Current Science

A. Ajay ¹, K. Krishna Moorthy ², S. K. Satheesh ³, G. Ilavazhagan ¹

Affiliations
1 Hindustan Institute of Technology and Science, Chennai 603 103, IN
2 Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru 560 012, IN
3 Divecha Centre for Climate Change, Indian Institute of Science, Bengaluru 560 012, IN

Abstract

Continuous analytical measurements of the loading and optical properties of near-surface aerosols over the megacity Bengaluru, in south India, are examined for the impact of the national lockdown (LD) associated with COVID-19 pandemic. The near total shutdown of rail, road, and air traffic as well as total closure of most of the business establishments and IT industry, especially during the first phase of the LD, is found to dramatically reduce black carbon (BC) abundance. Within one week of the first week of the LD phase 1 (LD1), the ambient BC concentration at the urban centre came down to levels comparable to those reported for remote rural locations, primarily due to >60% reduction in BC from fossil fuel (BCff) emissions. On the other hand, BC from biomass burning (BCwb) did not show any conspicuous impact. Consequently, the fraction of BCwb to BC more than doubled and the spectral absorption coefficient increased from ~1.15 to ~1.4. The single scattering albedo increased from its prevailing mean value 0.66 before LD to 0.74 during LD1 and then gradually decreased to 0.68 with increasing relaxations on vehicular traffic. The results reveal the unequivocal role of vehicular emissions in impacting the aerosol loading and their optical properties over Bengaluru. The study also shows how the environment responded to the gradual relaxations in the subsequent phases of LD. It is interesting to note that a few spells of strong rainfall towards the fourth phase of the LD impacted the aerosols non-selectively leading to sharp decrease in all the quantities. However, owing to the non-selective nature of the washout this large reduction in loading did not impact the single scattering albedo, unlike the case with the LD.

Keywords

Black Carbon, COVID-19 Lockdown, Scattering Coefficients, Single Scattering Albedo.

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A. Ajay ¹, K. Krishna Moorthy ², S. K. Satheesh ³, G. Ilavazhagan ¹

Affiliations
1 Hindustan Institute of Technology and Science, Chennai 603 103, IN
2 Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru 560 012, IN
3 Divecha Centre for Climate Change, Indian Institute of Science, Bengaluru 560 012, IN

Abstract

Long-term and continuous measurements of aerosol concentration and optical properties from the Challakere Climate Observatory, located in a remote rural semi-arid region northwest of Bengaluru, are examined for the impact of the prolonged and phased national lockdown during the COVID-19 pandemic. The analyses revealed that the lockdown, which almost brought all the anthropogenic activities (particularly associated with fossil fuel use such as in transport and industrial sectors) to a standstill and then slowly relaxed in phases, had very little impact on the aerosol properties at this remote site, in sharp contrast to the impacts seen in the major urban conglomerate, Bengaluru, located about 230 km southeast to Challakere. Rather than impacts from anthropogenic sources associated with fossil fuel combustion, the aerosol characteristics at Challakere are strongly influenced by regional and synoptic meteorology. The findings re-emphasize that the emissions from fossil fuel combustion in industrial and automobile sector are the major source of aerosols (especially absorbing type) over urban and semi-urban environments.

Keywords

Anthropogenic Emissions, Black Carbon, COVID-19 Lockdown, Rural Aerosols, Scattering Coefficients, Single Scattering Albedo.

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