Characteristics of summertime ambient VOCs and their contributions to O3 and SOA formation in a suburban area of Nanjing, China

Abstract

Hourly concentrations of 89 volatile organic compounds (VOCs) together with other atmospheric trace gases like ozone (O3), oxides of nitrogen (NOx), carbon monoxide (CO), and sulfur dioxide (SO2) were measured continuously in a suburban area of Nanjing, China. The investigations were conducted during the summer, 2018 to better characterize airborne VOC and their influence on O3 and secondary organic aerosols (SOA) formation. The average hourly total VOCs (TVOCs) concentration was 35 ± 21 ppbv which was mainly contributed by different alkanes (41%) followed by halohydrocarbons and oxygenated volatile organic compounds (31%), aromatics (16%), alkenes (9%), and alkyne (3%). The TVOCs concentration was in a similar range with the ones observed in other urban and suburban areas in China. Traffic had an important influence on the air quality in the study area as the diurnal variation of the trace gases depicted a bimodal distribution that coincides with the rush-hours. The O3 concentrations exceeded both the national and international air quality standards. The VOC:NOx was much higher than 8:1, indicating ambient air was NOx limited to atmospheric O3 formation, therefore, reduction of NOx concentration could reduce O3 formation rates more effectively. The average hourly ozone formation potential (OFP) of the VOCs was 218 μg m−3 and the major contributors to it were aromatics (43%) and alkenes (23%). The average hourly secondary organic aerosol formation potential (SOAFP) of the VOCs was 0.9 μg m−3. Similar to the OFP, aromatic VOCs were the major contributors to the total SOAFP. To improve the air quality in the study area traffic emissions as well as the aromatic and alkene VOCs emissions reduction are necessary.