Abstract:Abstract. To mitigate the impacts of the pandemic of coronavirus disease 2019 (COVID-19), the Indian government implemented lockdown measures on March 24, 2020, which prohibit unnecessary anthropogenic activities and thus leading to a significant reduction in emissions. To investigate the impacts of this lockdown measures on air quality in India, we used the Community Multi-Scale Air Quality (CMAQ) model to estimate the changes of key air pollutants. From pre-lockdown to lockdown periods, improved air quality … Show more
“…Overall, N AIT reduced by approximately 85% during LCD, implying reduced primary anthropogenic emissions or secondary formation or both. The time evolution of number concentrations of N TOT also showed similar reductions (86%) during LCD (Figure 4b), indicating that the air quality was significantly improved due to the primary emission reduction during LCD (Srivastava et al., 2021; Zhang et al., 2021).…”
To control the spread of the novel 2019 Coronavirus (COVID‐19), the Government of India enforced nationwide social and transportation restrictions (lockdown) in three phases from the evening of 24 March to 31 May 2020, which resulted in a significant reduction of primary emissions. Here, we performed the analyses of particle number size distribution measurements in the particle size range of 1.2–3 nm and 10–514 nm carried out from 15 April to 31 May 2020 (lockdown, LCD) and compared with measurements from the previous year during the same time period (15 April to 31 May 2019, business‐as‐usual, BAU) at University of Hyderabad in Hyderabad, India. The number concentrations of sub‐3 nm particles were comparable between LCD and BAU, but the number concentrations of particles greater than 10 nm diameter were lower by about 85% during LCD than BAU. It indicates that the reduction in primary anthropogenic emissions did not inhibit the formation of sub‐3 nm particles. But the frequency of occurrence of the new particle formation and growth (NPF&G) events was three‐fold lower during LCD than BAU. The ratio of formaldehyde to nitrogen dioxide indicated that India falls in a NOx‐limited regime, which reduces ambient ozone concentrations (lower condensable vapors via ozone oxidation of volatile organic compounds). Besides, the lower temperature (lower hydroxyl radical concentration) and lower wind speed during LCD may have contributed to the suppression of NPF&G events. Therefore, we emphasize the need to account for processes and interactions related to NPF&G in formulating particulate pollution mitigation policies in urban environments.
“…Overall, N AIT reduced by approximately 85% during LCD, implying reduced primary anthropogenic emissions or secondary formation or both. The time evolution of number concentrations of N TOT also showed similar reductions (86%) during LCD (Figure 4b), indicating that the air quality was significantly improved due to the primary emission reduction during LCD (Srivastava et al., 2021; Zhang et al., 2021).…”
To control the spread of the novel 2019 Coronavirus (COVID‐19), the Government of India enforced nationwide social and transportation restrictions (lockdown) in three phases from the evening of 24 March to 31 May 2020, which resulted in a significant reduction of primary emissions. Here, we performed the analyses of particle number size distribution measurements in the particle size range of 1.2–3 nm and 10–514 nm carried out from 15 April to 31 May 2020 (lockdown, LCD) and compared with measurements from the previous year during the same time period (15 April to 31 May 2019, business‐as‐usual, BAU) at University of Hyderabad in Hyderabad, India. The number concentrations of sub‐3 nm particles were comparable between LCD and BAU, but the number concentrations of particles greater than 10 nm diameter were lower by about 85% during LCD than BAU. It indicates that the reduction in primary anthropogenic emissions did not inhibit the formation of sub‐3 nm particles. But the frequency of occurrence of the new particle formation and growth (NPF&G) events was three‐fold lower during LCD than BAU. The ratio of formaldehyde to nitrogen dioxide indicated that India falls in a NOx‐limited regime, which reduces ambient ozone concentrations (lower condensable vapors via ozone oxidation of volatile organic compounds). Besides, the lower temperature (lower hydroxyl radical concentration) and lower wind speed during LCD may have contributed to the suppression of NPF&G events. Therefore, we emphasize the need to account for processes and interactions related to NPF&G in formulating particulate pollution mitigation policies in urban environments.
“…For instance, the pandemic restrictions in most of the European countries occurs in parallel with exceptionally blue skies and new extremes in surface irradiance ( van Heerwaarden et al, 2021 ). Improved air quality associated with COVID-19 lockdowns were also documented for India ( Srivastava et al, 2021 , Zhang et al, 2021 ), Iran ( Broomandi et al, 2020 ), and the United States ( Berman and Ebisu, 2020 ). Fig.…”
The pandemic in 2020 caused an abrupt change in the emission of anthropogenic aerosols and their precursors. We estimate the associated change in the aerosol radiative forcing at the top of the atmosphere and the surface. To that end, we perform new simulations with the CMIP6 global climate model EC-Earth3. The simulations use the here newly created data for the anthropogenic aerosol optical properties and an associated effect on clouds from the simple plumes parameterization (MACv2-SP), based on revised SO
2
and NH
3
emission scenarios. Our results highlight the small impact of the pandemic on the global aerosol radiative forcing in 2020 compared to the CMIP6 scenario SSP2-4.5 of the order of +0.04 Wm
−2
, which is small compared to the natural year-to-year variability in the radiation budget. Natural variability also limits the ability to detect a meaningful regional difference in the anthropogenic aerosol radiative effects. We identify the best chances to find a significant change in radiation at the surface during cloud-free conditions for regions that were strongly polluted in the past years. The post-pandemic recovery scenarios indicate a spread in the aerosol forcing of −0.68 to −0.38 Wm
−2
for 2050 relative to the pre-industrial, which translates to a difference of +0.05 to −0.25 Wm
−2
compared to the 2050 baseline from SSP2-4.5. This spread falls within the present-day uncertainty in aerosol radiative forcing and the CMIP6 spread in aerosol forcing at the end of the 21st century. We release the new MACv2-SP data for studies on the climate response to the pandemic and the recovery scenarios. Our 2050 forcing estimates suggest that sustained aerosol emission reductions during the post-pandemic recovery cause a stronger climate response than in 2020, i.e., there is a delayed influence of the pandemic on climate.
“…In addition to major urban agglomerations, the study on Hat Yai, Thailand, indicated that small cities also saw air quality improvements during the lockdown period ( Stratoulias and Nuthammachot, 2020 ). As a heavily polluted country, India experienced unprecedented air pollutant emission decline during the pandemic ( Das et al, 2021 ; Sharma et al, 2020 ; Zhang et al, 2021 ).…”
Previous studies have evaluated the impact of lockdown measures on air quality during the COVID-19 pandemic in China, but few have focused on the temporal characteristics and spatial heterogeneity of the impact across all 337 prefecture cities. In this study, we estimated the impact of the lockdown measures on air quality in each of 337 cities using the Regression Discontinuity in Time method. There was a short-term influence from January 24
th
to March 31
th
in 2020. The 337 cities could be divided into six categories showing different response and resilience patterns to the epidemic. Fine particulate matter (PM
2.5
) in 89.5% of the cities was sensitive to the lockdown measures. The change of air pollutants showed high spatial heterogeneity. The provinces with a greater than 20% reduction in PM
2.5
and PM
10
and greater than 40% reduction in NO
2
during the impact period were mainly concentrated southeast of the “Hu Line”. Compared to the no-pandemic scenario, the national annual average concentration of PM
2.5
, NO
2
, PM
10
, SO
2
, and CO in 2020 were decreased by 6.3%, 10.6%, 7.4%, 9.0%, and 12.5%, respectively, while that of O
3
increased by 1.1%.This result indicates that 2020 can still be used as a baseline for setting and allocating air improvement targets for the next five years.
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