Air quality changed disproportionally across the world urban agglomerations, countries, and regions due to COVID-19 lockdown measures

Abstract

BACKGROUND AND AIM: The COVID-19 response policies had a major impact on air quality (AQ) worldwide. However, limited data availability, diverse political responses, and multiple-factor interactions made the analysis challenging. We aimed to quantify the effect of various COVID-19 response policies on concentration of ambient nitrogen dioxide (NO2) in major world urban agglomerations (UAs), countries, and regions. METHODS: Daily mean NO2 concentrations from January 01, 2019 to July 31, 2020 were collected from 1) 1,267 publicly available ground monitoring sites at 496 UAs across 29 countries, and 2) Sentinel-5P satellite at 1,851 UAs across 143 countries. Eight daily national COVID-19 response actions were retrieved from Oxford’s COVID-19 Government Response Tracker for countries of the world. COVID-19 response action implementations were clustered into three groups: stringent, moderate, and mild policy. Using UA-specific linear regression models, we assessed the association between different policy implementations and NO2 concentrations, adjusting for meteorological variables and time trends. Finally, meta-regression models were applied to aggregate global, regional, and country-specific results. In addition, we examined the effect modification of the association by UA population size. RESULTS:Ground-monitored data suggested that NO2 concentrations decreased by 32% in countries with a stringent policy and by 26% in countries with a moderate policy. No substantial changes occurred in countries with a mild policy. Satellite observations of NO2 were highly correlated with ground-monitored data, and demonstrated that the greatest AQ improvements occurred in the Eastern Mediterranean and Western Pacific regions, but not in Europe or North America. The greatest AQ improvements were observed in more populated areas, especially in UAs with ≥5 million population. CONCLUSIONS:Our study suggests that COVID-19 response policies taken in 2020 led to global reductions in NO2 concentrations. These AQ improvements were most pronounced in countries with more stringent COVID-19 containment policies and in more populated areas. KEYWORDS: COVID-19, Air pollution, Policy, Exposures, Oxides of Nitrogen