Abstract
The combined use of Lecce-University AERONET-photometer measurements and PM2.5, PM10, NO2, CO, and SO2 concentrations from different sites of Apulia-Region Air-Quality Agency represents the peculiarity of this study, which evaluates the impact of COVID-19 lockdown (LD) measures on aerosol and gaseous pollutants. Monthly-averaged columnar and surface parameters of the 2020-year were compared with corresponding monthly parameters of the ref-year obtained by averaging 2017, 2018, and 2019 measurements in order to evaluate LD measure impacts by Average Percent Departure (APD%). Photometer measurements showed that LD measures were likely responsible for the decrease in Aerosol Optical Depth (AOD). The APD% estimated between the 2020- and ref-year AOD (at 440 nm) was characterized by negative values from June to August, reaching the smallest mean value (−46%) in June. Moreover, the columnar aerosol load appeared less affected by continental urban/industrial particles than previous years in the summer of 2020. The PM-concentration-APD% calculated at ten sites was characterized by monthly trends similar to those of AOD-APD%. PM-APD% values varied from site to site and smaller values (up to −57% in June) were on average detected at urban/suburban sites than at background sites (up to −37%). The impact of LD measures on gaseous pollutants was observed from the onset of LD.
Highlights
The whole 2020-year measurements of the selected air pollution parameters have been compared with the corresponding ones of a ref-year, based on the 2017, 2018, and 2019 measurements, to better identify/quantify the duration of the LD measure impact on pollutants
The comparison of the COVID19-LD effects on ground-level air pollutant properties, mostly affected by local meteorology and pollution sources, with those on the columnar aerosol particles, which are instead mostly affected by long-range transboundary air pollution, represents one of the main novel contributions of this study
Sun/sky photometer measurements have highlighted a significant decrease in the columnar aerosol load and a change of the mean particle size/type
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Another review of the lockdown impacts on the air quality has been provided by Skiriene and Stasiskiene [19]; they have estimated that the reduction in NO2 , PM2.5, and PM10 was approximately in the range of 20–40%, analysing data from 5 different European countries (England, Italy, Spain, France, and Sweden). Munir et al [20] compared three different approaches to assess their performance, using both estimated and measured air quality and meteorology data from several air quality monitoring stations in Reading (England) They found that changes in pollutant concentrations varied both in space and in time according to the adopted approach, the type of monitoring site and the data type. The analysis of the LD measure impacts on pollution at different sites deserves attention; most of the previous studies focused on the LD impacts up to April and/or May 2020
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