Chemical characterization and source apportionment of PM\(_{2.5}\) bound with primary and secondary organic compounds during haze and post-haze over the nothern Thailand

Saksakulkrai, Supattarachai ORCID: 0000-0002-3422-9896 (2024). Chemical characterization and source apportionment of PM\(_{2.5}\) bound with primary and secondary organic compounds during haze and post-haze over the nothern Thailand. University of Birmingham. Ph.D.

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Abstract

Northern Thailand has been facing recurrent haze events every year during the local summer season over the past few decades. Biomass burning, a well-known major source of this problem resulting from unsuitable agricultural practices, has caused several adverse impacts on human health, the environment, and socioeconomic aspects. Despite efforts, zero burning policy over northern Thailand has not been successfully implemented, as the haze persists for extended periods. In this research, daily PM\(_{2.5}\) was collected at a rural site in Chiang Mai, northern Thailand during haze and post-haze periods in 2019. Bulk chemical components and organic tracers were measured, including organic carbon (OC), elemental carbon (EC), water soluble inorganic ions (WSIIs), crustal and trace elements, nonpolar and polar organic compounds. Average mass of PM\(_{2.5}\) were 87 ± 36 and 21 ± 11 μg m-3 during haze and post-haze, respectively. Mass closure shows that during haze and post-haze, organic matter, water-soluble inorganic ions, and mineral dust were the top three contributors in PM\(_{2.5}\) mass. Source apportionment by positive matrix factorization (PMF) with organic tracers identified three different biomass burning sources including general biomass burning, nearby biomass burning (fresh aerosol), and softwood burning (aged aerosol) and three other sources including secondary sulfate, mixed dusts and traffic related emissions, and secondary nitrate, with contributions of 31%, 19%, 13%, 17%, 15%, and 5% during haze and 5%, 32%, 1%, 34%, 26%, and 2% during post-haze, respectively. Estimated lifetime cancer risk from exposure to PM\(_{2.5}\) bound PAHs ranged in moderate risk for the whole period. Biomass burning, softwood burning, and diesel combustion were the most contributor to lifetime cancer risk during haze, while diesel and gasoline combustions were the most contributors during post-haze. Several polar organic compounds display secondary organic aerosols characteristic especially dicarboxylic acids and nitrated aromatic phenols. The ratio of malic acid to succinic acid indicates stronger photooxidation during post-haze than haze period. Future study requires a longer sampling period in non-haze and different site environments for comparison and should be applied with remote sensing information. PMF model is recommended for source apportionment with comprehensive chemical species and organic tracers. Both gas and particulate phases Polycyclic Aromatic Hydrocarbons (PAHs) are recommended for lifetime cancer risk assessment.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):