Reply on RC2

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.