Source identification of VOCs at an urban site of western India: Effect of marathon events and anthropogenic emissions

Abstract

AbstractAmbient volatile organic compounds (VOCs) were measured using a high‐resolution proton transfer reaction‐time of flight‐mass spectrometer at an urban site of Ahmedabad in India during the winter season in 2014. Mixing ratios of VOCs show large diurnal and day‐to‐day variations. Although strongly influenced by local emissions, periods of higher VOCs were observed during transport from the polluted Indo‐Gangetic Plains than those from the cleaner Thar Desert. However with different rates, VOCs decreased exponentially with increasing wind speed. Relative abundance of methanol varied with weather conditions contributing highest and lowest under fog and clear‐sky conditions, respectively. Among the compounds reported here, oxygenated VOCs (OVOCs) contribute to a large fraction (67–85%) with methanol being most abundant (40–58%). In spite of predominant vehicular emissions, diurnal distribution and emission ratios (ERs) of several VOCs indicate the role of biogenic and secondary sources. The ratios of isoprene/benzene and OVOCs/benzene show significant enhancements during daytime suggesting their contributions from biogenic and secondary sources. During marathon and cyclothon events, mixing ratios of VOCs were 2–10 times higher compared to a normal Sunday. The ERs of VOCs estimated using the nighttime data on marathon day are well within the range of values reported for several megacities of the world. The average contributions of primary anthropogenic sources to acetaldehyde, acetone, and isoprene were 44 ± 06%, 45 ± 07%, and 63 ± 12%, respectively. During cloudy condition, the increase in anthropogenic contribution to acetaldehyde (~10%), acetone (9%) and isoprene (30%) is due to reduction in biogenic emissions and secondary formation of these VOCs.