Global association between satellite-derived nitrogen dioxide (NO2) and lockdown policies under the COVID-19 pandemic

Abstract

The COVID-19 pandemic has severely affected various aspects of life, at different levels and in different countries on almost every continent. In response, many countries have closed their borders and imposed lockdown policies, possibly bringing benefits to people's health with significantly less emission from air pollutants. Currently, most studies or reports are based on local observations at the city or country level. There remains a lack of systematic understanding of the impacts of different lockdown policies on the air quality from a global perspective. This study investigates the impacts of COVID-19 pandemic towards global air quality through examining global nitrogen dioxide (NO 2 ) dynamics from satellite observations between 1 January and 30 April 2020. We used the Apriori algorithm, an unsupervised machine learning method, to investigate the association among confirmed cases of COVID-19, NO 2 column density, and the lockdown policies in 187 countries. The findings based on weekly data revealed that countries with new cases adopted various lockdown policies to stop or prevent the virus from spreading whereas those without tended to adopt a wait-and-see attitude without enforcing lockdown policies. Interestingly, decreasing NO 2 concentration due to lockdown was associated with international travel controls but not with public transport closure. Increasing NO 2 concentration was associated with the “business as usual” strategy as evident from North America and Europe during the early days of COVID-19 outbreak (late January to early February 2020), as well as in recent days (in late April) after many countries have started to resume economic activities. This study enriches our understanding of the heterogeneous patterns of global associations among the COVID-19 spreading, lockdown policies and their environmental impacts on NO 2 dynamics.

Unintended health and societal consequences of international travel measures during the COVID-19 pandemic: a scoping review

“…Of the included studies, nine used quasi-experimental designs, including eight interrupted time series studies 33–40 and one difference-in-difference study. 41 We also identified two observational studies, 42 , 43 two mathematical modelling studies, 44 , 45 six qualitative studies 46–51 and four mixed methods studies. 52–55 …”

“… 33 , 36 , 37 , 46 , 49 , 50 Eight studies analysed the effects of international travel measures implemented by multiple countries. 35 , 38–41 , 44 , 45 , 55 Three studies did not focus on specific countries or settings. 34 , 42 , 43 …”

“… 46 However, in the majority of studies, this was either not applicable or not specified. 33–43 , 45 , 47 , 49–51 , 53–55 Most studies did not differentiate between specific modes of travel (i.e. air, land or sea).…”

“…A variety of different travel measures were investigated, often in combination. Seven studies provided information on the closure of national borders, 33 , 36 , 43 , 47 , 53–55 six looked at international travel restrictions, 33 , 41 , 42 , 45 , 49 , 50 and three investigated quarantine of travellers crossing national borders. 49 , 51 , 52 No studies were identified that looked at entry and/or exit screening at national borders exclusively (i.e.…”

The Improvement of Air Quality and Associated Mortality during the COVID-19 Lockdown in One Megacity of China: An Empirical Strategy

“…Although previous studies have shown improvements in air pollution during the lockdown period, these changes measured during the lockdown period could not represent the effect of the lockdown well because of confounders such as secular trends and weather influences [7,8]. Previous studies have assessed the health effects associated with air pollution during the Asia-Pacific Economic Cooperation (APEC) [9] and the 2015 China large-scale military parade periods [10], and one possible problem faced in these studies, as well as recent studies [11,12] during COVID, is a bias against the real effects of policies on air pollutants.…”