Statistical Analysis for Understanding PM<subscript>2.5</subscript> Air Quality and the Impacts of COVID-19 Social Distancing in Several Provinces and Cities in Vietnam.

Air pollution, especially in urban regions, is receiving increasing attention in Vietnam. Consequently, this work aimed to study and analyze the air quality in several provinces and cities in the country focusing on PM2.5. Moreover, the impacts of COVID-19 social distancing on the PM2.5 level were investigated. For this purpose, descriptive statistic, Box and Whisker plot, correlation matrix, temporal variation, and trend analysis were conducted. R-based program and the R package "openair" were employed for the calculations. Hourly PM2.5 data were obtained from 8 national air quality monitoring sites. The study results indicated that provinces and cities in the North experienced more PM2.5 pollution compared to the Central and South. PM2.5 concentrations at each monitoring site varied significantly. Among monitoring sites, the northern sites showed high PM2.5 correlations with each other than the other sites. Seasonal variation was observed with high PM2.5 concentration in the dry season and low PM2.5 concentration in the wet season. PM2.5 concentration variation during the week was not so different. Diurnal variation showed that PM2.5 concentration rose at peak traffic hours and dropped in the afternoon. There was mainly a decreasing trend in PM2.5 concentration over the studied period. The COVID-19 pandemic has contributed to PM2.5 reduction. In the months implemented social distancing for preventing the epidemic, PM2.5 concentration declined but it would mostly increase in the following months. This study provided updated and valuable assessments of recent PM2.5 air quality in Vietnam. [ABSTRACT FROM AUTHOR]