Secondary organic aerosol formation from photooxidation of a mixture of dimethyl sulfide and isoprene

摘要

Secondary organic aerosol (SOA) created from the photooxidation of a mixture of isoprene and dimethyl sulfide (DMS) was studied at different NO_x concentrations (40-220 ppb) and humidities (12%, 42% and 80%) using a Teflon film indoor chamber. To study the effect of isoprene on DMS products, the major DMS photooxidation products, such as sulfuric acid, methanesulfonic acid (MSA) and methanesulfinic acid (MSIA), were quantified in both the presence and the absence of isoprene using a Partide-Into-LiquidSampler coupled with Ion Chromatography (PILS-IC). The resulting PILS-IC data showed that the DMS aerosol yield significantly decreased due to the photooxidation of isoprene. A 35.2% DMS aerosol yield reduction was observed due to 800 ppb isoprene in 185 ppb NO_X and 140 ppb DMS. Among the aerosolphase DMS oxidation products, MSA was the most sensitive to the presence of isoprene (e.g., 46% reduction). The DMS aerosol product analysis indicates that isoprene oxidation affects the pathways of MSA formation on the aerosol surface. Using a new approach that implements an Organic Carbon (OC) analyzer, the isoprene SOA yield (y_(iso)) in the DMS/isoprene/NO_x system was also estimated. The OC data showed that Y_(iso) increased significantly with DMS compared to the V_(iso) without DMS. For example, Y_iso with 80 ppb NO_x and 840 ppb isoprene was increased by 124.6% due to 100 ppb DMS at RH = 42%. Our study suggests that the heterogeneous reactions of isoprene oxidation products with the highly acidic products (e.g., MSA and sulfuric acid) from DMS photooxidation can considerably contribute to the Y_(iso) increase.