A wide-ranging investigation of the COVID-19 lockdown effects on the atmospheric composition in various Italian urban sites (AER - LOCUS)

A widE-Ranging investigation of the first COVID-19 LOCkdown effects on the atmospheric composition in five Italian Urban Sites (AER-LOCUS) has been carried out and is presented in this study. The analysis uses particle and gas concentrations from surface in situ sampling, column aerosol and gas properties from photometer/spectrometers, and satellite NO2 determinations at five sites distributed over the whole Italian territory: Aosta, Milan, Bologna, Rome, and Taranto. These data are related to meteorological conditions to identify the numerous events of long-range transport and separate local from remote influences. Four different types of long-range transport over Italy are identified during the lockdown period, affecting PM10, PM2.5, and NO2 concentrations, and aerosol optical depths: fires plumes from Eastern Europe and Montenegro, dust from the Caspian area and from the Sahara, and pollution from the Po Valley. Once the long-range transport events are identified and excluded, the variation of gas and particle concentrations occurring during the containment period is calculated with respect to the period 2015-2019. A general decrease of PM10 (ranging from a maximum of 52% in Aosta to a minimum of 4% in Taranto), PM2.5 (from 46% in Aosta and Milan to 0.6% in Bologna), BC (from 77% in Aosta to 25% in Milan), NO2 (from 72% in Rome to 4% in Taranto), and benzene (about 50%) concentration is found. A positive variation of PM2.5 is conversely found during March in the southern sites due to some stagnation events, and a strong increase of benzene (up to +104%) in the industrial area of Taranto. Ozone is found to increase by an average of about 30% in all sites. The removal of the long-range transport contributions affects the variations with respect to the reference period reducing the concentrations by up to 22% for PM10 and 29% for PM2.5 in the northern sites, and 18% for PM10 and 16% for PM2.5 in the southern sites. For NO2 the reduction due to the removal is up to 14% in Milan and 6% in the southern sites, while for the aerosol optical depth it is up to 70% in Aosta and 50% in Rome.