Declines in Atmospheric Pollution During the COVID-19 Lockdown Are Consistent With Contraction in Economic Output

Authors: Christoph Keller (NASA GMAO / USRA), Mat Evans (National Centre for Atmospheric Sciences, University of York)

Nitrogen oxides (NOx=NO+NO2) are an important air pollutant emitted during the combustion of fossil fuel for industry, transport and domestic activities [Streets et al., 2013, Duncan et al., 2016]. Because of these sources and its short lifetime, concentrations of nitrogen oxides respond rapidly to changes in economic activities. This is reflected in the sharp decline in NO2 concentration observed in the wake of the COVID-19 pandemic (see for example the reductions in NO2 observed from the NASA Ozone Monitoring Instrument (OMI) satellite (, Liu et al., 2020).

However, NO2 concentrations also change due to the weather and season and these factors need to be accounted for before drawing conclusions about causality. One approach is to combine near real-time NASA model simulations with surface observations made by air quality monitoring stations. A machine learning algorithm can be used to understand the historical relationship between observed local air pollution concentrations and the model and this can be used to calculate the concentration of NO2 that would have been expected had COVID-19 not occurred (Keller et al., 2020). Applying this to 4,778 air quality monitoring sites in 46 countries shows that NO2 concentrations declined by up to 45% during the second quarter of 2020 relative to the business as usual scenario (Figure 1).

Figure 1 graph
Figure 1. Concentration of observed surface NO2 relative to model simulations of surface NO2 for selected countries

Given the major sources of NO2, a close relationship between the impact of COVID-19 on NO2 concentration and economic activity is to be expected. Figure 2 shows the change in detrended national gross domestic product (GDP, obtained from compared to the change in NO2 concentration shown in Figure 1 averaged over the 1st or 2nd quarter of 2020.

Figure 2 graph
Figure 2. Gross Domestic Product change vs. NO2 change in first two quarters of 2020

Only countries that were significantly impacted by COVID-19 for either of those quarters and with available GDP data are shown. To allow for better GDP comparisons against surface NO2 (and also between countries), the nominal GDP value of each country has been detrended based on least squares linear regression of the 2017-2019 GDP growth rates. The thus obtained NO2 to GDP relationship suggests that there is a strong, linear relationship between the change in the GDP and change in the country level NO2 concentration, with a 10% percentage decrease in NO2 concentrations corresponding to an average output contraction of 5.3% relative to the country’s baseline GDP. Detailed results for all analyzed countries are summarized in Table 1.

Table 1: Summary of results. Listed are the NO2 anomaly estimated from observations and model simulations (see Keller et al., 2020); annual GDP growth rate (from, as of August 17 2020); GDP adjusted for 2017-2019 GDP trend; and detrended GDP values obtained from the GDP vs. NO2 fit.
Period Country NO2 anomaly Reported GDP Detrended GDP Predicted GDP
Q1-2020 China -22 -6.8 -12.6 -13.2
Q1-2020 Hong Kong -7.8 -8.9 -4.9 -5.6
Q1-2020 Italy -10.7 -5.4 -5.4 -7.1
Q1-2020 Spain -11.5 -4.1 -5.8 -7.5
Q1-2020 Taiwan -7 1.6 -1.1 -5.1
Q2-2020 Australia -10.5 n/a n/a -7
Q2-2020 Austria -23.3 -12.8 -13.5 -13.8
Q2-2020 Belgium -23.5 -14.5 -15.9 -14
Q2-2020 Bosnia and Herzegovina -14.9 n/a n/a -9.4
Q2-2020 Brazil 5.7 n/a n/a 1.6
Q2-2020 Bulgaria -14.5 -8.2 -11.6 -9.2
Q2-2020 Canada -21.8 n/a n/a -13.1
Q2-2020 Chile -7.2 n/a n/a -5.3
Q2-2020 China -4.7 3.2 -2.4 -3.9
Q2-2020 Colombia -35.2 -15.7 -19.7 -20.2
Q2-2020 Croatia -38.2 n/a n/a -21.8
Q2-2020 Cyprus -40.8 -11.9 -14.5 -23.1
Q2-2020 Czech Republic -12 -10.7 -12.6 -7.8
Q2-2020 Denmark -18.6 n/a n/a -11.3
Q2-2020 Ecuador -49.1 n/a n/a -27.6
Q2-2020 Estonia -19.6 n/a n/a -11.8
Q2-2020 Finland -26.7 -4.9 -5.1 -15.7
Q2-2020 France -33.5 -19 -19.9 -19.3
Q2-2020 Germany -18.1 -11.7 -11.3 -11.1
Q2-2020 Greece -17.9 n/a n/a -11
Q2-2020 Hong Kong -7 -9 -3.9 -5.1
Q2-2020 Hungary -15.8 -13.6 -18.4 -9.8
Q2-2020 Iceland -24.2 n/a n/a -14.3
Q2-2020 India -39.4 n/a n/a -22.4
Q2-2020 Ireland -37.1 n/a n/a -21.2
Q2-2020 Italy -32.7 -17.3 -17.1 -18.9
Q2-2020 Japan -21.7 -9.9 -10.2 -13
Q2-2020 Latvia -18.4 -9.8 -11 -11.2
Q2-2020 Lithuania -19.2 -3.8 -7.8 -11.6
Q2-2020 Luxembourg -29.2 n/a n/a -17
Q2-2020 Macedonia -21.2 n/a n/a -12.7
Q2-2020 Malta -34.8 n/a n/a -20
Q2-2020 Netherlands -18.1 -9.3 -10.5 -11.1
Q2-2020 Norway -22.6 n/a n/a -13.5
Q2-2020 Poland -14.6 -8.2 -11.3 -9.2
Q2-2020 Portugal -26.7 -16.5 -18.3 -15.7
Q2-2020 Romania -15.8 -10.5 -14.3 -9.8
Q2-2020 Serbia -36.1 n/a n/a -20.7
Q2-2020 Slovakia -17.3 -12.1 -13.3 -10.6
Q2-2020 Spain -39.9 -22.1 -23.6 -22.7
Q2-2020 Sweden -19 -8.2 -8.5 -11.5
Q2-2020 Switzerland -21.4 n/a n/a -12.8
Q2-2020 Taiwan -5.8 -0.7 -3.4 -4.5
Q2-2020 Thailand -19.8 -12.2 -13 -12
Q2-2020 United Kingdom -36.3 -21.7 -23.1 -20.8
Q2-2020 United States -23.2 -9.5 -11.4 -13.8

These results highlight the strong relationship between atmospheric NO2 and human economic activity, indicating that a sustainable reduction in NO2 pollution can only be achieved if this strong link between NOx emissions and economic output can be broken.

See the related article: "NASA Model Reveals How Much COVID-related Pollution Levels Deviated from the Norm".


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