Ambient PM2.5, Polycyclic Aromatic Hydrocarbons and Biomass Burning Tracer in Mae Sot District, Western Thailand
Levoglucosan, as a biomass tracer, and sixteen polycyclic aromatic hydrocarbons (PAHs) in PM2.5 ambient air samples collected from Tak Province during smoke and non-smoke episodes were analyzed. The average PM2.5, levoglucosan and total PAHs concentrations in the smoke episode were 61.64 ± 22.85, 1.00 ± 0.41 μg/m3 and 6.32 ± 2.26 ng/m3, respectively. This figures were significantly higher than those recorded during the non-episode (13.76 ± 5.58, 0.12 ± 0.03 μg/m3 and 2.59 ± 0.15 ng/m3, respectively).
The predominant PAHs proportions were comprised of Phenanthrene and Benzo[ghi]perylene and levoglucosan concentrations revealed a strong correlation with PM2.5 concentrations, which indicated the source of PM2.5 from biomass burning. Toxicity equivalent (TEQBaP) and the mutagenic equivalent (MEQBaP) levels during the smoke episode were significantly higher than those in the non-smoke episode. Furthermore, lifetime lung cancer risk recorded during smoke episode exceeded the acceptable cancer risk that has been recommended by US-EPA. These results suggest that this area was not only exposed to PAHs that originated from traffic combustion, but was also exposed from biomass burning emissions, particularly during biomass burning season when there is an increased risks of cancer and mutation. Although the exposure time in this area is relatively short, the high dose period of exposure occurs repetitively every year. In addition, backward trajectories showed that most of the air mass was generated from western region of Thailand and they were throughout the burning region not only emitted from local areas, but also from outside the country during the smoke episode.