2020 COVID-19 lockdown and the impacts on air quality with emphasis on urban, suburban and rural zones.

Air quality improvements pollution changes due to COVID-19 restrictions have been reported for many urban developments and large metropolitan areas, but the respective impacts at rural and remote zones are less frequently analysed. This study evaluated air pollution changes across all Portugal (68 stations) considering all urban, suburban and rural zones. PM10, PM2.5, NO2, SO2, ozone was analysed in pre-, during, and post-lockdown period (January-May 2020) and for a comparison also in 2019. NO2 was the most reduced pollutant in 2020, which coincided with decreased traffic. Significant drop (15-71%) of traffic related NO2 was observed specifically during lockdown period, being 55% for the largest and most populated region in country. PM was affected to a lesser degree (with substantial differences found for largely populated areas (Lisbon region ~ 30%; North region, up to 49%); during lockdown traffic-related PM dropped 10-70%. PM10 daily limit was exceeded 50% less in 2020, with 80% of exceedances before lockdown period. SO2 decreased by 35%, due to suspended industrial productions, whereas ozone concentrations slightly (though not significantly) increased (83 vs. 80 µg m-3).