PM(2.5) Pollution Strongly Predicted COVID-19 Incidence in Four High-Polluted Urbanized Italian Cities during the Pre-Lockdown and Lockdown Periods

Background: The coronavirus disease in 2019 (COVID-19) heavily hit Italy, one of Europe’s most polluted countries. The extent to which PM pollution contributed to COVID-19 diffusion is needing further clarification. We aimed to investigate the particular matter (PM) pollution and its correlation with COVID-19 incidence across four Italian cities: Milan, Rome, Naples, and Salerno, during the pre-lockdown and lockdown periods. Methods: We performed a comparative analysis followed by correlation and regression analyses of the daily average PM(10), PM(2.5) concentrations, and COVID-19 incidence across four cities from 1 January 2020 to 8 April 2020, adjusting for several factors, taking a two-week time lag into account. Results: Milan had significantly higher average daily PM(10) and PM(2.5) levels than Rome, Naples, and Salerno. Rome, Naples, and Salerno maintained safe PM(10) levels. The daily PM(2.5) levels exceeded the legislative standards in all cities during the entire period. PM(2.5) pollution was related to COVID-19 incidence. The PM(2.5) levels and sampling rate were strong predictors of COVID-19 incidence during the pre-lockdown period. The PM(2.5) levels, population’s age, and density strongly predicted COVID-19 incidence during lockdown. Conclusions: Italy serves as a noteworthy paradigm illustrating that PM(2.5) pollution impacts COVID-19 spread. Even in lockdown, PM(2.5) levels negatively impacted COVID-19 incidence.