Unexpected rise of ozone in urban and rural areas, and sulfur dioxide in rural areas during the coronavirus city lockdow
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ORIGINAL PAPER
Unexpected rise of ozone in urban and rural areas, and sulfur dioxide in rural areas during the coronavirus city lockdown in Hangzhou, China: implications for air quality Liqiang Wang1 · Mengying Li1 · Shaocai Yu1,2 · Xue Chen1 · Zhen Li1 · Yibo Zhang1 · Linhui Jiang1 · Yan Xia1 · Jiali Li1 · Weiping Liu1 · Pengfei Li3 · Eric Lichtfouse4,5 · Daniel Rosenfeld6 · John H. Seinfeld2 Received: 13 May 2020 / Accepted: 1 June 2020 © Springer Nature Switzerland AG 2020
Abstract The outbreak of coronavirus named COVID-19, initially identified in Wuhan, China in December 2019, has spread rapidly at the global scale. Most countries have rapidly stopped almost all activities including industry, services and transportation of goods and people, thus decreasing air pollution in an unprecedented way, and providing a unique opportunity to study air pollutants. While satellite data have provided visual evidence for the global reduction in air pollution such as nitrogen dioxide (NO2) worldwide, precise and quantitative information is missing at the local scale. Here we studied changes in particulate matter (PM2.5, PM10), carbon monoxide (CO), NO2, sulfur dioxide (SO2) and ozone (O3) at 10 urban sites in Hangzhou, a city of 7.03 million inhabitants, and at 1 rural site, before city lockdown, January 1–23, during city lockdown, January 24-February 15, and during resumption, February 16–28, in 2020. Results show that city lockdown induced a sharp decrease in PM2.5, PM10, CO, and N O2 concentrations at both urban and rural sites. The N O2 decrease is explained by reduction in traffic emissions in the urban areas, and by lower regional transport in rural areas during lockdown, as expected. SO2 concentrations decreased from 6.3 to 5.3 μg m−3 in the city, but increased surprisingly from 4.7 to 5.8 μg m−3 at the rural site: this increase is attributed both to higher coal consumption for heating and emissions from traditional fireworks of the Spring Eve and Lantern Festivals during lockdown. Unexpectedly, O3 concentrations increased by 145% from 24.6 to 60.6 μg m−3 in the urban area, and from 42.0 to 62.9 μg m−3 in the rural area during the lockdown. This finding is explained by the weakening of chemical titration of O3 by NO due to reductions of NOx fresh emissions during the non-photochemical reaction period from 20:00 PM to 9:00 AM (local time). During the lockdown, compared to the same period in 2019, the daily average concentrations in the city decreased by 42.7% for P M2.5, 47.9% for P M10, 28.6% for S O2, 22.3% for CO and 58.4% for N O2, which is obviously explained by the absence of city activities. Overall, we observed not only the expected reduction in some atmospheric pollutants (PM, SO2, CO, NO2), but also unexpected increases in SO2 in the rural areas and of ozone (O3) in both urban and rural areas, the latter being paradoxically due to the reduction in nitrogen oxide levels. In other words, the city lockdown has improved air quality by reducing PM2.5, PM10, CO, and NO2, but has
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