Observed reduced air pollution over China amidst COVID-19

By Esther Nakkazi

As a result of the reduction in daily traffic and industry activities in China since the COVID-19 outbreak, climate monitoring services have noticed a reduction in air pollution.

The Copernicus Atmosphere Monitoring Service (CAMS) reports that it observed a decrease of fine particulate matter (PM2.5) for the month of February relative to the previous three years. PM2.5 is one of the most important air pollutants regarding health impacts according to the World Health Organization (WHO).

PM2.5 is used to describe particles that are 2.5 micrometres and smaller in size. These particles, either solid, gas or liquid in composition, have potential to pose serious health problems when inhaled into the respiratory system and are known to trigger or worsen chronic diseases and other respiratory problems.

When comparing the difference between the monthly average for February 2020 and the mean of monthly averages for February 2017, 2018 and 2019, it clearly shows that these analyses indicate a reduction of about 20-30 % in surface PM2.5 over large parts of China in February 2020 based on information from the satellite observations, says the CAMS. 

The reduction in PM2.5 can likely be attributed in part to the slow-down in activity due to measures against the COVID-19 spread, the report says.

Vincent-Henri Peuch, Director of CAMS said they do not discount other variables next to the shutdown potentially playing a role in the decrease. For instance, China has actively been trying to reduce emissions, and meteorological variability between different years.

"To subtract these variables out of the equation, we set the duration of three years 2017-2019 to estimate the ‘business as usual’ conditions as a compromise to have a representative estimate of February’s monthly mean, while not considering too long of a period over which emissions vary substantially because of long-term trends,” said Peuch.

CAMS monitors PM2.5 over China by combining observations from satellites with detailed computer models of the atmosphere resulting in daily analyses.

To further substantiate this finding, CAMS also produced the same difference between February 2020 and the February mean for 2017-2019 without using the satellite observations. Because the PM2.5 values are in this case only dependent on the prescribed emissions and the meteorological conditions, it can provide a reference for the difference where satellite information was used as well. 

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