Assessment of the COVID-19 Lockdown Effects on Spectral Aerosol Scattering and Absorption Properties in Athens, Greece

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.

Characteristics and Source Apportionment of Black Carbon (BC) in a Suburban Area of Klang Valley, Malaysia

“…The AAE during MCO is higher, on average, by about 0.04-0.05. This finding is in line with recent studies on the impact of Athens lockdown on carbonaceous particle concentrations [59]. Interestingly, the difference in AAE during MCO compared with before MCO is least on Sunday.…”

Assessment of potential benefits of traffic and urban mobility reductions during COVID-19 lockdowns: dose-response calculations for material corrosions on built cultural heritage

“…The reduction in gas consumption and sharp reduction in international and domestic air traffic have also an important role in the reduction of the SO 2 levels around the world (Biswas et al 2020 ; Filonchyk and Peterson 2020 ; Pei et al 2021 ). Regarding O 3 , as a secondary pollutant, due to the NOx-sensitive regime, the observed reduction in NOx emissions would cause an increase in O 3 levels under a potential VOC-sensitive regime (Tables 3 – 4 and Figure 4 ) (Broomandi et al 2020 ; Casado-Aranda et al 2021 ; Kaskaoutis et al 2021 ; Kerimray et al 2020 ; Kumari and Toshniwal 2020 ; Lian et al 2020 ; Lokhandwala and Gautam 2020 ).…”

Impact of COVID-19 induced lockdown on land surface temperature, aerosol, and urban heat in Europe and North America

“…Lower levels of emissions, including the reduced concentrations of the light-absorbing OC and BC ( Ramanathan & Carmichael, 2008 ; Tiwari et al, 2016 ), might have significantly altered the radiative forcing and consequently changed the LSTs. Some studies have also demonstrated decreased aerosol radiative forcing values (–24.3 W m −2 at surface and –16 W m −2 at TOA in the short wave) due to lower AODs during the lockdown period in Madrid ( Barragan et al, 2020 ) and considerable decreases in carbonaceous aerosol (BC and Brown Carbon) absorption in Wuhan ( Wang et al, 2021 ) and Athens ( Kaskaoutis et al, 2021 ). In addition, a decrease in the radiative forcing in East Asia was attributed to reductions in AOD, with one‐third of the reduced anomalies to be attributed to the lockdown, while the remaining was attributed to natural factors, such as meteorological variability and surface heterogeneity ( Ming et al, 2021 ).…”

“…During the COVID-19 lockdowns, satellite-derived AOD data revealed that the aerosol levels reduced substantially by 40–60% across urban areas in south and southeast Asia ( Kanniah et al, 2020 ; Pathakoti et al, 2021 ; Ranjan et al, 2020 ). Recent works also revealed a large reduction in BC levels, as well as significant modulations in aerosol scattering and absorption properties enabling to modify the radiation budget and temperature at the surface and in the lower atmosphere ( Anil & Alagha, 2020 ; Kaskaoutis et al, 2021 ; Wang et al, 2021 ).…”