Emission reduction of black carbon and polycyclic aromatic hydrocarbons during COVID-19 pandemic lockdown

Abstract

The global pandemic COVID-19 necessitated various responses throughout the world, including social distancing, use of mask, and complete lockdown. While these measures helped prevent the community spread of the virus, the resulting environmental benefits of lockdown remained mostly unnoticed. While many studies documented improvements in air quality index, very few have explored the reduction in black carbon (BC) aerosols and polycyclic aromatic hydrocarbons (PAHs) concentrations due to lockdown. In this study, we evaluated the changes in concentrations of BC, PAHs, and PM_2.5 before and during the lockdown period. Our results show that lockdown resulted in a significant reduction in concentrations of these pollutants. The average mass concentration of BC, PAHs, and PM_2.5 before the lockdown was 11.71 ± 3.33 μgm^-3, 108.71 ± 27.77 ngm^-3, and 147.65 ± 41.77 μgm^-3, respectively. During the lockdown period, the concentration of BC, PAHs, and PM_2.5 was 2.46 ± 0.95 μgm^-3, 23.19 ± 11.21 ngm^-3, and 50.31 ± 11.95 μgm^-3, respectively. The diagnostic ratio analysis for source apportionment showed changes in the emission sources before and during the lockdown. The primary sources of PAHs emissions before the lockdown were biomass, coal combustion, and vehicular traffic, while during the lockdown, PAHs emissions were primarily from the combustion of biomass and coal. Similarly, before the lockdown, the BC mass concentrations came from fossil-fuel and wood-burning, while during the lockdown period, most of the BC mass concentration came from wood-burning. Human health risk assessment demonstrated a significant reduction in risk due to inhalation of PAHs and BC-contaminated air.

Keywords: Aethalometer; Backward trajectory; Black carbon; COVID-19; Emission sources; Health risk assessment; PAHs.

Fig. 1

Satellite aerial view (Google Earth) of the sampling area at National Institute Technology, Jamshedpur (NIT J)

Fig. 2

Time average map of BC surface mass concentration monthly 0.5 × 0.625 deg. [MERRA-2 Model M2TMNXAER v 5.12.4] at the two different situations. a Before the lockdown period. b During the lockdown period

Fig. 3

Daily basis mass concentration of PM_2.5 and BC before and during the lockdown period at NIT J

Fig. 4

Monthly basis mass concentration with standard deviation of PM_2.5 and BC before and during the lockdown period at NIT J

Fig. 5

Concentration (ng/m³) of PAHs before and during the lockdown periods at NIT J

Fig. 6

Seven-day air mass back-trajectories as well as fire count graph on two different situations. a Before the lockdown period. b During the lockdown period, at altitude level of 500 m above ground level, over sampling side

Fig. 7

Fractional contribution of BC measured at 370 and 880 nm before and during the lockdown period at NIT J