COVID-19 lockdown: a rare opportunity to establish baseline pollution level of air pollutants in a megacity, India

Abstract

This paper analyses air quality data from megacity Delhi, India, during different periods related to the COVID-19, including pre-lockdown, lockdown and unlocked (post-lockdown) (2018–2020) to determine what baseline levels of air pollutants might be and the level of impact that could be anticipated under the COVID-19 lockdown emission scenario. The results show that air quality improved significantly during the lockdown phases, with the most significant changes occurring in the transportation and industrially dominated areas. A pronounced decline in PM 2.5 and PM 10 up to 63% and 58%, respectively, was observed during the lockdown compared to the pre-lockdown period in 2020. When compared to 2018 and 2019, they were lower by up to 51% and 61%, respectively, dropping by 56% during unlock. Some pollutants (NOx and CO) dropped significantly during lockdown, while SO 2 and O 3 declined only slightly. Moreover, when compared between the different phases of lockdown, the maximum decline for most of the pollutants and air quality index occurred during the lockdown phase 1; thus, this period was used to report the COVID-19 baseline threshold values (CBT; threshold value is the upper limit of baseline variation). Of the various statistical methods used median + 2 median absolute deviation (mMAD) was most suitable, indicating CBT values of 143 and 75 ug/m 3 for PM 10 and PM 2.5 , respectively. This results although preliminary, but it gives a positive indication that temporary lockdown can be considered as a boon to mitigate the damage we have done to the environment. Also, this baseline levels can be helpful as a first line of information to set future target limits or to develop effiective management policies for achieving better air quality in urban centres like Delhi. Supplementary Information The online version contains supplementary material available at 10.1007/s13762-021-03142-3.

Impact of COVID-19 Pandemic on Air Quality: A Systematic Review

“…As shown in Table 1 , decreases between 9–60%, 21.4–61.6%, and 30–66% were obtained for PM 2 . 5 , PM 10 , and NO 2 respectively (pollutants that were consistently reduced).The studies that also used satellite data corroborated the results obtained with the ground-based levels [ 33 , 57 , 88 , 89 , 90 ], and those that included AQI claimed that it improved during the lockdown period [ 54 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 ]. Besides, the higher levels of reduction were mainly found for the new industrialised areas, e.g., India and China [ 101 ].…”

Association of air pollution and meteorological variables with the two waves of COVID-19 pandemic in Delhi: A critical analysis

“…There was almost no change in the wind speed, which remained at 4 m s -1 during both waves. Sahoo et al (2021) also reported very minor variations in wind speed during the pre-and lockdown periods in Delhi. The maximum number of new COVID-19 cases per day during April 2020 was 356, which increased to 28395 during April 2021, indicating a faster spread of infection during the second wave ( Asrani et al, 2021 ).…”

Critical assessment of restrictive socioeconomic measures taken during the SARS-CoV-2 pandemic and their impact on air quality worldwide

“…Astana, which has an average weekly concentration of 61.25 μg m -3 , reduced its PM 2.5 concentration by 18% during the lockdown period (Rodríguez-Urrego and Rodríguez-Urrego, 2020). Delhi's PM 2.5 levels remained stable throughout India's lockdown period and up to July 2020 (Roy and Singha, 2021;Sahoo et al, 2021).…”