Abstract
Abstract. The COVID-19 lockdown measures gradually implemented in Lombardy (northern Italy) from 23 February 2020 led to a downturn in several economic sectors with possible impacts on air quality. Several communications claimed in the first weeks of March 2020 that the mitigation in air pollution observed at that time was actually related to these lockdown measures without considering that seasonal variations in emissions and meteorology also influence air quality. To determine the specific impact of lockdown measures on air quality in northern Italy, we compared observations from the European Commission Atmospheric Observatory of Ispra (regional background) and from the regional environmental protection agency (ARPA) air monitoring stations in the Milan conurbation (urban background) with expected values for these observations using two different approaches. On the one hand, intensive aerosol variables determined from specific aerosol characterisation observations performed in Ispra were compared to their 3-year averages. On the other hand, ground-level measured concentrations of atmospheric pollutants (NO2, PM10, O3, NO, SO2) were compared to expected concentrations derived from the Copernicus Atmosphere Monitoring Service Regional (CAMS) ensemble model forecasts, which did not account for lockdown measures. From these comparisons, we show that NO2 concentrations decreased as a consequence of the lockdown by −30 % and −40 % on average at the urban and regional background sites, respectively. Unlike NO2, PM10 concentrations were not significantly affected by lockdown measures. This could be due to any decreases in PM10 (and PM10 precursors) emissions from traffic being compensated for by increases in emissions from domestic heating and/or from changes in the secondary aerosol formation regime resulting from the lockdown measures. The implementation of the lockdown measures also led to an increase in the highest O3 concentrations at both the urban and regional background sites resulting from reduced titration of O3 by NO. The relaxation of the lockdown measures beginning in May resulted in close-to-expected NO2 concentrations in the urban background and to significant increases in PM10 in comparison to expected concentrations at both regional and urban background sites.
Highlights
The COVID-19 pandemic is an epidemic of the coronavirus disease 2019 (COVID-19), of which the outbreak was first identified in Wuhan, China, in late December 2019
The observation and ENSEMBLE forecast data used to estimate the values expected for the air pollution variables discussed are described in Sects. 1 and 2 of the Supplement to this article
The absorption Ångström exponent (AÅE) values measured in 2020 can not be compared point to point to the 2017–2019 average in Fig. 5 because the use of wood fuel for domestic heating depends on weekend and cold-evening occurrences
Summary
The COVID-19 pandemic is an epidemic of the coronavirus disease 2019 (COVID-19), of which the outbreak was first identified in Wuhan, China, in late December 2019. The World Health Organization declared COVID-19 a pandemic on 11 March 2020. The first case of COVID-19 in northern Italy was detected on 20 February 2020 in Codogno, about 60 km south-east of Milan (Fig. 1). To reduce the virus spreading, the Italian government quickly adopted a series of measures, such as the quarantine for 10 municipalities, the cancellation of all main public events, and the closure of schools and universities in northern Italy (DL, 23 February 2020a). The lockdown started in all of Italy on 9 March 2020 (DPCM, 8 March 2020a).
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