In 2020, the Monte Cimone global station has registered the lowest tropospheric ozone values since 1996: this was probably caused by the pollutant emissions reductions due to COVID-19 lockdowns. The results of a study published on Environmental Research Letters
Several studies in 2020 analyzed ozone (O3) variability in the troposphere as a function of the restriction measures related to the containment of the spread of the COVID-19. Most of these studies were conducted mainly in urban or industrial agglomerates. While the O3 plays a beneficial role in the stratosphere, by absorbing UV radiations emitted from the Sun, in the troposphere (i.e., between the ground level and 12–15 km) O3 is a secondary pollutant, with adverse effects on population health and ecosystems. In addition, it acts as a regional greenhouse gas with negative impacts on climate.
A study led by National Research Council of Italy – Institute of Atmospheric Sciences and Climate (Cnr-Isac), in collaboration with the University of Urbino, the National Research Council of Italy – Institute of Marine Sciences (Cnr-Ismar), and Eidgenössische Technische Hochschule (Eth) Zurich, analyzed, for the first time in Italy, such potential impacts on O3 concentrations measured at a remote high-altitude site, outside the Planetary Boundary Layer (PBL), i.e., the tropospheric layer directly influenced by the Earth’s surface and where air- and climate-altering pollutants are directly emitted.
The team analyzed continuous measurements at the “O. Vittori” observatory, managed by Cnr-Isac in collaboration with the Italian Air Force (Camm Monte Cimone) and part of the WMO/GAW global station of Monte Cimone. The observatory is placed at the highest peak in the Italian Northern Apennines (44°12' N, 10°42' E, 2165 m), and it is located above the PBL for most of the year. During spring and summer 2020, low O3 values, with respect to the previous years, were observed at the station (figure 1). The analysis of meteorological variables and diel O3 cycles did not suggest mayor changes in the vertical transport of air masses at Monte Cimone related to the thermal circulation system.
The low O3 values that characterized spring and summer 2020 cannot be explained by differences in the large-scale scale circulation with respect to the previous five years. The periods with the lowest O3 values measured at Monte Cimone were observed together with air masses from the continental PBL. During spring and summer 2020, the COVID-19 restrictions reduced the anthropogenic emissions in the PBL of O3 precursors, i.e., those substances that, in the presence of solar radiation, favor O3 formation, and they can be emitted by anthropogenic activities, such as vehicular traffic. This was likely to be reflected in a decrease of the O3 amount above the PBL and at remote locations over northern Italy, especially when PBL air masses (e.g., from the Po basin) were transported vertically.
This study suggests the importance, as already shown by international studies, of limiting anthropogenic precursor emissions for decreasing the O3 amount in the free troposphere, where it acts as a greenhouse gas.
Davide Putero, Cnr-Isac di Torino - Paolo Cristofanelli, Cnr-Isac di Bologna
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