Spatiotemporal variation, sources, and secondary transformation potential of volatile organic compounds in Xi'an, China

Mengdi Song,Limin Zeng,Xuena Yu,Ningning Zhang,Xin Li,Keren Liao,Suding Yang,Qi Chen,Yuanhang Zhang,Shiyi Chen,Keding Lu,Yiming Yang,Junji Cao,Huabin Dong,Songxiu Zhou

doi:10.5194/acp-21-4939-2021

Abstract

Abstract. As critical precursors of ozone (O3) and secondary organic aerosols, volatile organic compounds (VOCs) play a vital role in air quality, human health, and climate change. In this study, a campaign of comprehensive field observations and VOC grid sampling was conducted in Xi'an, China, from 20 June to 20 July 2019 to identify the spatiotemporal concentration levels, sources, and secondary transformation potential of VOCs. During the observation period, the average VOC concentrations at the Chanba (CB), Di Huan Suo (DHS), Qinling (QL), and gridded sampling sites were 27.8 ± 8.9, 33.8 ± 10.5, 15.5 ± 5.8, and 29.1 ± 8.4 ppb, respectively. Vehicle exhaust was the primary source of VOC emissions in Xi'an, and the contributions of vehicle exhaust to VOCs at the CB, DHS, and QL sites were 41.3 %, 30.6 %, and 23.6 %–41.4 %, respectively. While industrial emissions were the second-largest source of VOCs in urban areas, contributions from aging sources were high in rural areas. High potential source contribution function values primarily appeared in eastern and southern Xi'an near the sampling site, which indicates that Xi'an exhibits a strong local VOC source. Moreover, alkenes, aromatics, and oxygenated VOCs played a dominant role in secondary transformation, which is a major concern in reducing O3 pollution in Xi'an.

Highlights

Atmospheric pollution in China is characterized by frequent secondary pollution, which is primarily reflected by the yearly increasing ozone (O3) concentrations and proportion of secondary organic aerosol (SOA) components in PM2.5 (Lu et al, 2018; Huang et al, 2014)
Based on an in-person investigation, the prevailing winds, and the electricity supply, three sites were chosen for the field observation campaign (Fig. 1): the Chanba (CB; 34◦20 12 N, 109◦01 35 E), Di Huan Suo (DHS; 34◦13 49 N, 108◦52 58 E), and Qinling (QL; 34◦04 11 N, 108◦20 31 E) sites, which were located on upwind, downtown, and downwind areas of Xi’an city, respectively
Higher temperatures may accelerate a secondary transformation of Volatile organic compounds (VOCs) into O3, resulting in more frequent O3 pollution incidents in Xi’an; the mean O3 concentrations at the CB, DHS, and QL sites reached 50.2 ± 29.9, 47.6 ± 29.4, and 19.7 ± 8.0 ppb, respectively

Summary

Introduction

Atmospheric pollution in China is characterized by frequent secondary pollution, which is primarily reflected by the yearly increasing ozone (O3) concentrations and proportion of secondary organic aerosol (SOA) components in PM2.5 (Lu et al, 2018; Huang et al, 2014). Volatile organic compounds (VOCs) are vital precursors of O3 and SOA, and reducing VOC emissions is crucial for controlling O3 and PM2.5 pollution (Jin and Holloway, 2015; Yuan et al, 2013). VOC sources can be divided into biogenic and anthropogenic sources. Anthropogenic VOC sources primarily include vehicle exhaust, industrial, paint solvent usage, combustion, and fuel evaporation sources. The source apportionment of observation results found that the contribution of vehicle exhaust sources to VOCs plays a leading role in VOC emissions in China, reaching 22 %–58 % (Jia et al, 2016; Liu et al, 2016a, 2020; Zhang et al, 2019). Paint solvent usage is the main source of VOCs in Langfang and Xiamen city

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Conclusion