Air Quality Improvement during COVID-19 Lockdown in Bangkok Metropolitan, Thailand: Effect of the Long-range Transport of Air Pollutants

Wetchayont, P.; Hayasaka, T.; Khatri, P.

Lockdown measures have been adopted in many countries worldwide due to the onset of the COVID-19 pandemic, including in Thailand. Air quality improvements with regard to restrictions of daily movement among Bangkok people have been reported. This study explores the impact of the COVID-19 outbreak and long-range pollution on air quality in Bangkok Metropolitan, Thailand by using ground-based and satellite measurements such as MODIS and TROPOMI data. Moreover, the results project some possible future trends of air quality in Bangkok Metropolitan. The 24-hr average concentrations of PM2.5, O-3, NO2, CO and SO2 were compared between the periods of Normal, Lockdown and New Normal. PM2.5 concentrations increased by 20.56% during the Normal period and decreased by -15.79% and -23.34% during the Lockdown and New Normal periods, respectively, compared to the same periods in 2017-2019. There were also significant decreasing trends in O-3: -7.13% and 4.72%;and CO: -8.01% and 23.59% during the Lockdown and New Normal periods, respectively, while NO2 and SO2 concentrations showed increasing trends during the three periods. The MODIS and TROPOMI data analyses indicate the COVID-19 outbreak has had significant positive impact on surface pollution, but no impact on upper atmospheric pollution due to added pollution from long-range transport. The results also demonstrate that surface air pollution had a combination effect from biomass burning, traffic, industrial and household sources during the Lockdown period, except for SO2 concentrations, which were attributed to long-range transport pollution loading. In some cases, a negative impact of the COVID-19 lockdown on air pollution can be observed due to certain activities increasing within Bangkok Metropolitan. Additionally, the results also show that changing the lifestyle into a "new normal" for people in Bangkok after the Lockdown period has had a positive effect on air pollution.