Seasonal analysis of indoor and outdoor ratios of PM<inf>2.5</inf> and PM<inf>10</inf> in Bangkok and Chiang Mai: A comparative study of haze and non-haze episodes

Abstract

Particulate matter (PM) air pollution has been identified as one cause of human health impact with the estimated global 8.8 million attributable deaths. Thailand experiences haze episode every year, which can lead to high ambient concentrations of particulate matter in ambient air. This study aims to investigate the relationship of indoor and outdoor air quality in both haze and non-haze period in two cities in Thailand: namely Bangkok and Chiang Mai. We conducted the air quality sampling in various styles of house, with 17 houses in both urban and rural areas, between April to October 2019. The results indicated that the concentration of PM2.5 in indoor air in Bangkok were 19.85 and 11.40 μg/m3 for haze and non-haze period, respectively, whereas the PM10 concentrations were 32.124 and 17.49 μg/m3 for haze and non-haze period, respectively. The corresponding average of outdoor air concentrations were 26.26 and 16.68 μg/m3 for haze and non-haze, respectively. While the PM10 concentrations were 46.36 and 23.86 μg/m3 for haze and non-haze period, respectively. In Chiang Mai, it was observed that the mean concentration of PM2.5 in indoor was 106.80 μg/m3 and 5.52 μg/m3 for haze and non-haze periods, respectively. Regarding PM10, it was observed that the mean concentration in indoor was 118.54 μg/m3 and 9.74 μg/m3 for haze and non-haze periods, respectively. Indoor/Outdoor (I/O) ratios of PM2.5 varied in Bangkok average was 0.76 for haze and 0.68 for non-haze period. The I/O ratio in Chiang Mai was 0.91 and 1.16 for haze and non-haze episode, respectively. Indoor/Outdoor (I/O) ratios of PM10 varied in Bangkok average was 0.70 for haze and 0.73 for non-haze period. The I/O ratio in Chiang Mai was 0.92 and 0.96 for haze and non-haze episode, respectively Our findings indicated the influences of outdoor air quality on indoor air quality during both haze and non-haze episode. The intrusion of outdoor air in Chiang Mai to the houses caused a higher I/O ratio than Bangkok due to the characteristics of house and culture. The indoor air quality in terms of particulate matter were dominated by outdoor air quality. Thus, people should close doors/windows during the haze as well as non-haze episode to avoiding the pollutant accumulation.