Upward trend and formation of surface ozone in the Guanzhong Basin, Northwest China

Abstract

Increase trend of surface ozone (O3) was observed in the Guanzhong Basin (GZB) from 2014 to 2020 with growth rates of 3.9–6.4 μg m−3 yr−1 for the maximum daily average 8 h (MDA8) O3 concentrations. To further understand the formation of O3, investigation of volatile organic compounds (VOCs) was carried out in the summer of 2018. High levels of VOCs were observed in both residential area and industrialized cities. Elevated concentrations of none-methane Hydrocarbon (NMHCs) were observed in rush hours, which indicated dominated roles of traffic activities on the loading of ambient VOCs. In the nighttime, both of NMHCs and oxygenated VOCs (OVOCs) were raised, and the peaks of VOCs kept pace with accumulation of O3. Wind field indicated that northward and westward air mass, which passed through the remote forest and industrial area in east of the GZB, was responsible to elevated ambient VOCs in the GZB. Traffic emission, fuel evaporation, and solvent using were key contributors to ambient NMHCs, while solvent using and secondary formation dominated the loading of OVOCs. The present study indicated that both local management and regional collaborative control on active VOCs species from typical sources is urgently needed in GZB.