Characteristics of VOCs and their contribution to O3 and SOA formation across seasons over a metropolitan region in India

Abstract

Understanding and quantifying the influence of volatile organic compounds (VOCs) on ozone and secondary organic aerosol formation is essential for better prediction/estimation of these products. A total of 9 VOCs along with surface ozone were measured during the year 2019 at Pune (India) location. The ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) estimations are compared for 2 methods-using measured VOC concentrations and using their photochemical initial concentrations (PIC). The OFP and SOAFP estimated based on the measured VOC concentrations provide an incomplete understanding of these 2 formation processes. This is mainly because measured VOCs don't account for the photochemical losses that compounds undergo from the source to the receptor. The PIC values of VOCs have been estimated in this study to highlight the importance of considering the photochemical losses. For example, the PIC value of highly reactive compound, isoprene, was found to be 152% higher (1.48 ppbv) than its measured value (0.59 ppbv). The resultant total OFP estimate based on PIC values of all the VOCs was found to be 53.30 ± 35.02 ppbv as compared to 45.99 ± 29.35 ppbv obtained from measured VOCs. Based on k-means clustering analysis, it was found that the highest ozone formation was favored under transition regime chemistry when PIC values were considered. The average total SOAFP based on PIC values was found to be 1.32 ± 1.40 ppbv, while it was 1.17 ± 1.18 ppbv for measured VOCs. The aromatics contributed to over 90% of total SOAFP estimated for the region.