Investigation of biomass burning chemical components over Northern Southeast Asia during 7-SEAS/BASELInE 2014 campaign

This study investigates the chemical components of biomass burning (BB) aerosols obtained from Doi Ang Khang (DAK; near BB source) and Chiang Mai University (CMU; an urban location) over northern Southeast Asia in dry season (March to mid-April) 2014. PM_2.5 (particulate matter with an aerodynamic diameter less than or equal to 2.5 μm) samples were collected over a 24-h sampling period as a part of the Seven South East Asian Studies (7-SEAS)/BASELInE (BB Aerosols & Stratocumulus Environment: Lifecycles & Interactions Experiment) campaign. The collected aerosols were analyzed for mass concentrations of ions, metals and levoglucosan. The influence of air mass movements on aerosol species was also analyzed. The average PM_2.5 mass concentrations at DAK (80.8–83.3 μg m^–3) and CMU (90.7–93.1 μg m^–3) were not significantly different (p > 0.05) and well correlated (r = 0.8), and likely originated from similar source origins. The number of fire hotspots was particularly high during 20–21 March (greater than 200) and, consequently, peaks of PM_2.5 were recorded at both sites. The most abundant elements at both sampling sites were K (49–50% of total elements), Al (26–31%), Mg (16%) and Zn (4–7%), whereas SO₄^2–(30–38% of total ions), NO₃^–(13–20%), Na⁺ (16–20%) and NH₄⁺ (14–15%) were the most abundant ions. Concentrations of levoglucosan and K⁺ (BB tracers) were well correlated (r = 0.5 for CMU and 0.7 for DAK) confirming that the PM_2.5 detected in these areas were mainly influenced by BB activity. Principal component analysis (PCA) revealed that BB, road traffic, agricultural activity and soil re-suspension were plausible sources of PM_2.5 over the study locations. Apart from local sources, the influence of long-range transport was also investigated by way of three-day backward trajectory analysis.