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

Abstract

This study focuses on spatio-temporal variation in air quality caused by the nationwide lamp event of nine minutes named as the “#9 pm 9 min event” during the historic lockdown in the first wave of the COVID-19 pandemic across India in the year 2020. Due to the Janta curfew (March 22, 2020) and the lockdown (from March 25 to May 31, 2020), the concentration of pollutants like fine particulate matter (PM_2.5), trace gases such as nitrogen dioxide (NO₂), sulphur dioxide (SO₂), and carbon monoxide (CO), and volatile organic compounds (VOCs), namely benzene and toluene reduced significantly in the six most polluted cities, i.e., Agra, Ghaziabad, Lucknow, Meerut, Noida and Varanasi in the Indo-Gangetic Plain (IGP), while the concentration of ozone increased. A maximum decline in PM_2.5 concentrations was observed in Noida (43%), followed by Ghaziabad (39%), Lucknow (33%), Meerut (25%), Agra (23%) and Varanasi (5%) during phase-1 (P1) of lockdown in comparison with the period before lockdown. Similar to PM_2.5, other pollutants also decreased at all sites under consideration. This event (lamp event, #9 pm 9 min event) offered an exclusive opportunity to study the effects of burning oil lamps or candles in an open environment with minimum industrial and vehicular emissions. The decline in pollution levels reversed in the wake of the lamp event, which resulted in a sharp increase in pollutant concentrations, except for ozone levels. PM_2.5 mass concentrations were significantly correlated with benzene (0.7) and CO (0.7), whereas toluene was moderately correlated with benzene (0.5). Principal component analysis (PCA) also revealed that increases in the concentrations of PM_2.5, NO₂, CO, benzene and toluene were largely due to oil-based emissions. The study points out that future policy initiatives should take into account the changes in air quality which were seen during the lamp event. These changes have reinforced the necessity for comprehensive action across all emission sectors to achieve significant air quality improvements. It is also advised that people should strictly follow the guidelines issued by the government during such events.