Simultaneous observations of peroxyacetyl nitrate and ozone in Central China during static management of COVID-19: Regional transport and thermal decomposition

Abstract

Peroxyacetyl nitrate (PAN) and ozone (O3) are two typical indicators of photochemical pollution, which are harmful to human body and environment. In this study, PAN and O3 were continuously monitored during static management (SM) of the COVID-19 epidemic in Zhengzhou. Briefly, SM refers to control policies in that all except for essential business are closed; work at home; and no people going out and no gathering, etc. During the SM, the temperature suddenly dropped from 26 °C to 14 °C, which provided a good experimental condition for the study of source transformation, accumulation, and consumption of PAN in the atmosphere. The concentrations of PAN were 0.6, 0.8, and 0.5 ppbv in three periods: before, during, and after the SM. During the SM, the lifetime of PAN was increased due to low temperature, and the accumulation time of PAN was longer, resulting in the increase of PAN concentration in daytime faster than the other two periods. During SM, especially after the temperature drops, the average atmospheric lifetime of PAN was 23.8 h, which was higher than 17.6 h before SM and 13.8 h after SM. This indicated that low temperature was more conducive to the accumulation of PAN. The high potential PAN source (CBPF>0.8) mainly came from the northeast of Zhengzhou, and the wind speed range was between 2.5 and 3 m/s. The backward trajectory analysis showed that 83.3% of the air mass from the northeast and northwest had a greater impact on the PAN concentration in Zhengzhou.