The influence of UV-light irradiation and stable Criegee intermediate scavengers on secondary organic aerosol formation from isoprene ozonolysis

Abstract The formation of secondary organic aerosol (SOA) from isoprene ozonolysis was investigated using a FEP Teflon reactor with and without the presence of H 2 O, CO, SO 2 and UV-light irradiation (365 nm) to reveal their possible influence on SOA formation. Compared with the base experiment (isoprene + O 3 ) under dark condition, the presence of 2000 ppm H 2 O and 1000 ppm CO could remarkably suppress SOA formation from isoprene ozonolysis, with SOA yields reduced from 2.96% to 1.47% and 2.08%, respectively. The evident reduction of SOA yields from isoprene ozonolysis with the presence of H 2 O and CO was mainly ascribed to the suppression of Stable Criegee Intermediates (SCIs). In contrast, the particle yield from isoprene ozonolysis with the presence of SO 2 pronouncedly increased from 2.96% to 57.9%, suggesting that the oxidation of SO 2 by SCIs made great contribution to the particle formation. The SOA or particle yields from all the reaction systems with and without presence of H 2 O, CO and SO 2 reduced more than 27% under the UV-light irradiation with respect to dark condition, which were mainly attributed to the SCIs photolysis. The contribution of OH channel to SOA formation from isoprene ozonolysis was estimated to be less than 30%. Considering the 50% reduction of SOA yield from isoprene ozonolysis under light irradiation, the disappearance of the component with low O:C and H:C and high molecule weight in the SOA sample collected under light irradiation indicated the polymerization of unsaturated SCIs might be an important SOA formation channel besides the oligomerization of SCIs, HCHO, and MACR from isoprene ozonolysis under dark condition.