Abstract
COVID-19 is evolving into one of the worst pandemics in recent history, claiming a death toll of over 1.5 million as of December 2020. In an attempt to limit the expansion of the pandemic in its initial phase, nearly all countries imposed restriction measures, which resulted in an unprecedented reduction of air pollution. This study aims to assess the impact of the lockdown effects due to COVID-19 on in situ measured aerosol properties, namely spectral-scattering (bsca) and absorption (babs) coefficients, black carbon (BC) concentrations, single-scattering albedo (SSA), scattering and absorption Ångström exponents (SAE, AAE) in Athens, Greece. Moreover, a comparison is performed with the regional background site of Finokalia, Crete, for a better assessment of the urban impact on observed differences. The study examines pre-lockdown (1–22 March 2020), lockdown (23 March–3 May 2020) and post-lockdown (4–31 May 2020) periods, while the aerosol properties are also compared with a 3–4 year preceding period (2016/2017–2019). Comparison of meteorological parameters in Athens, between the lockdown period and respective days in previous years, showed only marginal variation, which is not deemed sufficient in order to justify the notable changes in aerosol concentrations and optical properties. The largest reduction during the lockdown period was observed for babs compared to the pre-lockdown (−39%) and to the same period in previous years (−36%). This was intensified during the morning traffic hours (−60%), reflecting the large decrease in vehicular emissions. Furthermore, AAE increased during the lockdown period due to reduced emissions from fossil-fuel combustion, while a smaller (−21%) decrease was observed for bsca along with slight increases (6%) in SAE and SSA values, indicating that scattering aerosol properties were less affected by the decrease in vehicular emissions, as they are more dependent on regional sources and atmospheric processing. Nighttime BC emissions related to residential wood-burning were slightly increased during the lockdown period, with respect to previous-year means. On the contrary, aerosol and pollution changes during the lockdown period at Finokalia were low and highly sensitive to natural sources and processes.
Highlights
The novel coronavirus SARS-COV-2 that was first evidenced in Wuhan, China, has evolved into the worst pandemic of the century so far due to widespread infection from late winter 2019 to this day [1,2]
Before focusing on the Athens urban environment, we examined the variability of bsca and black carbon (BC) components at the regional background site of Finokalia, Crete (Figure 2), in March–May 2020 with respect to previous years (2016–2019)
During the lockdown period, it can be seen in the graph that the bsca time-series was mostly within the shaded area corresponding to the standard deviation of the 2016–2019 mean
Summary
The novel coronavirus SARS-COV-2 that was first evidenced in Wuhan, China, has evolved into the worst pandemic of the century so far due to widespread infection from late winter 2019 to this day [1,2]. Numerous studies around the world, as in China and East Asia [13,14,15], India [16,17,18], Southeast Asia [19,20], Europe [21,22,23,24,25,26], North America [27,28] and South America [29,30], have analyzed the effect of COVID-19 lockdowns in spring 2020 on concentrations of particulate matter (PM) and gaseous pollutants (NOx, CO, O3, SO2, NH3, etc.) All these studies agree on an unprecedented reduction of air pollution worldwide due to drastic limitations in traffic and industrial activity [31,32,33]. Only a few works examined the changes in aerosol spectral absorption [43,44], while there is a lack of studies related to changes in spectral-scattering and single-scattering albedo (SSA)
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