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 (O3) at global, regional, and local scales during 2020. O3 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 O3 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 O3 monthly anomalies were observed during spring (MAM) and summer (JJA), when periods of low O3 intertwined with periods with higher O3, within climatological ranges. A similar variability was observed for O3 precursors like NO2 and 15 anthropogenic non-methane volatile organic carbons, but the systematic O3 anomalies were not reflected in these variables. The analysis of meteorological variables and diel O3 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 O3 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 O3 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 O3 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 O3 amount at remote locations and in upper atmospheric layers.

Air Quality in the Italian Northwestern Alps during Year 2020: Assessment of the COVID-19 «Lockdown Effect» from Multi-Technique Observations and Models

“…Finally, it should be noticed that, in Donnas, the largest difference between the observed O 3 concentrations and the ones predicted by the random forest occurs in P5. This is consistent with the overall O 3 negative anomaly detected in northern Italy in summer 2020 [76], especially considering that Donnas is very close to the Po basin. The predictive statistical model provides similar results to the anomalies relative to the previous years, even enhancing the NO x reductions found in periods P2-P4.…”

“…In P2-P3, we observe an increase in Aosta-downtown compared to the random forest prediction and a decrease in P2 in Donnas. A possible reason for this contrasting behaviour could be that reduced titration by NO leads to increased concentrations of ozone in the urban environment of Aosta, while reduced precursors contribute to the decrease at the Donnas rural station, as also found at other remote Italian sites [76]. However, in contrast to P2-P3, O 3 concentrations slightly decrease in Aosta-downtown during the second lockdown in P6.…”

Understanding the environmental factors related to the decrease in Pediatric Emergency Department referrals for acute asthma during the SARS‐CoV‐2 pandemic

“…In densely populated areas, they clearly mimicked a reduction of traffic-related sources in concomitance with the restrictive measures, consistent with a mobility drop of 75%. 34 The abatement of traffic-related pollutants is in good agreement also with a recent study by Cristofanelli et al, 35 showing how during lockdowns reduced anthropogenic emissions modified air pollutant levels in Northern Italy, not only in the proximity of urban or industrial agglomerates but even in remote sites.…”

Variations of air pollutant response to COVID-19 lockdown in cities of the Tibetan Plateau

“…20 Meanwhile, diverse policies have been adopted by governments across the world, such as limiting public transportation, encouraging or mandating working from home, and enforcing closure of public services. 21,22 Global researchers focused on the air quality change due to lockdown from February to May in 2020, and mostly in the urban agglomerates: [23][24][25] The total gaseous oxidant (O x = NO 2 + O 3 ) showed limited change as gains in O 3 compensated for drops in NO 2 . Decreasing trends of PM 2.5 were observed in most cities, and short-term and unexpected uctuations were accounted for the atmospheric oxidation enhancement due to reduced titration.…”