Rationale: The possible effect of Particulate Matter (PM₁₀ and PM_2.5 of diameter 10 and 2.5 µm respectively) levels on Covid-19 mortality is now well established. However, time-evolution of Covid-19 mortality according to PM_2.5 levels has been scarcely investigated.

Aim: We conducted a detailed data analysis to better understand such relation by considering 16 representative locations in Europe (81 million people) with mean PM_2.5 levels (µg/m³) from low to high. PM_2.5 (as assessed through various methods) and Covid-19 mortality data (Johns Hopkins University website) were considered.

Results: The trend of Covid-19 mortality vs. PM_2.5 level varied among locations (Figure 1); the estimated mean value was a 40±20% mortality increase per 1 µg.m-3 PM_2.5 increase. The stronger the positive gradient of the pollution peak, the stronger the positive gradient of the Covid-19 mortality.                                   Trend evolution of Covid-19 mortality per million inhabitants vs. PM_2.5 

Exposure to several PM peaks during about a 2-month period was the main contributor to Covid-19 mortality increases.  

Conclusion: Our data confirm a temporal relation between PM2.5 exposure and COVID-19 mortality. Number-concentrations of PM should be used in the future rather than the PM2.5 mass-concentrations, with the consideration of PM composition to better explain this finding.