Abstract
The COVID-19 pandemic altered the human mobility and economic activities immensely, as authorities enforced unprecedented lock down regulations. In order to reduce the spread of COVID-19, a complete lockdown was observed between 24 March - 31 May 2020 in Pakistan. This paper aims at investigating the PM(2.5), AOD and column amounts of six trace gases (NO(2), SO(2), CH(4), HCHO, C(2)H(2)O(2), and O(3)) by comparing periods of reduced emissions during lockdown periods with reference periods without emission reductions over Lahore, Pakistan. HYSPLIT cluster trajectory analyses were performed, which confirmed similar meteorological flow conditions during lockdown and reference periods. This provides confidence that any change in air quality conditions would be due to changes in human activities and associated emissions. The results show about 38% reduction in ambient surface PM(2.5) levels during the lockdown period. This change also positively correlated with MODIS(DB) and AERONET(AOD) data with a decrease of AOD by 42% and 35%, respectively. Reductions for tropospheric columns of NO(2) and SO(2) were about 20% and 50%, respectively during a semi lockdown period, while no reduction in the CH(4,) C(2)H(2)O(2), HCHO and O(3) levels occurred. During the lockdown period NO(2,) O(3) and CH(4) were about 50%, 45% and 25% lower, respectively, but no reduction in SO(2), C(2)H(2)O(2) and HCHO levels were noticed compared to the reference lockdown period for Lahore. HYSPLIT cluster trajectory analysis revealed the greatest impact on Lahore air quality through local emissions and regional transport from the east (agricultural burning and industry).