Spatial and temporal variations of the PM<subscript>2.5</subscript> concentrations in Hanoi metropolitan area, Vietnam, during the COVID-19 lockdown.

The Vietnamese government has issued several directives of lockdown in Hanoi, the capital city, for a month (1–30 April 2020) to prevent the human-to-human transmission of COVID-19. This action has affected air pollution due to a decline in transportation. Therefore, this study investigates spatial and temporal change in the PM 2.5 concentrations during the first 4 months of 2020 in Hanoi metropolitan area. Spatial distribution maps of the PM 2.5 concentration in Hanoi were provided for the first time. The average PM 2.5 concentrations at the 22 air monitoring stations were strongly correlated with the population. April had a significantly lower level of PM 2.5 than the other 3 months. In particular, the concentrations of PM 2.5 and NO 2 decreased by 12 and 54%, respectively, between March and April, especially at areas for commercial activities. In April, a higher level of PM 2.5 was recorded between Tuesday–Thursday, which is a reverse trend with that in March. Furthermore, Monday and Friday did not show rush hour peaks for the PM 2.5 levels in April. A decrease in the PM 2.5 concentrations was partly influenced by the long-range transport from the outside to Hanoi. This study implies that a reduction in traffic volumes and public activities may possibly improve the air quality. [ABSTRACT FROM AUTHOR]

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