Investigation of atmospheric VOCs sources and ozone formation sensitivity during epidemic closure and control: A case study of Zhengzhou

Abstract

This study investigates the pollution characteristics of volatile organic compounds (VOCs) and their impact on ozone formation in the urban area of Zhengzhou. The analysis is based on the air quality data collected during the epidemic control period (P3) from July 20 to August 22, 2021, as well as the same period in 2019 and 2020 (P1 and P2). The results reveal a decreasing trend in the O3 precursors, namely NO2 and VOCs, from 2019 to 2021. During the P3 period, the mean concentrations of NO2 and VOCs were 19 μg/m3 and 56 μg/m3, respectively, a decline of 32% and 36% compared to the levels in P2. However, the mean MDA8 concentration in P3 was 142 μg/m3, 25% higher than that in P2, and ozone-polluted days was 12 d, 6 days more than that in P2. The VOCs composition profiles were similar across three periods, with alkanes accounting for 34%, 36%, and 39% of TVOC, respectively. Six kinds of VOCs sources were quantified by positive matrix factorization (PMF), among which vehicle emissions contributed the most (29%), followed by solvent usage (23%) and industrial processes (22%). The contribution of industrial processes and vehicle emissions declined significantly in P3, while that of stationary combustion and LPG/NG sources increased. The net production rate P(Ox) increased in P3 compared to that in P2, getting closer to the ridge line, indicating that O3 formation was gradually transiting from VOCs control zone to synergistic control zone. Therefore, VOCs and NOx emissions should be reduced synchronously.