Abstract
Restrictions on human activities remarkably reduced emissions of air pollutants in China during the COVID-19 lockdown periods. However, distinct responses of O3 concentrations were observed across China. In the Beijing–Tianjin–Hebei (BTH) and Yangtze River Delta (YRD) regions, O3 concentrations were enhanced by 90.21 and 71.79% from pre-lockdown to lockdown periods in 2020, significantly greater than the equivalent concentrations for the same periods over 2015–2019 (69.99 and 43.62%, p < 0.001). In contrast, a decline was detected (−1.1%) in the Pearl River Delta (PRD) region. To better understand the underlying causes for these inconsistent responses across China, we adopted the least absolute shrinkage and selection operator (Lasso) and ordinary linear squares (OLS) methods in this study. Statistical analysis indicated that a sharp decline in nitrogen dioxide (NO2) was the major driver of enhanced O3 in the BTH region as it is a NOx-saturated region. In the YRD region, season-shift induced changes in the temperature/shortwave radiative flux, while lockdown induced declines in NO2, attributable to the rise in O3. In the PRD region, the slight drop in O3 is attributed to the decreased intensity of radiation. The distinct regimes of the O3 response to the COVID-19 lockdown in China offer important insights into different O3 control strategies across China.
Highlights
Tropospheric O3 is formed through complex reactions involving volatile organic compounds (VOCs) and nitrogen oxides (NOx), along with influences of meteorological conditions
O3 concentrations usually exhibit a nonlinear response to source emissions of precursors, in such a way that the O3 response to emission control of one precursor (e.g., NOx ) depends on emissions of other precursors (e.g., VOCs) due to their complex interactions [1]
We considered near surface temperature (T2), wind speeds (WS10), relative humidity (RH2), and mean surface net shortwave radiation flux (SWR) in this study
Summary
Tropospheric O3 is formed through complex reactions involving volatile organic compounds (VOCs) and nitrogen oxides (NOx), along with influences of meteorological conditions There have been considerable attempts made to examine relationships between O3 and influencing factors, such as VOCs, NO2 , sunshine hours, temperature, wind speed, relative humidity, daily precipitation amount, surface pressure and geopotential height [1,2,3,4,5,6]. It was demonstrated that the O3 sensitivity regimes and leading influencing meteorological factors vary across regions and time periods [1,2,3,4,5,6].
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