NO2 were added, which reacted with the excess of ozone forming NO3 radicals and consequently led to a small increase in particle size and mass (1.9 nm and 0.9 µg m -3 , respectively) due to their reaction with BCP oxidation products. After the third addition of BCP to the reaction mixture, the SOA mass concentration increased to 50.6 μg m -3 . For the other four temperatures, these values are given in Table  250 1. During the final addition of BCP, the existing particles grew quickly and new particle formation were observed.

Overview of the experiments and kinetics of BCP ozonolysis
The discrepancy in mass concentrations obtained from SMPS and HR-TOF-AMS in the initial phase of the experiment are due to the fact that smaller particles are poorly detected by the HR-TOF-AMS due to the lower transmission of sub-100nm particles in the aerodynamic lens (Liu et al., 2007;Williams et al., 2013). After 160 minutes, the particle size reached 122 nm and both mass concentrations agreed well assuming a collection 255 efficiency of 0.6 for the AMS. Please note that the FIGAERO-iodide-CIMS is sensitive to more polar oxidized compounds, thus, the sum of all compounds detected by CIMS can only be a fraction of the total organic aerosol compounds measured by HR-TOF-AMS. On average 36-61 % of the total organic mass concentration was detected by FIGAERO-iodide-CIMS.
After the first addition of an excess of ozone, BCP was depleted within less than 5 minutes. An example of the 260 kinetic model results for the experiment at 313 K is compared to the measured data in Fig. S3 and all kinetic parameters fitted are listed in Table S2. The OH radical yields from the ozonolysis reaction increase from (5±2) % at 243 K to (15±2) % at 313K, and 91-92% of the BCP are calculated to react with ozone under 243-313K. Figure 3 shows the temperature dependence of the rate coefficients for BCP ozonolysis. The rate coefficient we determined for 298 K of (1.09±0.21) × 10 -14 cm 3 molecule -1 s -1 agrees very well with values from Shu and Atkinson 265 (1994) of (1.16 ± 0.43) × 10 -14 cm 3 molecule -1 s -1 and  of (1.1± 0.3) × 10 -14 cm 3 molecule -1 s -1 for 296 K. At lower temperatures, the rate coefficient increases. This is in an agreement with the densityfunctional theory (DFT) quantum chemical calculations by   to a reaction enthalpy of (5.6±1.0) KJ mol -1 in our analysis. Please note that the experiment at 273 K was not used 270 for this analysis because of an unusual background signal in the PTR-MS measurement (Fig. S5b). Figure 4 presents the yields from BCP ozonolysis in the absence of NO2 as a function of the temperature for a constant total organic particle mass concentration (Morg) of 10 µg m -3 . The SOA yields decrease with increasing temperatures from 243K to 313K. For this organic particle mass concentration, we determined a SOA yield of 275 (19.4±6) % at 298K, which was lower by around 55% and 40% than those reported by Chen et al., (2012) and

Particle mass yields
Tasoglou and Pandis (2015), respectively, for a similar particle mass. However, the results are still within the combined uncertainty limits. Please note that these two previous studies used OH radical scavengers, which should lead to lower yields, since OH radicals may oxidize potentially more VOCs causing higher SOA yields. The temperature dependence we observed is significantly lower than e.g. for α-pinene ) and hence 280 reflects the generally lower vapour pressure of the condensable oxidation products compared to the monoterpene.
In our study, the SOA formation time of about 90 minutes was longer than the typical lifetime of the firstgeneration products from BCP ozonolysis (20 minutes) at an ozone level of 300 ppb, thus the difference cannot be explained by potential incomplete reactions. Different initial ozone levels may also contribute to the higher yields reported by Chen et al., (2012) and Tasoglou and Pandis (2015). 285 An overview of the SOA yields determined by Lee et al., 2006, Chen et al., 2012and Tasoglou and Pandis (2015 is given in Fig. S4 in comparison with our results in the temperature range between 243 and 313 K. The SOA masses formed reflect the different oxidation products of differing volatilities  formed at low and high temperatures, which will be discussed in the following section.

Chemical characterization of SOA from BCP ozonolysis without nitrogen oxides 290
In this section the gas and particle phase molecular composition will be discussed mainly based on the FIGAEROiodide-CIMS mass spectra, complemented by the CHARON-PTR-MS. Figure 5 shows the averaged gas-phase mass spectra for all five temperatures in the range 213-313 K, before adding NO2 and when the SOA concentration was in a relatively stable state. Only compounds with mass-to-295 charge ratios less than 400 Th contributed significantly to the FIGAERO-iodide-CIMS spectra. The signals were normalized to the total gas-phase CxHyOz compounds at each temperature. In the temperature range of 213 -273 K, C15H24O3 (likely β-caryophyllonic acid), C15H24O4 (likely β-hydroxycaryophyllonic acid), C15H26O4 (not identified yet), C14H22O4 (β-nocaryophyllonic acid or β-caryophyllinic acid) were the most dominant monomeric compounds in the gas phase. These compounds have been identified as products from BCP ozonolysis at room 300 temperature in previous studies (Jaoui et al., 2003;Winterhalter et al., 2009;Chan et al., 2011;Li et al., 2011). In addition, we also observed several abundant ions, such as C14H20O2, C15H22O2 and C14H20O3, in the PTR-MS mass spectra (Fig. S5). As mentioned above, the PTR-MS is more sensitive to less-oxygenated organic compounds and is prone to fragmentation via e.g. losing H2O. In combination with FIGAERO-iodide-CIMS data, it is reasonable to interpret that C15H22O2 in PTR-MS mass spectra is most likely the fragmentation ion from C15H24O3 via losing 305 H2O. Besides, C15H24O2 and its potential fragmentation ion C15H22O could be tentatively identified as BCP https://doi.org/10.5194/acp-2021-1067 Preprint. Discussion started: 6 January 2022 c Author(s) 2022. CC BY 4.0 License. aldehyde based on previous studies (Li et al., 2011). This indicates that the low oxidized monomeric compounds (O<5), which are abundant at lower temperatures, can also be formed at higher temperatures (273-313K) but react (cf. Fig. S7) to form higher oxygenated and lower volatile compounds. It cannot be excluded that low molecularweight compounds, like C4H6O4 and C2H4O3, might be from the similar process. 310 Figure 6 shows the particle-phase mass spectra from BCP ozonolysis for 213 K and 313 K. For both lowest and highest temperatures, several first-and second-generation oxidation products, some of which have been identified also in previous studies, were observed, e.g. C14H22O4 (β-caryophyllinic acid or β-hydroxynocaryophyllon aldehyde), C15H24O3 (β-hydroxycaryophyllon aldehyde or β-caryophyllonic acid), and C14H22O7 (2,3-dihydroxy-315 4-[2-(4-hydroxy-3-oxobutyl)-3,3-dimethylcyclobutyl]-4-oxobutanoic acid) (Jaoui et al., 2007;Li et al., 2011;Winterhalter et al., 2009;Chan et al., 2011;Jaoui et al., 2003;Griffin et al., 1999;Lee et al., 2006a;Lee et al., 2006b;Jenkin et al., 2012;. Table S3 lists all major particulate CxHyOz compounds detected by FIGAERO-iodide-CIMS in this work. Furthermore, we also observed e.g., C14H20O2 H + , C14H20O3 H + , C14H22O3 H + , C15H22O2 H + and C15H22O3 H + with the CHARON-PTR-MS (Fig. S6). From previous 320 studies we know that CHARON-PTR-MS measurements are affected by fragmentation, e.g. by losing H2O, CO and CO2, due to the relatively high collisional energy in the drift tube (100-170 Td) (Gkatzelis et al., 2018). In this study, we operated the CHARON-PTR-MS at 100 Td for the particle measurement. Taking fragmentation by losing one H2O into account, it is reasonable to speculate that C14H20O3 and C15H22O2 are from the fragmentation of C14H22O4 and C15H24O3, respectively. Similarly, C14H20O2 and C15H22O3 in CHARON-PTR-MS mass spectra 325 could be identified as the fragmentation ions from C14H22O3 and C15H24O4, respectively, which were the most abundant ions in the FIGAERO-iodide-CIMS mass spectra as shown in Fig. 6.

Composition of the particle-phase products
At 213 K, monomers, dimers and trimers are clearly visible. The most abundant compounds measurable with our FIGAERO-iodide-CIMS in each group are C15H24O3, C30H48O5 and C44H68O9, respectively. At 313 K, the monomers dominate and only a few dimers are observed, with the most abundant signals by compounds C14H22O7 330 and C29H44O10, respectively.
Compared to 213K, it is evident that the monomeric compounds formed at 313K are more oxygenated and have higher elemental O:C ratios (Fig. 6). It is inferred that at higher temperatures, once the first-generation products are formed in the gas phase, some of them can remain in the gas due to higher saturation vapor pressures. and undergo further oxidation reactions of their unsaturated exocyclic double bonds with the excess of ozone. Since 335 the saturation vapor pressures of the compounds at 213K are substantially lower than at 313K, more relatively lower oxidized molecules are found in the particle phase due to rapid condensation. For the compounds remaining in the gas phase, HOMs such as e.g. C14H22O7 could be formed via simple or extended autoxidation (Richters et al. (2016)). In addition to C14H22O7, we also detected several other compounds (e.g. C14H22O9, C15H22O7,9, and C15H24O7,9) that are likely products of autoxidation reactions (Jokinen et al., 2016). At 313K, the monomeric 340 highly oxidized compounds (MHOC, C≤15, O≥6) dominate the monomers with a signal fraction of 42.5% to total organic signals, which exceeds the contribution of other monomeric low oxygenated organic compounds (MLOC, C≤15, O<6) with a signal fraction of 24.9%. For comparison, at 213K, MHOC and MLOC contribute 6.9% and 30.5%, respectively. Furthermore, the six confirmed HOM have signal fractions of 9.2% at 313K and nearly zero at 213K. Note that higher oxygenated autoxidation products like C15H22O11 (detected by Atmospheric Pressure interface Time-Of-Flight mass spectrometer (CI-APi-TOF) using nitrate as the reagent ion (Jokinen et al., 2016)) and C15H22O13 could not be detected in this work due to instrument limitations (Riva et al., 2019). To summarize, the relative abundance of HOMs were higher at increasing temperatures (Fig. 8), indicating that the autoxidation showed a strong temperature dependence, slowing down at reduced temperatures.
The dimer groups show two completely different patterns at 213K and 313K. At 213K, the dimers mainly consist 350 of low oxygenated organic compounds (DLOC) with 28-30 carbon atoms and 5-8 oxygen atoms, and the total signal fraction of the dimeric compounds is 53.7%. At 313K, dimers are more oxygenated with 9-11 oxygen atoms with the same carbon number of 28-30 (DHOC), and they contribute less to the total normalised organic signal (27.6%). Here, we put forward esterification as a potential pathway for forming the most abundant dimers at both 213K and 313K, similar to the dimer formation of other biogenic VOCs suggested by Yasmeen et al. (2010) and 355 Müller et al. (2008). The dominating dimeric molecule at 213K, C30H48O5, could potentially be formed via esterification of two of the most abundant monomers (C15H26O3 and C15H24O3). In a similar way, the dimer C29H44O9 could be formed at 313K from C14H22O7 and C15H24O3. These reactions are described in Fig. S8 in the supplement.
However, we cannot exclude the reaction of a BCP-derived stabilized Criegee intermediate and an abundant acid 360 as a potential pathway for C30H48O5 formation, similar to mechanisms suggested for e.g. α-pinene (Kristensen et al., 2016;Wang et al., 2016;Witkowski and Gierczak, 2014;Lee and Kamens, 2005). The dimers we observed had no more than 11 oxygen atoms, which is due to low sensitivities of FIGAERO-iodide-CIMS to these compounds (Riva et al., 2019).
Significant signals of trimers at 213K are assigned to C41-43H62-68O9-11, but they are not detected at 313K. The 365 potential formation pathway of C44H68O9 at 213K is also included in Fig. S8. Please note, that the assignment for ions at mass to charge ratios of more than 700 Th has significantly higher uncertainties as for smaller mass peaks. ). This indicates again that at higher temperatures, after ozonolysis of the endocyclic bond (formation of first-generation oxidation products), the unsaturated compounds can react further with the excess of ozone and form higher oxidized products (e.g. HOM), while those formed at lower temperatures would partition into the condensed phase before further oxidation can occur. As shown in Fig. 8, the monomer groups (MHOC+MLOC) 375 contribute 39.2%, 64.7%, 85.3%, 68.9% and 67.5% to the total signal from 213K to 313K, respectively. Among all the monomers, the signal fraction of the six identified HOM to the total signals of all organic species has a monotonic positive temperature dependence (cf. Fig. 8), increasing from 0.1% to 9.2% for temperatures increasing from 213K to 313K. This is a similar correlation between HOM formation and temperatures as observed by (Bianchi et al., 2019). 380 Two different dimeric patterns appear in the temperature range of 213-313K. One pattern is represented by molecular formulae of C28-30H42-48O5-8 at 213-243K (marked as low temperature group, LT-group), and the other pattern is represented by C28-30H36-44O9-11 at 273-313K (marked as high temperature group, HT-group). The LTgroup contributes 53.7% at 213K and 32.8% at 243K, with a negative temperature dependence, while the dimeric signal fraction of the HT-group is lower than LT-group, contributing 13.8% at 273K, 24.6% at 298K, and 27.6% at 313K, respectively, as shown in Fig. 8. After 273K, dimer formation is enhanced with increasing temperatures.
The contribution in gas and particle phase of the major compounds are shown in Fig. S9.

Chemical characterization of SOA from BCP ozonolysis in presence of nitrogen oxides
In this section we discuss the chemical composition of SOA from BCP ozonolysis in the presence of nitrogen oxides including NO3 radicals, which refers to the SOA formed after the last addition of BCP, e.g. 180-190 min 390 in Fig. 2. Please note that the results given here refer to the total SOA which was formed in two steps, first by pure ozonolysis and in a subsequent step including nitrogen oxides. The SOA mass formed in the presence of nitrogen oxides compared to the total SOA mass detected corresponds to 49% at 213K, 34% at 243K, 49% at 273K, 65% at 298K, and 63 % at 313K. Due to the excess of ozone besides NO2, also NO3 radicals and N2O5 were present. Thus, the BCP was now also oxidized by reaction with NO3 radicals, with a major pathway to 395 produce organonitrates (org-Ns) (Kiendler-Scharr et al., 2016;Wu et al., 2021). The concentrations of NO3 radicals before the final addition of BCP were estimated for each experiment using a kinetic box model (details in Fig. S10) and the results are given in Table 1.
Based on the ozone and NO3 concentration levels as well as the corresponding reaction rates, we estimated the fraction of NO3 radicals contributing to the initial BCP oxidation to 84%, 90% and 72% for 273, 298 and 313K. 400 Figure 9 shows the averaged gas-phase mass spectra including molecules without nitrogen atom (org) and organonitrates (org-Ns) for all temperatures as detected by CIMS after the particle concentration got stable after the last BCP addition (e.g., at 298K, referring to the time period after 160 min in Fig. 2). The gas phase organonitrates showed an abundance increasing with temperature from 20.7% at 213K, 26.0% at 243K, 38.3% at 405 273K, 46.5% at 298K, to 48.9% at 313K. These compounds consisted of three groups of different carbon numbers (C5H7O6N, C10H15O5-7N and C15H23,25O6-8N). To illustrate more clearly the organonitrate formation, we show the time evolution of the three most abundant org-Ns in these three groups in the right panel of Fig. 9. The signals of C5H7O6N and C10H15O6N increased after the NO2 addition immediately, indicating that their formation was related to reactions between BCP oxidation products (BCP+O3) and NO3 radicals. After the start of the last BCP addition, 410 C15H25O7N started to increase significantly, indicating that its formation was linked to the reaction of BCP and NO3 directly, but not the reaction between the nitrate radicals and oxidation products from BCP ozonolysis. Figure 10 shows the particle chemical composition of SOA from BCP ozonolysis in the presence of NO2 at 213 K (upper panel) and 313 K (lower panel). At 213K (upper panel), org dominated the particle composition, with a 415 signal fraction of 97.1% to total signals (org-Ns + org), similar to the SOA before NO2 addition at 213K. Org groups of monomers (41.2% in signal fraction), dimers (48.2%) and trimers (7.4%) were observed. The most abundant signals in each group were C15H24O3, C30H48O5 and C44H68O9, respectively. The largest org-Ns signal was from C15H25O7N, contributing 0.6% to the total signals. It is obvious that only few org-Ns were formed at 213K in our study, with a contribution ([org-Ns]/[total org.]) of 2.8% measured by FIGAERO-iodide-CIMS 420 (normalised signal fraction, Fig. 12) and 0.08 detected by HR-AMS (Fig. S11).
The particle mass spectra for all temperatures are shown in Fig. 11, with relative signal abundance of individual molecule to total detected species, including pure organic components (org, red) and organonitrates (org-Ns, blue).
Among all the org, the most abundant signal at 298-313K was not C14H22O7 as for pure ozonolysis, but C15H24O4 430 (NO3 present), due to the additional formation of pure MLOCs. This could be confirmed by comparison of the absolute signals of C14H22O7 and C15H24O4 in the particles before and after the last BCP addition (Fig. S12).
Moreover, the dimeric compounds with 20 carbon atom skeletons (i.e. C20H24O7-8, insertion in Fig. 10) and the trimeric compounds with 35 carbon atom skeletons (i.e. C35H48O12, Fig. 10 and Fig. 11) were newly formed at higher temperatures (> 273K) in the presence of nitrogen oxides. However, it cannot be excluded that they could 435 be formed by reaction of the oxidation products from BCP ozonolysis (nitrogen oxides absent) and the next step (nitrogen oxides present). In contrast, the mass spectra of non-N-containing organic species (org) at 213-243K showed no substantial changes compared to the species from ozonolysis without nitrogen oxides present (cf. Fig.   7). One obvious reason for this is the lower NO3 radical concentration at lower temperatures but also changes in the active reaction pathways may play a role. 440 In addition, more organonitrates were detected at increased temperatures, ranging from 2.8% (213K) to 51.5% (298K) and 48.9% (313K), dominated by monomeric org-Ns (C15H23,25O6-10N), wherein the most abundant signals were from C15H25O7N at 243-273K and C15H23O9N at 298-313K. Monomeric organonitrates contributed 1.7% to 40.1% from 213 K to 298K, and 35.5% at 313K to total organic signals, as shown in Fig. 12. Besides, the signalweighted averaged O:C of organonitrates monotonically increased from 0.41 to 0.51 from 213K to 298K, and 445 0.50 at 313K. We assume that the positive impact of temperature on the oxygenation and formation of organonitrates could also be relevant for the highest temperature (313K). However, the higher oxidized organonitrates may be out of the detection range of the FIGAERO-iodide-CIMS, resulting in less signal fractions and lower signal-weighted averaged O:C ratios of organonitrates at 313K. This is supported by HR-TOF-AMS measurements (Fig. S11), which show increasing organonitrate fractions from 8% to 61% also for 313 K. On the 450 other hand, a potential thermal instability of some organonitrates may also be an explanation for the weaker increase of their fraction observed for 313K.
It should be noted that the nitrate radical levels were estimated to be higher at higher temperatures (Table 1), which partially explains the increasing organonitrates formation at higher temperatures. The orgnonitrates detected in this study were dominantly with the same carbon atom skeleton (C15) and only one organonitrate 455 functional group (-ONO2). The O:C ratios for organonitrates increase with temperature. Thus, it can be concluded that higher temperatures favour the formation of higher oxygenated organonitrates from the BCP ozonolysis in the presence of NO3 radicals. The contribution in gas and particle phase of the major compounds are shown in Fig.   S13.

Summary and conclusions 460
In this work, a series of experiments conducted in the dark AIDA chamber with temperatures covering the whole tropospheric range (213-313K) were analysed to investigate the yields, kinetics and chemistry of BCP ozonolysis in the absence and presence of nitrogen oxides. The rate coefficient of the endocyclic double bond in BCP reacting with ozone was determined in the temperature range between 243 and 313K showing decreasing values with increasing temperature. The rate coefficients agree well with literature data at 296 K and with quantum chemical 465 calculations of the temperature dependence. We determined a reaction enthalpy of (5.6±1.0) KJ mol -1 and OH radical yields increasing from (5±2) % at 243K to (15±2) % at 313K. SOA yields determined for the ozonolysis of BCP show about 50% smaller values than literature data at 298 K, which is still within the combined uncertainty limits. For the first time the temperature dependence of the SOA yield was determined showing values decreasing from (37±11) % to (16±5) % for temperatures increasing from 470 243 to 313K and a constant organic particle mass of 10 µg m -3 . This allows to calculate the potential of BCP to contribute to SOA formation e.g. if reaching higher altitudes in the atmosphere.
The chemical characteristics of BCP pure organic species and organonitrates were determined by the FIGAERO-CIMS using Ias the reagent ion. Major products and different chemical composition of gas and particle phase with and without NO3 present at all temperatures were resolved. The variation of the ozonolysis temperature 475 revealed substantial impact on the abundance of individual pure organic molecules without nitrogen atoms (org) and organonitrate molecules (org-Ns). In the first generated SOA without nitrogen oxides present, monomers (mainly C14-15H22-24O3-7) and dimers (mainly C28-30H44-48O5-9) were abundant, wherein minor signals of trimers (mainly C41-44H62-66O9-11) were mainly detected at 213K. Potential dimer and trimer formation pathways are proposed. With temperature increasing to 313K, monomers and dimers (C14-15H22-24O6-9 and C27-29H42-44O9-11, 480 respectively) became more oxidized, and no significant trimeric signals were detected.
The positive temperature dependence of the oxygenation of the products was also observed in the BCP organonitrates. In the presence of nitrogen oxides, most of the organonitrates were found as monomers with a C15 skeleton with one nitrate group, with their signal-weighted O:C ratio increasing from 0.41 to 0.51 for temperatures in the range between 213K and 313K. Dimeric and trimeric pure organic species without nitrogen atoms (C20, C35) 485 were newly formed in the presence of nitrogen oxides at 298-313K, which substantially changed the chemical composition of pure organic components and indicates more termination ways might exist.
This work helps to get a better understanding on the yields, kinetics and chemical composition of SOA from BCP ozonolysis over a relatively wide range of temperatures, 213 K to 313 K, which is representative of the real atmosphere from boundary layer to upper troposphere. In addition, SOA volatility is expected to have a strong 490 impact on the SOA formation, and will be discussed in our upcoming paper focusing on the desorption of BCP SOA from filters but also the warming up of the aerosol in the simulation chamber overnight.