1. The study analyzed changes in air quality and population exposure to air pollution in 62 global cities resulting from COVID-19 lockdown measures. 2. It found reductions of 20-60% for NO2 and up to 40% for PM2.5 in some cities, but also increases for PM2.5 in other cities. Ozone increased in most cities due to decreased titration from other pollutants. 3. While lockdown measures were effective at reducing NO2 levels to comply with EU and WHO guidelines, PM2.5 reductions were more limited and regional cooperation is still needed to reach WHO PM guidelines due to factors like long-range transport and biomass burning.

1. 1
WMO/GAW Coordinated study on impacts of
covid-19 lockdown measures on air quality: an
observational and modelling analysis
Ranjeet Sokhi, Vikas Singh, Xavier Querol, Jordi Massague, Sandro Finardi, Admir Créso Targino, Maria de
Fatima Andrade, Rebecca Garland, Radenko Pavlovic, Shaofei Kong, Alexander Baklanov, Lu Ren
(observation analysis coordination group) and many global contributors.

2. 2
WMO/GAW Coordinated study
Aim: To understand how air quality and population exposure has changed in cities
as a result of measures to control the spread of the COVID-19 virus
Specific objectives:
1. To quantify the changes in air pollutant concentrations on local to regional scales
2. To understand how the balance and mix of local and regional contributions has
shifted for air pollutant species
3. To understand how changes in air quality are influenced by factors e.g. location,
characteristics of cities, demography, emissions, weather, climate
4. To extend our understanding of the effectiveness and implementation of
strategies and measures to improve urban air quality

3. 3
Italian participation to the initiative
Observational analysis
• Sandro Finardi (ARIANET)
• Anna Di Leo e Guido Lanzani (ARPA Lombardia)
• Giada Marchegiani e Alessandro Di Giosa (ARPA Lazio)
• Fabio Murena (Università degli studi di Napoli "Federico II")
Modelling analysis
• Antonio Piersanti (ENEA)
• Sandro Finardi (ARIANET), observing

4. 4
62
Cities
Observational analysis

5. 5
Observational analysis
Five period defined from Feb 2020:
• Pre-lockdown
• Partial lockdown
• Full lockdown
• Partial relaxation
• Full relaxation
Air pollutants: PM10, PM2.5, NO, NO2, CO, SO2, O3
Station types:
Type -Traffic or Background; Subtypes -urban, suburban, industrial, rural
 70% of ratified data (official data).
Meteorological influences evaluation:
Average of five years of historic data used for comparison: 2015 -2019
Meteorological variables: u (10m), T (2m), RH (2m), radiation, precipitation
Meteorological analyses: ERA5 (monthly anomalies)

6. 6
Lockdown periods

7. 7
Air quality anomaly: NO2
China
India
Korea
Europe
N America
S America
S Africa

8. Air quality anomaly: PM2.5
Secondary PM
Production in
northern China
T. Le et al.,
Science
10.1126/science.
abb7431 (2020).
China
India
Korea
Europe
N America
S America
S Africa

9. Air quality anomaly: O3
China
India
Korea
Europe
N America
S America
S Africa

10. 10
Continental summary

11. 11
Ozone: urban & rural background variations
25/02-31/07/2020
Cipro - Urban background
Guido - Rural background
50 ppb level

12. 12
Concluding remarks
• Estimated changes in NO2, NOx, PM2.5, PM10, PMC and O3 for 62 global cities
• Worldwide relevant reduction of 20-60% in NO2
• Limited reduction in PM2.5, up to 40% in some cities but with relevant regional differences,
e.g. in other cities an increase is recorded. Secondary PM production has been identified in
northern China, while biomass burning, and long-range transport is expected to have an
increased weight
• O3 shows an increase in most cities, mainly due to the decreased titration, regional O3
variation to be investigated including summer ozone season
• Local policies on transport related emissions can reach compliance of EU and WHO NO2 limits
• WHO PM guideline values do not seem reachable on the basis transport measures and local
scale policies, wood burning for residential heating is a relevant contribution to be addressed,
but regional/international policies and measures are desirable and needed for LRT impact.