Real-time characterization of isoprene epoxydiols-derived secondary organic aerosol (IEPOX-SOA) in Eastern China

Abstract : Isoprene (2-methyl-1,3-butadiene, C5H8), from biogenic emissions, is a significant source of global non-methane hydrocarbon in the atmosphere. Its oxidation products (isoprene epoxydiols, IEPOX) can form secondary organic aerosol (SOA) and exert potential impacts on air quality and regional climate. Although a few studies have reported the isoprene-related organic aerosol in China's atmosphere via filter-based measurements, real-time characterization of IEPOX-derived SOA (IEPOX-SOA) has never been performed to date. Here we report the identification and quantification of IEPOXSOA based on Aerosol Chemical Speciation Monitor (ACSM) measurements in Eastern China in summer 2013 along with multilinear engine (ME-2) analysis of OA spectra. The average mass concentration of IEPOX-SOA is 0.33±0.19μg/m3 for the entire study period, which accounts for 3.8% of total OA. IEPOX-SOA presents a strong diurnal cycle with a clear daytime increase related to photochemical production. The IEPOX-SOA correlated well with sulfate (r = 0.61), suggesting that anthropogenic SO2 emissions might affect the IEPOXSOA formation in urban Nanjing. Potential source contribution function analysis shows that high IEPOX-SOA is primarily from the south of Nanjing with substantially large biogenic emissions. Our results suggest that the interactions between anthropogenic SO2 and biogenic VOCs from regional transport might have played a key role in the formation of IEPOX-SOA in Eastern China.