Impact of transport of fine and ultrafine particles from open biomass burning on air quality during 2019 Bangkok haze episode

Transboundary and domestic aerosol transport during 2018–2019 affecting Bangkok air quality has been investigated. Physicochemical characteristics of size-segregated ambient particles down to nano-particles collected during 2017 non-haze and 2018–2019 haze periods were analyzed. The average PM_2.5 concentrations at KU and KMUTNB sites in Bangkok, Thailand during the haze periods were about 4 times higher than in non-haze periods. The highest average organic carbon and elemental carbon concentrations were 4.6 ± 2.1 µg/m³ and 1.0 ± 0.4 µg/m³, respectively, in PM_0.5–1.0 range at KU site. The values of OC/EC and char-EC/soot-EC ratios in accumulation mode particles suggested the significant influence of biomass burning, while the nuclei and coarse mode particles were from mixed sources. PAH concentrations during 2018–2019 haze period at KU and KMUTNB were 3.4 ± 0.9 ng/m³ and 1.8 ± 0.2 ng/m³, respectively. The PAH diagnostic ratio of PM_2.5 also suggested the main contributions were from biomass combustion. This is supported by the 48-hrs backward trajectory simulation. The higher PM_2.5 concentrations during 2018–2019 haze period are also associated with the meteorological conditions that induce thermal inversions and weak winds in the morning and evening. Average values of benzo(a)pyrene toxic equivalency quotient during haze period were about 3–6 times higher than during non-haze period. This should raise a concern of potential human health risk in Bangkok and vicinity exposing to fine and ultrafine particulate matters in addition to regular exposure to traffic emission.     

Characteristics of nanoparticles emitted from burning of biomass fuels

The characteristics of the particles of the smoke that is emitted from the burning ofbiomass fuels were experimentally investigated using a laboratory-scale tube furnace and different types of biomass fuels： rubber wood, whole wood pellets and rice husks. Emitted amounts of particles, particle-bound polycyclic aromatic hydrocarbons （PAHs） and water-soluble organic carbon （WSOC） are discussed relative to the size of the emitted particles, ranging to as small as nano-size （〈70 nm）, and to the rate of heating rate during combustion, differential thermal analysis （DTA） and thermogravimetric analysis （TG） techniques were used to examine the effect of heating rate and biomass type on combustion behaviors relative to the characteristics of particle emissions. In the present study, more than 30% of the smoke particles from the burning ofbiomass fuel had a mass that fell within a range of 〈 100 nm. Particles smaller than 0.43 μm contributed greatly to the total levels of toxic PAHs and WSOC. The properties of these particles were influenced by the fuel component, the combustion conditions, and the particle size. Although TC--DTA results indicated that the heating rate in a range of 10-20℃did not show a significant effect on the combustion properties, there was a slight increase in the decomposition temperature as heating rate was increased. The nano-size particles had the smallest fraction of particle mass and particle-bound PAHs, but nonetheless these particles registered the largest fraction of particle-bound WSOC.