Different approaches to explore the impact of COVID-19 lockdowns on carbonaceous aerosols at a European rural background site

To prevent the fast spread of COVID-19, worldwide restrictions have been put in place, leading to a reduction in emis-sions from most anthropogenic sources. In this study, the impact of COVID-19 lockdowns on elemental (EC) and or-ganic (OC) carbon was explored at a European rural background site combining different approaches: - Horizontal approach (HA) consists of comparing concentrations of pollutants measured at 4 m a.g.l. during pre-COVID period (2017-2019) to those measured during COVID period (2020-2021); - Vertical approach (VA) con-sists of inspecting the relationship between OC and EC measured at 4 m and those on top (230 m) of a 250 m-tall tower in Czech Republic. The HA showed that the lockdowns did not systematically result in lower concentrations of both carbonaceous fractions unlike NO2 (25 to 36 % lower) and SO2 (10 to 45 % lower). EC was generally lower during the lockdowns (up to 35 %), likely attributed to the traffic restrictions whereas increased OC (up to 50 %) could be attributed to enhanced emissions from the domestic heating and biomass burning during this stay-home pe-riod, but also to the enhanced concentration of SOC (up to 98 %). EC and OC were generally higher at 4 m suggesting a greater influence of local sources near the surface. Interestingly, the VA revealed a significantly enhanced correlation between EC and OC measured at 4 m and those at 230 m (R values up to 0.88 and 0.70 during lockdown 1 and 2, re-spectively), suggesting a stronger influence of aged and long distance transported aerosols during the lockdowns. This study reveals that lockdowns did not necessarily affect aerosol absolute concentrations but it certainly influenced their vertical distribution. Therefore, analyzing the vertical distribution can allow a better characterization of aerosol prop-erties and sources at rural background sites, especially during a period of significantly reduced human activities.

Automated summary

To prevent the fast spread of COVID-19, restrictions were implemented worldwide, which resulted in reduced emissions from most sources. This study investigated the impact of COVID-19 lockdowns on elemental and organic carbon at a rural background site in Europe using horizontal and vertical approaches. The findings showed that the lockdowns did not consistently lead to lower concentrations of carbonaceous fractions, but had different effects on EC and OC. EC was generally lower due to traffic restrictions, while OC increased possibly due to enhanced emissions from domestic heating and biomass burning. The vertical approach revealed a stronger influence of aged and long-distance transported aerosols during the lockdowns. This study highlights the importance of analyzing the vertical distribution of aerosols to better understand their characteristics and sources during periods of reduced human activities.