Hardwood Burning as a Dominant Source of Fine Particulate Matter from Biomass Burning in Ho Chi Minh City, Vietnam

While biomass burning (BB) significantly affects air quality in Southeast Asia, its contribution to PM2.5 in Ho Chi Minh City (HCMC), Vietnam’s most populous city, remains poorly understood. This study aimed to identify the major BB sources contributing to PM2.5 in urban HCMC, with particular attention to the potential underestimation caused by chemical degradation of levoglucosan (Lev), a widely used BB tracer. PM2.5 samples were collected from October to December 2021 and analyzed for their chemical composition, including Lev, mannosan (Man), and potassium from BB (KBB+). The average PM2.5 mass concentration was 26.6 ± 8.8 μg m–3 and was higher during the dry season than the rainy season due to reduced wet deposition. Notably, evaluation of BB tracers indicated substantial chemical degradation of Lev, with an estimated loss of approximately 88%. After correcting for this degradation, the reconstructed Lev concentration without chemical loss (Levno-chem) reached 1766 ± 637 ng m–3. Diagnostic ratios of Lev/Man, Levno-chem/KBB+, and OC/Levno-chem were 16.7 ± 2.6, 1.76 ± 0.39, and 4.54 ± 0.74, respectively. Importantly, source identification based on the uncorrected Lev would have suggested crop residue and grass burning as the dominant BB sources. In contrast, the degradation-corrected ratios consistently indicate that hardwood and hardwood charcoal combustion from cooking are the predominant BB sources in HCMC. Weighted concentration weighted trajectory analysis further revealed that these emissions are primarily associated with local urban activities rather than long-range transport. These findings demonstrate that accounting for Lev degradation is essential for accurate BB source identification in Southeast Asia.