Sources-oriented contributions to ozone and secondary organic aerosol formation potential based on initial VOCs in an urban area of Eastern Asia

Abstract

Over the past decades, the pollution of ozone (O3) and secondary organic aerosols (SOA) in the atmosphere has become a major concern worldwide due to their adverse effects on human health, air quality and climate. Volatile organic compounds (VOCs) are crucial precursors of O3 and SOA, but identifying the primary sources of VOCs that contribute to the formation of O3 and SOA has been challenging due to the rapid consumption of VOCs by oxidants in the air. To address this issue, a study was conducted in a Taipei urban area in Taiwan, where the hourly data of 54 VOC species were collected from March 2020 to February 2021 detected by Photochemical Assessment Monitoring Stations (PAMS). The initial mixing ratios of VOCs (VOCsini) were determined by combining the observed VOCs (VOCsobs) and the consumed VOCs resulting from photochemical reactions. Additionally, the ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) were estimated based on VOCsini. The OFP derived from VOCsini (OFPini) was found to exhibit a strong correlation with O3 mixing ratios (R2 = 0.82), whereas the OFP obtained from VOCsobs did not show such a correlation. Isoprene, toluene and m,p-xylene were the top three species contributing to OFPini, while toluene and m,p-xylene were the top two contributors to SOAFPini. Positive matrix factorization analysis revealed that biogenic, consumer/household products, and industrial solvents were the major contributors to OFPini in four seasons, and SOAFPini mostly came from consumer/household products and industrial solvents. This study highlights the importance of considering photochemical loss caused by different VOCs reactivity in the atmosphere when evaluating OFP and SOAFP. Moreover, it emphasizes the need to prioritize controlling the sources emitting the dominant VOC precursors of O3 and SOA to effectively alleviate the scenarios of elevated O3 and particulate matter.