Drivers of air pollution variability during second wave of COVID-19 in Delhi, India

Abstract

To curb the 2nd wave of COVID-19 disease in April–May 2021, a night curfew followed by full lockdown was imposed over the National Capital Territory, Delhi. We have analyzed the observed variation in pollutants and meteorology, and role of local and transboundary emission sources during night-curfew and lockdown, as compared to pre-lockdown period and identical periods of 2020 lockdown as well as of 2018 and 2019. In 2021, concentration of pollutants (except O₃, SO₂, and toluene) declined by 4–16% during night-curfew as compared to the pre-lockdown period but these changes are not statistically significant. During lockdown in 2021, various pollutants decreased by 1–28% as compared to the night-curfew (except O₃ and PM₂.₅), but increased by 31–129% compared to the identical period of 2020 lockdown except O₃. Advection of pollutants from the region of moderate lockdown restrictions and an abrupt increase in crop-residue burning activity (120–587%) over Haryana and Punjab increased the air pollution levels over NCT during the lockdown period of 2021 as compared to 2020 in addition to a significant contribution of long-range transport. The increase in PM₂.₅ during the lockdown period of 2021 compared to 2020 might led to 5–29 additional premature mortalities.

NASA Satellite Measurements Show Global‐Scale Reductions in Free Tropospheric Ozone in 2020 and Again in 2021 During COVID‐19

“…Saharan et al. ( 2022 ) shows higher measured surface pollutants in 2021 in Delhi, India compared to 2020, but still less than pre‐COVID; their Table 2 for both March and April shows reductions in CO, O 3 , and NO x during 2021 relative to years 2018 and 2019. Sarmadi et al.…”

“…The general consensus is that global pollution was greater in 2021 compared to 2020, but still lower than in years prior to COVID-19. Saharan et al (2022) shows higher measured surface pollutants in 2021 in Delhi, India compared to 2020, but still less than pre-COVID; their This paper provides a global evaluation of reductions in free tropospheric ozone in years 2020 and 2021 during the COVID-19 pandemic using ozone measurements from combined EPIC, OMPS, OMI, and Microwave Limb Sounder (MLS) satellite instruments. A primary motivation is to show that there were large planetary-scale decreases of NH tropospheric ozone in year 2021 that were similar to the decreases in year 2020.…”

Spatio-temporal variation in air quality and unexpected pollution levels during the lamp event over the Indo-Gangetic Plain in the first wave of the COVID-19 pandemic

“…However, the trend of benzene was similar to PBLH which is common in urban regions. 48 After the event, around 21:30 h, within 20 min, it was observed that the PM 2.5 levels rose suddenly from 66 μg m −3 to 95–100 μg m −3 (Fig. 4), whereas the concentration of PM 2.5 at night generally ranged between 40 and 55 μg m −3 during P1 of the lockdown (Fig.…”

“…However, the trend of benzene was similar to PBLH which is common in urban region. 48 After the event, around 21:30 h, within 20 min, it was observed that the PM 2.5 levels rose suddenly from 66 µg/m 3 to 95-100 µg/m 3 (Figure 4), whereas the concentration of PM 2.5 at night generally ranged between 40-55 µg/m 3 during P1 of the lockdown (Figure 3 (upper panel)). Additionally, the concentration of benzene showed a similar diurnal pattern as PM 2.5 with concentration 2.3 ± 0.6 µg/m 3 during the day and 2.5 ± 0.4 µg/m 3 during the night in the course of P1 of the lockdown, while, on April 5, 2020 following the Lamp event, the night levels of benzene rose to 3.9 µg/m 3 , indicating the additional source of pollutants in the same environment.…”

“…The high loadings of PM 2.5 and benzene were observed at all monitoring sites in PC1, along with the site-specific loadings of NO 2 , CO and toluene, which represent emissions from fossil fuel combustion of vehicles, industries, and the oil-based emissions. 48 Moreover, the higher loadings of PM₂.₅ and benzene reflects a larger contribution from the emissions of oil-lamps or candles in the vicinity of the monitoring sites rather than vehicles or industries whereas sitespecific loadings of NO 2 , CO and toluene could be associated to limited vehicular activity (mostly for grocery and pharmacy) or diffused coal burning that was not uniform during lockdown (SI Figure 1). This is further supported by the strong correlations observed between PM 2.5 -benzene (0.8), PM 2.5 -CO (0.7), toluene -benzene (0.5) and toluene -CO (0.5).…”