Long-Term COVID-19 Restrictions in Italy to Assess the Role of Seasonal Meteorological Conditions and Pollutant Emissions on Urban Air Quality

A year-round air quality analysis was addressed over four Italian cities (Milan, Turin, Bologna, and Florence) following the outbreak of the Coronavirus 2019 (COVID-19) pandemic. NO2, O3, PM2.5, and PM10 daily observations were compared with estimations of meteorological variables and observations of anthropogenic emission drivers as road traffic and heating systems. Three periods in 2020 were analysed: (i) the first (winter/spring) lockdown, (ii) the (spring/summer) partial relaxation period, and (iii) the second (autumn/winter) lockdown. During the first lockdown, only NO2 concentrations decreased systematically (and significantly, between -41.9 and -53.9%), mainly due to the drastic traffic reduction (-70 to -74%); PM2.5 varied between -21 and +18%, PM10 varied between -23 and +9%, and O3 increased (up to +17%). During the partly relaxation period, no air quality issues were observed. The second lockdown was particularly critical as, although road traffic significantly reduced (-30 to -44%), PM2.5 and PM10 concentrations dramatically increased (up to +87 and +123%, respectively), mostly due to remarkably unfavourable weather conditions. The latter was confirmed as the main driver of PM's most critical concentrations, while strong limitations to anthropogenic activity--including traffic bans--have little effect when taken alone, even when applied for more than two months and involving a whole country.