After dropping off due to Covid-19 restrictions, air pollution levels in China are returning to pre-pandemic levels, according to satellite imagery and data released by the European Space Agency.

According to the ESA, nitrogen dioxide concentrations in Beijing dropped by around 35% between February 2019 and 2020, as factories and other industries shut down before returning to similar levels in February 2021.

"Now, more than one year later, as restrictions have eased, the average level of air pollutants has rebounded and is on the rise again," the ESA said.

In Chongqing, in the southwest of the country, the post-pandemic nitrogen dioxide concentrations have almost doubled from the pre-Covid numbers.

The ESA has said they expect similar trends elsewhere in the coming weeks and months.

"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," said Claus Zehner, ESA's Copernicus Sentinel-5P mission manager.

"In the coming weeks and months, we expect increases of nitrogen dioxide concentrations also over Europe."

Images show nitrogen dioxide concentrations over China in February 2019, February 2020 and February 2021.