Parichat Wetchayont 

With the outbreak of the COVID-19 pandemic around the world, many countries announced lockdown measures, including Thailand. Several scientific studies have reported on improvements in air quality due to the impact of these COVID-19 lockdowns. This study aims to investigate the effects of the COVID-19 lockdown and its driving influence factors on air pollution in Greater Bangkok, Thailand using in-situ measurements. Overall PM2.5, PM10, O3, and CO concentrations presented a significant decreasing trend during the COVID-19 outbreak year based on three periods: the before, lockdown and after periods, for PM2.5: 0.7%, 15.8% and 20.7%; PM10: 4.1%, 31.7% and 6.1%; O3: 0.3%, 7.1% and 4.7%, respectively, compared to the same periods in 2019. CO concentrations, especially, were increased by 14.7%, but decreased by 8.0% and 23.6% during the before, lockdown and after periods, respectively. Meanwhile, SO2 and NO2 increased by 54.0%, 41.5% and 84.6%, and 20.1%, 3.2% and 26.6%, respectively, during the before, lockdown and after periods. PCA analysis indicated a significant combination effect of atmospheric mechanisms that were strongly linked to emission sources such as traffic and biomass burning. It has been demonstrated that the COVID-19 lockdown can pause some of these anthropogenic emissions, i.e. traffic, commercial and industrial activities, but not all, even low traffic emissions can’t absolutely cause reductions in air pollution, since there are several primary emission sources that dominate the air quality over Greater Bangkok. Finally, these findings highlight the impact of the COVID-19 lockdown measures, not only on the air pollution levels, but also affects to air pollution characteristics, as well.