Particle-bound organic and elemental carbons for source identification of PM < 0.1 µm from biomass combustion.

Atmospheric nanoparticles (PM < 0.1 µm) are a major cause of environmental problems and also affect health risk. To control and reduce these problems, sources identification of atmospheric particulates is necessary. Combustion of bituminous coal and biomass including rubber wood, palm kernel, palm fiber, rice stubble, rice straw, maize residue, sugarcane leaves and sugarcane bagasse, which are considered as sources of air quality problems in many countries, was performed. Emissions of particle-bound chemical components including organic carbon (OC), elemental carbon (EC), water-soluble ions (NH4+, Cl-, NO3-, SO42-), elements (Ca, K, Mg, Na) and heavy metals (Cd, Cr, Ni, Pb) were investigated. The results revealed that PM < 0.1 µm from all samples was dominated by the OC component (>50%) with minor contribution from EC (3%-12%). The higher fraction of carbonaceous components was found in the particulates with smaller sizes, and lignin content may relate to concentration of pyrolyzed organic carbon (PyOC) resulting in the differences of OC/EC values. PM emitted from burning palm fiber and rice stubble showed high values of OC/EC and also high PyOC. Non-carbonaceous components such as Cl-, Cr, Ca, Cd, Ni, Na and Mg may be useful as source indicators, but they did not show any correlation with the size of PM.

The influence of the open burning of agricultural biomass and forest fires in Thailand on the carbonaceous components in size-fractionated particles.

Size-segregated ambient particles down to particles smaller than 0.1 µm (PM0.1) were collected during the year 2014-2015 using cascade air samplers with a PM0.1 stage, at two cities in Thailand, Bangkok and Chiang Mai. Their characteristics and seasonal behavior were evaluated based on the thermal/optical reflectance (IMPROVE_TOR) method. Diagnostic indices for their emission sources and the black carbon (BC) concentration were assessed using an aethalometer and related to the monthly emission inventory (EI) of particle-bound BC and organic carbon (OC) in order to investigate the contribution of agricultural activities and forest fires as well as agro-industries in Thailand. Monthly provincial EIs were evaluated based on the number of agricultural crops produced corresponding to field residue burning and the use of residues as fuel in agro-industries, and also on the number of hot spots from satellite images corresponding to the areas burned by forest fires. The ratio of char-EC/soot-EC describing the relative influence of biomass combustion to diesel emission was found to be in agreement with the EI of BC from biomass burning in the size range <1 µm. This was especially true for PM0.1, which usually tends to be indicative of diesel exhaust particles, and was shown to be very sensitive to the EI of biomass burning. In Chiang Mai, the northern part of Thailand, the forest fires located upwind of the monitoring site were found to be the largest contributor while the carbon behavior at the site in Bangkok was better accounted for by the EI of provinces in central Thailand including Bangkok and its surrounding provinces, where the burning of crop residues and the cultivation of sugarcane for sugar production are significant factors. This suggests that the influence of transportation of polluted air masses is important on a multi-provincial scale (100-200 km) in Thailand.