Abstract
ABSTRACT Northern Thailand has long been severely affected by haze from biomass burning containing fine and ultrafine aerosols in the dry period. The carbonaceous PM0.1 comprising elemental carbon (EC) and organic carbon (OC) collected during the haze and non-haze periods in Chiang Mai, Thailand was investigated. The PM0.1 levels during the haze periods were about 3 times higher than the non-haze periods, a significant increase. PM0.1 concentration was strongly correlated with atmospheric relative humidity and the number of forest fire hotspots. Carbonaceous aerosol characteristics in PM0.1 were analyzed with the thermal/optical transmittance (TOT) method following the IMPROVE protocol. The concentrations of OC and EC, distribution of OC and EC and OC/EC ratios in PM0.1 were evaluated. Average OC and EC mass concentrations in PM0.1 were 6.8 ± 2.7 and 1.4 ± 0.5 µg m–3 during the haze periods, significantly higher than those during the non-haze periods; 1.9 ± 0.9 and 0.5 ± 0.2 µg m–3. The OC/EC ratio increased linearly with the number of hotspots. This indicated significant contribution from biomass burning to the PM0.1. This was strongly supported by the 48-hr backward trajectory simulation, that indicated both domestic and transboundary aerosol transports. Because both organic and elemental carbon are the light-absorbing carbonaceous aerosols, the increase during the haze periods contributed to regional air quality and climate. This study enhances the understanding of PM0.1 behavior in Chiang Mai, Thailand, during the haze periods in upper southeast Asia.
Highlights
The current ambient air quality standard of particulate matters focuses on PM2.5 mass concentrations
In the upper Southeast Asia (SEA), the haze is observed during the first quarter of every year and studied, mostly in Thailand (Wiriya et al, 2013, 2016; Thepnuan et al, 2019; Pani et al, 2019), but recently, air quality affected by PM10 and PM2.5 was studied in Laos (Nguyen et al, 2019), Myanmar (Sricharoenvech et al, 2020) and Vietnam (Le, 2020)
Ambient PM2.5 concentrations were compared to those monitored by the Thailand Pollution Control Department (PCD), located in Mueang District, Chiang Mai Province (18.79°N, 98.98°E), 3.6 km SE of the sampling site
Summary
The current ambient air quality standard of particulate matters focuses on PM2.5 mass concentrations. A recent study in Thailand showed that PM0.1 represented more than 5.7–14.8% of total suspended particulates (TSP) in atmospheric air (Chomanee et al, 2020). In the upper SEA, the haze is observed during the first quarter of every year and studied, mostly in Thailand (Wiriya et al, 2013, 2016; Thepnuan et al, 2019; Pani et al, 2019), but recently, air quality affected by PM10 and PM2.5 was studied in Laos (Nguyen et al, 2019), Myanmar (Sricharoenvech et al, 2020) and Vietnam (Le, 2020). Domestic sources of haze phenomena in northern Thailand were predominantly from forest fires, which occurred mostly in deciduous dipterocarp forest national parks, whereas the agricultural waste burning was minor. Forest fires in northern Thailand adversely affected the livelihood of people, leading to significant poverty
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