COVID-19 Lockdown Cleans Polluted Air in Italy

The use of the Google Earth Engine platform to study air pollution provided interesting data on Italy related to the coronavirus pandemic.

Co-author: Vasily Lobanov

A screenshot from CompareNO2 app showing a sudden change in NO₂ level over Northern Italy between Jan 2020 (left) and Feb/Mar 2020 (right).

Air Pollution Monitoring and Coronavirus

A new coronavirus disease (COVID-19) appeared in at least 167 countries by March 20, 2020.¹ Millions of people have been quarantined since the end of 2019, which became the largest event in human history of such kind.² ³ As a consequence, a worldwide economic recession is taking place around the world.⁴ While governments are attempting to stop the operation of enterprises and vehicles to curb the spread of infection, people are burning less fuel in power plants, airplanes, cars, and trucks. As a result, the amount of nitrogen dioxide (NO₂) entering the atmosphere is reducing. Similar processes with air pollution decrease also occur during national or cultural holidays and have already been studied.⁵

Recently, NASA and ESA experts showed the correlation between a reduction in NO₂ air pollution and a decrease in production rate in China during the outbreak of coronavirus.

Airborne Nitrogen Dioxide Plummets Over China

The relationship between low emissions and the fact that people move a little or work less is undeniable. But these data can help dealing with an inverse task: to assess the degree of economic activity of a territory by the level of pollution measured from space. For many years, a significant problem has been the study of the relationship between human well-being and the measured environmental characteristics. Each of these parameters can respond differently to social and economic phenomena. Therefore, their study should be as comprehensive as possible. Some links between indicators of economic activity and the environment, for example, were presented in a 1995 American article comparing per capita income with urban air pollution, oxygen conditions, and pollution of river basins with feces and heavy metals.⁶ However, the lack of data has always limited the scope of any such research.

The advances of the latest Earth remote sensing satellites allow scientists to accurately evaluate the various parameters of our planet on its entire surface with high resolution and frequency. And it turns out that the accumulated big data on atmospheric pollution can be useful not only to climatologists and environmentalists but also to researchers of socio-economic processes and phenomena.

CompareNO2

I have been developing the ideas of foreign colleagues from NASA and ESA together with Vasily Lobanov, a director of the Remote Sensing Center at RUDN University, Russia. We are making an interactive web application CompareNO2, which allows estimating the dynamics of nitrogen dioxide emissions in different regions of the world. The goal is to create an open and easy-to-use web app that lowers the entry threshold for researchers studying trace gases. CompareNO2 is powered by the Google Earth Engine platform, which combines a multi-petabyte catalog of satellite imagery and geospatial datasets with planetary analysis capabilities.⁷

Try CompareNO2 to create your own NO₂ visualization.

The source for measuring NO₂ levels is the data of the European satellite Sentinel-5P, equipped with an advanced spectrometer. It collects samples of ozone, nitrogen dioxide, and other atmospheric pollutants with a higher degree of detail than all previous space-borne sensors.⁸ The availability of such rich atmospheric data makes it possible to track pollutants and develop forecasts with high accuracy. Another essential source of information is meteorological datasets from the Hydrometeorological Centers of Russia and NASA, which we implement in the application soon.

Computer animation showing the work of Sentinel-5P in orbit. This satellite is able to measure concentration of various trace gases in the atmosphere.

Italy on Lockdown

CompareNO2 is under active development now, but you can already see some interesting results obtained from it. Let’s check what is happening in Italy and, in particular, Lombardy, one of the most developed regions of this country, which has been severely affected by the epidemic.⁹

In Italy as a whole, from the end of February 2020, when the government introduced restrictive measures, nitrogen dioxide level has decreased on average 1.4 times. In Lombardy, this drop is more pronounced — on average, 2.9 times. Of course, meteorological conditions strongly affect the situation. However, a comparison with the previous year shows a decrease in the amount of NO₂ lower than expected this season.

A time series that records that at the beginning of March 2020, the average NO₂ content in the troposphere above Lombardy dropped 2.9 times compared with the end of February 2020.

With CompareNO2, we analyzed the dynamics of nitrogen dioxide at several points of interest using over 600 of Sentinel-5p images. If you look at point measurements of NO₂ density in individual cities below, you can see an atypical seasonal drop. Note that the maximum concentration of NO₂ happens during the winter, which is partly due to adverse weather conditions preventing self-cleaning of the atmosphere, and accompanied by maximum emissions of thermal power stations. The seasonality of nitrogen dioxide levels is especially noticeable in such large industrial centers as Milan, Verona, and Vicenza. But they all share an unusual drastic decline at the end of February 2020, which corresponds to the time series of maps provided above.

We made this chart in CompareNO2 after the analysis of over 600 Sentinel-5P images that were grouped by 14-days intervals. It shows the variations of the tropospheric vertical column density of NO₂ at various cities in Italy from January 2019 to March 2020. You can notice a drastic non-typical dropdown in Milan, Verona, Vicenza, and Rome, which starts from the end of February 2020.

The data presented on the chart confirms the expected trend. In Milan, by the beginning of March 2020, the NO₂ level fell by 2 times compared to the same period last year, in Verona — by 1.8 times, in Vicenza — by 1.5 times. CompareNO2 allows you to get not olny a set of intriguing maps and animations that journalists like to put in news broadcasts. The value is that you can quantify the dynamics of air pollution at any point on the planet with great detail. Thus, after the end of the pandemic, we plan to use such data to conduct a more serious study to assess the possibility of predicting socio-economic indicators from satellite images.

Experts from various adjacent fields struggle with big data processing and programming issues when trying to extract scientific value from Earth observation data. For such people, we publish training materials on how to create and use data-intensive web applications on the Google Earth Engine platform in our Medium blog called Geospatial Team. Soon we open access to CompareNO2, and you will also be able to study air pollution in regions of your interest.

References

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2. China’s unprecedented quarantine of 11 million people in Wuhan is 3 weeks old. Here’s what it’s like in the isolated city. (15.02.2020). Business Insider
3. Coronavirus: Italy extends emergency measures nationwide. (10.03.2020). BBC
4. Coronavirus: A visual guide to the economic impact. (16.03.2020). BBC
5. Pei-Hua Tan, Chia Chou, Jing-Yi Liang, Charles C.-K. Chou, Chein-Jung Shiu, Air pollution “holiday effect” resulting from the Chinese New Year, Atmospheric Environment, Volume 43, Issue 13, 2009, Pages 2114–2124, ISSN 1352–2310, https://doi.org/10.1016/j.atmosenv.2009.01.037
6. Gene M. Grossman, Alan B. Krueger. (May 1995). Economic Growth and the Environment, The Quarterly Journal of Economics, Volume 110, Issue 2, Pages 353–377, https://doi.org/10.2307/2118443
7. Noel Gorelick, Matt Hancher, Mike Dixon, Simon Ilyushchenko, David Thau, Rebecca Moore. Google Earth Engine: Planetary-scale geospatial analysis for everyone, Remote Sensing of Environment, Volume 202, 2017, Pages 18–27, ISSN 0034–4257, https://doi.org/10.1016/j.rse.2017.06.031
8. Copernicus: Sentinel-5P. ESA eoPortal Directory. Access date: 20.03.2020
9. Luca Piana. L’impatto del coronavirus sull’Italia spa: possibile un danno da 641 miliardi. (16.03.2020). La Repubblica

Image (a satellite over the Earth): ESA.