atmosphere Article Air Quality in the Italian Northwestern Alps during Year 2020: Assessment of the COVID-19 «Lockdown Effect» from Multi-Technique Observations and Models Henri Diémoz 1,*,† , Tiziana Magri 1,†, Giordano Pession 1, Claudia Tarricone 1, Ivan Karl Friedrich Tombolato 1, Gabriele Fasano 1,2 and Manuela Zublena 1 1 Regional Environmental Protection Agency (ARPA) Valle d’Aosta, 11020 Saint-Christophe, Italy;
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[email protected] (M.Z.) 2 Department of Physics, Sapienza University of Rome, 00185 Rome, Italy * Correspondence:
[email protected]; Tel.: +39-165-278576 † These authors contributed equally to this work. Abstract: The effect of COVID-19 confinement regulations on air quality in the northwestern Alps is assessed here based on measurements at five valley sites in different environmental contexts. Surface concentrations of nitrogen oxides (NO and NO2), ozone (O3), particulate matter (PM2.5 and PM10), together with a thorough microphysical (size), chemical, and optical (light absorption) aerosol characterisation, complemented by observations along the vertical column are considered. Even in the relatively pristine environment of the Alps, the «lockdown effect» is well discernible, both in the Citation: Diémoz, H.; Magri, T.; early confinement phase and in late 2020. The variations observed during the first confinement period Pession, G.; Tarricone, C.; Tombolato, in the city of Aosta (−61% NO, −43% NO2, +5% O3, +9% PM2.5, −12% PM10, relative to average I.K.F.; Fasano, G.; Zublena, M.