Co-effects of COVID-19 and Meteorology on PM2.5 Decrease in Ho Chi Minh City, Vietnam: A Comparison of 2016-2019 and 2020-2021

The coronavirus disease 2019 (COVID-19) measures during 2020-2021 may lead to a downward trend of fine particulate matter (PM2.5) concentrations in Ho Chi Minh City (HCMC), which is one of the most air-polluted cities in Vietnam. This study aimed to compare PM2.5 variations during the COVID-19 period (2020-2021) with a short-term trend of PM2.5 (2016-2019) in HCMC in conjunction with meteorological conditions. Five fixed-site locations were chosen to monitor PM2.5 concentrations by using low-cost particulate matter sensors (Purple Air II-SD) in five urban districts of HCMC from December 2019 to March 2021. This study also collected hourly PM2.5 concentrations from the United States Consulate General HCMC and meteorological variables (i.e., wind speed, wind direction, air temperature, and relative humidity) from the weather station at Tan Son Nhat International Airport, 2016-2021. PM2.5 concentrations of the COVID-19 period in HCMC were notably less than those of the 2016-2019 period by 18%. However, about half of the days during this period still had daily PM2.5 concentrations exceeding the World Health Organization's standard of 15 mu g m-3. Besides the impacts of COVID-19 restrictions on the PM2.5 decrease, noticeable co-effects of meteorological variables on the decline of PM2.5 in HCMC were also observed in the rainy season and with the west-south-west monsoon wind direction. Wind speed and air temperature substantially contributed to PM2.5 reductions in Bayesian multiple linear regression models. In conclusion, the large decrease of PM2.5 concentrations during the unprecedented period of COVID-19 pandemic gave us a better chance to more fully comprehend the PM2.5 pollution status in HCMC for future reference.