Insights into the significant increase in ozone during COVID-19 in a typical urban city of China

Abstract

Abstract. The outbreak of COVID-19 promoted strict restrictions to human activities in China, which led to a dramatic decrease in most air pollutant concentrations (e.g., PM2.5, PM10, NOx, SO2 and CO). However, an obvious increase in ozone (O3) concentrations was found during the lockdown period in most urban areas of China. In this study, we conducted field measurements targeting ozone and its key precursors by utilizing a novel proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) in Changzhou, which is representative of the Yangtze River Delta (YRD) city cluster of China. We further applied the integrated methodology including machine learning, an observation-based model (OBM) and sensitivity analysis to obtain insights into the reasons causing the obvious increase in ozone. Major findings include the following: (1) by deweathered calculation, we found changes in precursor emissions contributed 1.46 ppbv to the increase in the observed O3 during the full-lockdown period in 2020, while meteorology constrained 3.0 ppbv of O3 in the full-lockdown period of 2019. (2) By using an OBM, we found that although a significant reduction in O3 precursors was observed during the full-lockdown period, the photochemical formation of O3 was stronger than that during the pre-lockdown period. (3) The NOx/VOC ratio dropped dramatically from 1.84 during the pre-lockdown to 0.79 in the full-lockdown period, which switched O3 formation from a VOC-limited regime to the boundary of a NOx- and VOC-limited regime. Additionally, box model results suggested that the decrease in the NOx/VOC ratio during the full-lockdown period could increase the mean O3 by 2.4 ppbv. Results of this study give insights into the relationship between O3 and its precursors in urban area and demonstrate reasons for the obvious increase in O3 in most urban areas of China during the COVID-19 lockdown period. This study also underlines the necessity of controlling anthropogenic oxygenated volatile organic compounds (OVOCs), alkenes and aromatics in the sustained campaign of reducing O3 pollution in China.

The impact of COVID-19 lockdown on ozone budget and radical chemistry in a typical industrial city of China

“…It was supposed that the solar radiation in winter was much lower than that in summer and autumn (Jin et al, 2005;Tang et al, 2010). However, AOC in our study was significantly higher than that during the same period in Changzhou (Zhang et al, 2022a). As shown in Figure 5, the contribution of OH to AOC reached 85% during the whole study period, and thus the higher OH concentration in Tangshan was responsible for the higher AOC compared with Changzhou.…”

Insights on Air Pollution During COVID-19: A Review

“…In addition, the ambient concentration and chemistry are largely regulated via meteorological factors (wind speed, wind direction, relative humidity, planetary boundary layer or mixing height) of the regions (Kumar and Yadav 2016 ; Karle et al 2021 ). The study conducted over the Yangtze River Delta (YRD) city cluster of China to observe the effect of source and meteorology on ozone formation reported 5.1 ppbv contribution for ozone formation regulated via precursor mediated while 0.5 ppbv contribution via meteorological factor (Zhang et al 2021a ). The other study carried out in Handan and the industrial city in China suggests that ozone formation in the ambient atmosphere is a combined effect of reduction in source and meteorology (Yao et al 2021 ).…”

“…The variation in pollutants reduction during the lockdown period could be due to variations in geographical location, meteorological conditions, and atmospheric chemistry. Recently, it has been observed that ozone concentration level in different cities increases during the lockdown period due to alteration in atmospheric chemistry and emission pattern (Zoran et al 2020 ; Zheng et al 2020 ; Zhang et al 2021a ). The tropospheric ozone formation is largely governed via NO x -VOC S -HO x cycle in the atmosphere.…”

Risk tradeoffs between nitrogen dioxide and ozone pollution during the COVID-19 lockdowns in the Greater Bay area of China

“…Control of O 3 pollution is challenging, partly due to the non-linear connections between O 3 and its precursors, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs) ( de Foy et al, 2020 ; Zavala et al, 2020 ). Based on the reactivity of O 3 to its precursors, the photochemical regime of O 3 formation can be classified into categories such as NO x -limited and VOC-limited ( Zhang et al, 2022 ). Due to high NO x emissions, dominant O 3 formation regime in urban areas of China is believed to be VOC-limited ( Ding et al, 2013 ; Shao et al, 2009 ).…”