A global observational analysis to understand changes in air quality during exceptionally low anthropogenic emission conditions - Université Paris-Est-Créteil-Val-de-Marne Access content directly
Journal Articles Environment International Year : 2021

A global observational analysis to understand changes in air quality during exceptionally low anthropogenic emission conditions

Ranjeet Sokhi (1) , Vikas Singh (2, 3) , Xavier Querol (4) , Sandro Finardi (5) , Admir Créso Targino , Maria de Fatima Andrade (6) , Radenko Pavlovic (7) , Rebecca Garland (8) , Jordi Massagué (4, 9) , Shaofei Kong (10) , Alexander Baklanov (11) , Lu Ren , Oksana Tarasova (11) , Greg Carmichael (12) , Vincent-Henri Peuch (13) , Vrinda Anand (14) , Graciela Arbilla (15) , Kaitlin Badali (16) , Gufran Beig (14) , Luis Carlos Belalcazar (17) , Andrea Bolignano , Peter Brimblecombe (18) , Patricia Camacho (19) , Alejandro Casallas (20, 21) , Jean-Pierre Charland (16) , Jason Choi (22) , Eleftherios Chourdakis (23) , Isabelle Coll (24) , Marty Collins , Josef Cyrys (25) , Cleyton Martins da Silva (26) , Alessandro Domenico Di Giosa , Anna Di Leo , Camilo Ferro (21) , Mario Gavidia-Calderon (27) , Amiya Gayen (28) , Alexander Ginzburg (29) , Fabrice Godefroy , Yuri Alexandra Gonzalez (30) , Marco Guevara-Luna (31) , Sk. Mafizul Haque (28) , Henno Havenga (32) , Dennis Herod (16) , Urmas Hõrrak (33) , Tareq Hussein (34) , Sergio Ibarra (35) , Monica Jaimes , Marko Kaasik (33) , Ravindra Khaiwal (36) , Jhoon Kim (37) , Anu Kousa (38) , Jaakko Kukkonen (39, 1) , Markku Kulmala (34) , Joel Kuula (39) , Nathalie La Violette , Guido Lanzani , Xi Liu (40) , Stephanie Macdougall , Patrick Manseau (7) , Giada Marchegiani , Brian Mcdonald (41) , Swasti Vardhan Mishra (28) , Luisa Molina (42) , Dennis Mooibroek (43) , Suman Mor , Nicolas Moussiopoulos (23) , Fabio Murena , Jarkko Niemi , Steffen Noe (44) , Thiago Nogueira , Michael Norman (45) , Juan Luis Pérez-Camaño (46) , Tuukka Petäjä (34) , Stuart Piketh (32) , Aditi Rathod (14) , Ken Reid , Armando Retama , Olivia Rivera , Néstor Rojas (30) , Jhojan Rojas-Quincho (47) , Roberto San José (46) , Odón Sánchez (48) , Rodrigo Seguel (49) , Salla Sillanpää (39) , Yushan Su (50) , Nigel Tapper (51) , Antonio Terrazas , Hilkka Timonen (39) , Domenico Toscano , George Tsegas (23) , Guus J.M. Velders (43) , Christos Vlachokostas (23) , Erika von Schneidemesser (52) , Rajasree Vpm (1) , Ravi Yadav (14) , Rasa Zalakeviciute (53) , Miguel Zavala (42)
1 UH - University of Hertfordshire [Hatfield]
2 Department of Computer Sciences
3 Department of Biostatistics & Med. Informatics
4 IDAEA - Institute of Environmental Assessment and Water Research
6 IAG - Instituto de Astronomia, Geofísica e Ciências Atmosféricas [São Paulo]
7 MSC - Meteorological Service of Canada
8 CSIR - Council for Scientific and Industrial Research [Pretoria]
9 UPC - Universitat Politècnica de Catalunya = Université polytechnique de Catalogne [Barcelona]
10 China University of Geosciences [Beijing]
11 WMO - World Meteorological Organization
12 The University of Iowa, Iowa City, Iowa
13 ECMWF - European Centre for Medium-Range Weather Forecasts
14 IITM - Indian Institute of Tropical Meteorology
15 Universidade Federal do Rio de Janeiro
16 ECCC - Environment and Climate Change Canada
17 LPAS - EPFL Air and Soil Pollution Laboratory
18 NSYSU - National Sun Yat-sen University
20 ICTP - Abdus Salam International Centre for Theoretical Physics [Trieste]
21 Escuela de Ciencias Exactas e Ingenieria, Universidad Sergio Arboleda (Bogota, Columbia)
22 EPA - Environment Protection Authority Victoria
23 LHTEE - Laboratory of Heat Transfer and Environmental Engineering [Thessaloniki]
24 LISA (UMR_7583) - Laboratoire Interuniversitaire des Systèmes Atmosphériques
25 Helmholtz Zentrum München, German Research Centre for Environmental Health, Institute of Epidemiology I, Neuherberg, Germany
26 Universidade Veiga de Almeida
27 Departamento de Astronomia Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo
28 University of Calcutta
29 IAP - A.M.Obukhov Institute of Atmospheric Physics
30 UNAL - Universidad Nacional de Colombia [Bogotà]
31 UNAD - Universidad Nacional Abierta y a Distancia
32 Unit for Environmental Sciences and Management, Potchefstroom Campus, North-West University, Private Bag X6001, Potchefstroom, 2520, South Africa
33 University of Tartu
34 INAR - Institute for Atmospheric and Earth System Research
35 Departamento de Ciencias Atmosfericas [São Paulo]
36 Department of Community Medicine and School of Public Health, Post Graduate /nƐƟƚƵƚĞ of Medical ĚƵcĂƟŽn and Research, Chandigarh, India
37 Yonsei University
38 HSY - Helsinki Regional Environmental Services Authority
39 FMI - Finnish Meteorological Institute
40 CUG - China University of Geosciences [Wuhan]
41 NOAA - National Oceanic and Atmospheric Administration
42 MCE2 - Molina Center for the Energy and the Environment
43 RIVM - National Institute for Public Health and the Environment [Bilthoven]
44 EMU - Estonian University of Life Sciences
45 Environment and Health Administration, City of Stockholm
46 Technical University of Madrid
47 National Service of Hydrology and Meteorology of Peru
48 UNTELS - Universidad Nacional Tecnológica de Lima Sur
49 Center for Climate Change and Resilience Research (CR2)
50 Environmental Monitoring and Reporting Branch
51 School of Earth, Atmosphere and Environment, Monash University
52 IASS - Institute for Advanced Sustainability Studies [Potsdam]
53 UDLA - Universidad de Las Américas [Ecuador]
Sandro Finardi
  • Function : Author
Admir Créso Targino
  • Function : Author
Lu Ren
  • Function : Author
Andrea Bolignano
  • Function : Author
Marty Collins
  • Function : Author
Alessandro Domenico Di Giosa
  • Function : Author
Anna Di Leo
  • Function : Author
Fabrice Godefroy
  • Function : Author
Monica Jaimes
  • Function : Author
Marko Kaasik
  • Function : Author
Jhoon Kim
  • Function : Author
Nathalie La Violette
  • Function : Author
Guido Lanzani
  • Function : Author
Stephanie Macdougall
  • Function : Author
Giada Marchegiani
  • Function : Author
Suman Mor
  • Function : Author
Fabio Murena
  • Function : Author
Jarkko Niemi
  • Function : Author
Thiago Nogueira
  • Function : Author
Ken Reid
  • Function : Author
Armando Retama
  • Function : Author
Olivia Rivera
  • Function : Author
Antonio Terrazas
  • Function : Author
Domenico Toscano
  • Function : Author


This global study, which has been coordinated by the World Meteorological Organization Global Atmospheric Watch (WMO/GAW) programme, aims to understand the behaviour of key air pollutant species during the COVID-19 pandemic period of exceptionally low emissions across the globe. We investigated the effects of the differences in both emissions and regional and local meteorology in 2020 compared with the period 2015–2019. By adopting a globally consistent approach, this comprehensive observational analysis focuses on changes in air quality in and around cities across the globe for the following air pollutants PM2.5, PM10, PMC (coarse fraction of PM), NO2, SO2, NOx, CO, O3 and the total gaseous oxidant (OX = NO2 + O3) during the pre-lockdown, partial lockdown, full lockdown and two relaxation periods spanning from January to September 2020. The analysis is based on in situ ground-based air quality observations at over 540 traffic, background and rural stations, from 63 cities and covering 25 countries over seven geographical regions of the world. Anomalies in the air pollutant concentrations (increases or decreases during 2020 periods compared to equivalent 2015–2019 periods) were calculated and the possible effects of meteorological conditions were analysed by computing anomalies from ERA5 reanalyses and local observations for these periods. We observed a positive correlation between the reductions in NO2 and NOx concentrations and peoples’ mobility for most cities. A correlation between PMC and mobility changes was also seen for some Asian and South American cities. A clear signal was not observed for other pollutants, suggesting that sources besides vehicular emissions also substantially contributed to the change in air quality. As a global and regional overview of the changes in ambient concentrations of key air quality species, we observed decreases of up to about 70% in mean NO2 and between 30% and 40% in mean PM2.5 concentrations over 2020 full lockdown compared to the same period in 2015–2019. However, PM2.5 exhibited complex signals, even within the same region, with increases in some Spanish cities, attributed mainly to the long-range transport of African dust and/or biomass burning (corroborated with the analysis of NO2/CO ratio). Some Chinese cities showed similar increases in PM2.5 during the lockdown periods, but in this case, it was likely due to secondary PM formation. Changes in O3 concentrations were highly heterogeneous, with no overall change or small increases (as in the case of Europe), and positive anomalies of 25% and 30% in East Asia and South America, respectively, with Colombia showing the largest positive anomaly of ~70%. The SO2 anomalies were negative for 2020 compared to 2015–2019 (between ~25 to 60%) for all regions. For CO, negative anomalies were observed for all regions with the largest decrease for South America of up to ~40%. The NO2/CO ratio indicated that specific sites (such as those in Spanish cities) were affected by biomass burning plumes, which outweighed the NO2 decrease due to the general reduction in mobility (ratio of ~60%). Analysis of the total oxidant (OX = NO2 + O3) showed that primary NO2 emissions at urban locations were greater than the O3 production, whereas at background sites, OX was mostly driven by the regional contributions rather than local NO2 and O3 concentrations. The present study clearly highlights the importance of meteorology and episodic contributions (e.g., from dust, domestic, agricultural biomass burning and crop fertilizing) when analysing air quality in and around cities even during large emissions reductions. There is still the need to better understand how the chemical responses of secondary pollutants to emission change under complex meteorological conditions, along with climate change and socio-economic drivers may affect future air quality. The implications for regional and global policies are also significant, as our study clearly indicates that PM2.5 concentrations would not likely meet the World Health Organization guidelines in many parts of the world, despite the drastic reductions in mobility. Consequently, revisions of air quality regulation (e.g., the Gothenburg Protocol) with more ambitious targets that are specific to the different regions of the world may well be required.
Fichier principal
Vignette du fichier
1-s2.0-S0160412021004438-main.pdf (14.14 Mo) Télécharger le fichier
Origin : Publisher files allowed on an open archive
Licence : CC BY NC ND - Attribution - NonCommercial - NoDerivatives

Dates and versions

hal-04480899 , version 1 (02-03-2024)



Ranjeet Sokhi, Vikas Singh, Xavier Querol, Sandro Finardi, Admir Créso Targino, et al.. A global observational analysis to understand changes in air quality during exceptionally low anthropogenic emission conditions. Environment International, 2021, 157, pp.106818. ⟨10.1016/j.envint.2021.106818⟩. ⟨hal-04480899⟩
119 View
4 Download



Gmail Facebook X LinkedIn More