The Impact of the Wuhan Covid-19 Lockdown on Air Pollution and Health: A Machine Learning and Augmented Synthetic Contro
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The Impact of the Wuhan Covid‑19 Lockdown on Air Pollution and Health: A Machine Learning and Augmented Synthetic Control Approach Matthew A. Cole1 · Robert J R Elliott1 · Bowen Liu1 Accepted: 13 July 2020 © Springer Nature B.V. 2020
Abstract We quantify the impact of the Wuhan Covid-19 lockdown on concentrations of four air pollutants using a two-step approach. First, we use machine learning to remove the confounding effects of weather conditions on pollution concentrations. Second, we use a new augmented synthetic control method (Ben-Michael et al. in The augmented synthetic control method. University of California Berkeley, Mimeo, 2019. https://arxiv.org/pdf/1811.04170 .pdf) to estimate the impact of the lockdown on weather normalised pollution relative to a control group of cities that were not in lockdown. We find NO2 concentrations fell by as much as 24 μg/m3 during the lockdown (a reduction of 63% from the pre-lockdown level), while PM10 concentrations fell by a similar amount but for a shorter period. The lockdown had no discernible impact on concentrations of SO2 or CO. We calculate that the reduction of NO2 concentrations could have prevented as many as 496 deaths in Wuhan city, 3368 deaths in Hubei province and 10,822 deaths in China as a whole. Keywords Air pollution · Covid-19 · Machine learning · Synthetic control · Health JEL Classification Q53 · Q52 · I18 · I15 · C21 · C23
1 Introduction At the time of writing, much of the world remains in the grip of the Covid-19 pandemic. The full social and economic consequences of the pandemic and its restrictions on our dayto-day activities will be far-reaching and will take time to fully identify and quantify. The primary method of slowing the infection rate has been to impose strict social distancing
* Robert J R Elliott [email protected] Matthew A. Cole [email protected] Bowen Liu [email protected] 1
Department of Economics, University of Birmingham, Birmingham, UK
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regulations known as ‘lockdowns’ where people are restricted to their own homes and all but essential economic activity ceases. Interestingly, one consequence of these lockdowns that became apparent from an early stage was a perceived improvement in air quality. As many shops and businesses closed, industrial activity and vehicle use in cities fell dramatically and reports emerged of pollution levels being considerably below those experienced in normal conditions. These reports first emerged in China but have since appeared in many other countries (New York Times 2020; Guardian 2020; Independent 2020; Space 2020). Such improvements in air quality and the likely associated health benefits have raised the prospect of an unlikely silver lining to the otherwise overwhelmingly negative impacts of the pandemic. These apparent improvements in air quality have, however, raised a number of questions. First, which pollutants have actually fallen? Most media reports refer only to a reduction in Nitrogen Dioxide (NO2 ) with no discussi
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