Social restriction effects on air pollution: How the PM_2.5 concentration changed with lockdown management of COVID-19 pandemic control in Bangkok Thailand

Under rapid proceeding of COVID-19 pandemic, Thailand government announced lockdown and social restriction in March 2020. With the frustration of pandemic, anthropogenic etiology of air pollution was beneficially assessed on other hands. The study aims at exploring how PM2.5 concentration changed with lockdown management and social restriction as part of COVID-19 control in the Bangkok Metropolitan Region, Thailand. There was PM2.5 concentration reduction of roadside (18.6%) and ambient (9.2%) in COVID-19 lockdown period than the same months of previous consecutive year. Moreover, this study showed a clear decline of PM_2.5 during lockdown in both rush and non-rush hours except one roadside area which has a non-significant rising PM_2.5 because of trucks activities in some area. Additionally, the probable high concentration during the lockdowns period occurred at calm wind speed, mostly from the south direction, particularly in roadside area indicating the traffic source of PM_2.5 in the Conditional Bivariate Probability Function (CBPF) plot which estimate probable direction and source of air pollutant. Although PM_2.5 is significantly reduced in the lockdown period, it is still above 66% (33 microgram per cubic meter) of the Thailand standard in CBPF analysis. No specific minimum level of PM_2.5 is safe for health. However, it highlights monitoring emission sources and encouraging the community to make concerns about their daily contributing activities of air pollution.