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\xa0Delhi, 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\xa0COVID-19 lockdown\xa0emission 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\xa0lockdown phase 1; thus, this period was used to report the\xa0COVID-19 baseline threshold values\xa0(CBT; threshold value is the upper limit of baseline variation). Of the various\xa0statistical methods used median\u2009+\u20092 median absolute deviation (mMAD)\xa0was most suitable, indicating CBT values\xa0of 143 and 75 ug/m 3 for PM 10 and PM 2.5 , respectively. This results although preliminary, but\xa0it\xa0gives 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\xa0as a first line of information\xa0to set future\xa0target limits\xa0or to\xa0develop effiective management policies for achieving better air quality in urban centres like Delhi.