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New York/Canadian-Media: Nationwide lockdowns put in place to stop the spread of COVID-19 during early 2020 coincided with a decline in air pollution shown by the data collected from satellites. The reverse situation prevailed one year later with relaxation of restrictions of the lockdown and prevalence of regular activities in some countries when nitrogen dioxide levels bounced back to pre-COVID levels, European Space Agency (ESA) news reports said.
ESA. Image credit: Wikipedia
On 23 January 2020, the world saw the first coronavirus lockdown come into force in Wuhan and similar measures were then put in place worldwide in the following weeks and months which resulted in a significant reduction in air pollutants across China as detected by satellites. including reduced emissions of nitrogen dioxide – a gas that pollutes the air mainly as a result of traffic and the combustion of fossil fuel in industrial processes.
With the ease of restrictions an year later, the average level of air pollutants has rebounded and is on the rise again. The maps below show the monthly average concentrations of nitrogen dioxide, derived from data from the Copernicus Sentinel-5P satellite, in the central and eastern portions of China in February 2019, February 2020 and February 2021. The map shows the fluctuation in levels between the three periods, with dark red indicating high concentrations of nitrogen dioxide.
Nitrogen dioxide concentrations over China. Image credit: Official website of ESA
Nitrogen dioxide concentrations in Beijing, indicated by the data dropped by around 35 percent between February 2019 and 2020 before returning to similar levels in February 2021, whereas in Chongqing, nitrogen dioxide dropped by approximately 45 percent between February 2019 and February 2020, before returning to almost double pre-COVID numbers.
The data is collected by Tropomi instrument on board the Copernicus Sentinel-5P satellite – the first Copernicus mission dedicated to monitoring our atmosphere.
Claus Zehner, ESA’s Copernicus Sentinel-5P mission manager, says, “We expected air pollution to rebound as lockdowns are lifted across the globe. Nitrogen dioxide concentrations in our atmosphere do not depend on human activity alone. Weather conditions such as wind speed and cloud cover also affect those levels, however a large quantity of these reductions are due to restrictions being eased. In the coming weeks and months, we expect increases of nitrogen dioxide concentrations also over Europe.”
Claus continues, “The special features of the Copernicus Sentinel-5P satellite, with its high spatial resolution and accurate ability to observe trace gases compared to other atmospheric satellite missions, allows us to generate these unique nitrogen dioxide concentration measurement maps from space.”
Tropomi instrument, which is used to map a multitude of trace gases such as nitrogen dioxide, ozone, formaldehyde, sulphur dioxide, methane, carbon monoxide and aerosols is carried by the satellite.