Negative ozone anomalies at a high mountain site in northern Italy during 2020: a possible role of COVID-19 lockdowns?

Abstract

Several studies investigated the possible impacts of the restriction measures related to the containment of the spread of the COrona VIrus Disease (COVID-19) to atmospheric ozone (O _3 ) at global, regional, and local scales during 2020. O _3 is a secondary pollutant with adverse effects on population health and ecosystems and with negative impacts on climate, acting as greenhouse gas. Most of these studies focused on spring 2020 (i.e. March–May) and on observations in the planetary boundary layer (PBL), mostly in the vicinity of urban agglomerates. Here, we analyzed the variability of O _3 above the PBL of northern Italy in 2020 by using continuous observations carried out at a high mountain WMO/GAW global station in Italy (Mt. Cimone–CMN; 44°12′ N, 10°42′ E, 2165 m a.s.l.). Low O _3 monthly anomalies were observed during spring (MAM) and summer (JJA), when periods of low O _3 intertwined with periods with higher O _3 , within climatological ranges. A similar variability was observed for O _3 precursors like NO _2 and 15 anthropogenic non-methane volatile organic carbons, but the systematic O _3 anomalies were not reflected in these variables. The analysis of meteorological variables and diel O _3 cycles did not suggest major changes in the vertical transport related to the thermal circulation system in the mountain area. The analysis of five days back-trajectories suggested that the observed O _3 anomalies cannot be explained by differences in the synoptic-scale circulation with respect to the previous years alone. On the other hand, the characterization of two transport patterns (i.e. air masses from the regional PBL or from the free troposphere) and the analysis of back-trajectories suggested an important contribution of transport from the continental PBL during the periods with the lowest O _3 at CMN. When proxies of air mass transport from the regional PBL are considered, a lower NO _x content was pointed out with respect to the previous years, suggesting a lower O _3 production in a NO _x -limited atmosphere. Our study suggested for the first time that, during MAM and JJA 2020, the reduced anthropogenic emissions related to the COVID-19 restrictions lowered the amount of this short-lived climate forcer/pollutant at remote locations above the PBL over northern Italy. This work suggests the importance of limiting anthropogenic precursor emissions for decreasing the O _3 amount at remote locations and in upper atmospheric layers.

Keywords

• COVID-19
• ozone
• air mass transport
• mitigation
• Europe
• Po basin