Seasonal variability and source apportionment of non-methane VOCs using PTR-TOF-MS measurements in Delhi, India

Abstract

Volatile organic compounds (VOCs) are ubiquitous atmospheric constituents and play important roles in tropospheric photochemistry. The real-time chemical characterization of VOCs was carried out in this study using the proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) at an urban site of Delhi for the complete year of 2019. The average concentrations of total VOCs ranging from m/z 31.02 to 181.12 were 131.3 ± 96, 78.7 ± 47.3, 151.2 ± 83.2, 199.6 ± 101.2 ppbv in the winter, summer, monsoon, and post-monsoon seasons, respectively. The positive matrix factorization (PMF) receptor model on an advanced ME-2 engine was used to perform source apportionment analysis. This analysis reveals two traffic-related factors, two solid-fuel combustion factors, two secondary VOC factors, one biogenic, and one solvent-use factor depending upon the season. The traffic-related emissions mainly comprised of aromatics and simple non-aromatics, contributed about 31% (∼one-third) of the total VOCs measured over the study period. Solid fuel combustion factors consisting of phenols, furans, and nitrogen-containing compounds contributed about 28%, while Secondary VOCs contributed about 31% cumulatively over the study period. The contributions of biogenic sources were significant only during the summer and monsoon seasons. A local source near the sampling site was identified as a solvent-use factor, mainly comprised of ethyl acetate due to the renovation work near the sampling site during monsoon and post-monsoon season. The difference in the profile of primary sources was influenced by the local emissions and regional transport of air masses. Meteorological conditions and planetary boundary layer highly influence the formation of secondary VOCs.