The average annual PM2.5 level in London in 2018 was 11mcg/m3, 1mcg/m3 above the guideline limit set by the World Health Organisation.
London has been the worst hit area in the UK for Covid-19 deaths, accounting for more than 1,700 of the total 7,097 deaths.
The authors of the study said that the findings “underscore the importance of continuing to enforce existing air pollution regulations during the COVID-19 crisis.”
The UK government has vowed to tackle the sources of PM2.5, which include road traffic and domestic wood and coal burning.
Researchers from the EU satellite Copernicus, which tracks air pollution, announced last week that they would be contributing data to exploring the role that particulate matter might play in carrying the virus.
It came after a study from the University of Bologna, in Italy, found that the death toll was higher in the Po valley, where air pollution is particularly bad.