| dc.description.abstract | Every spring, biomass burning (BB) is very active in the northern Indochina peninsula. Atmospheric aerosol was collected at Sonla, northern Vietnam (675 m a.s.l.) during 7-SEAS (Seven SouthEast Asian Studies) campaign in 2013. The objective of this study was to investigate comprehensively the chemical characteristics of near-source BB aerosol in the northern Vietnam where related data were scarce.
During the BB period, the results revealed that PM2.5 (particulate matter with an aerodynamic diameter less than or equal to 2.5 μm) dominated PM10 at Sonla in 2013 (mean: 57 ± 27 μg m-3, range: 13—134 μg m-3) with a PM2.5 to PM10 ratio of 0.75 ± 0.09. With regard to bulk water-soluble inorganic component, SO42- is the dominated specie, the average concentration was 5.51 ± 2.43 μg m-3, accounting for 11.04 ± 5.62 % in PM2.5 mass, followed by NH4+ (1.94 ± 0.94 μg m-3, 4.09 ± 2.52 %), NO3- (1.18 ± 0.57 μg m-3, 2.13 ± 0.80 %), and K+ (1.18 ± 0.57 μg m-3, 1.87 ± 0.53 %). As for the bulk carbonaceous content, organic carbon (OC) and elemental carbon(EC) were averaged at 20.16 ± 9.57 μg m-3 (35.62 ± 6.64 %) and 3.45 ± 1.77 μg m-3 (6.22 ± 2.03 %), respectively; OC3 was the most significant fraction in OC and EC1-OP was dominated in elemental carbon (EC) fractions. Furthermore, the high water-soluble OC (WSOC) fraction in OC (56 ± 12%) implies that carbonaceous aerosol from BB plume would be potentially hygroscopic. Humic-like-substances (HULIS), known as light-absorbing-organic component, was found at 7.40 ± 4.54 μg m-3, constituting 35 ± 9% in OC. Meanwhile, levoglucosan, as a biomass burning marker, is noted as the predominant species in aerosol anhydrosugars, averaged at 1.80 ± 0.96 μg m-3 (3.09 ± 0.72%). The linear correlation matrix of the near-source BB tracers such as K+, OC3, EC1-OP, HULIS and levoglucosan were correlated well with each other (R2≧0.62, N=44), indicating that aerosols were influenced intensively by BB in the area.
By employing the ratio of PM2.5 levoglucosan to mannosan, averaged at 15.6 ± 1.4 during the study period at the Sonla site, as well as 14 selected samples for the analysis of BB markers by gas chromatography–mass spectrometry, the major burnt materials was inferred to be from hardwood and grass/non-woody vegetation.
The temporal variations of both primary and secondary aerosol tracers from the 14 selected samples were also identified. More than 50 organic compounds including saccharide compounds, lignin and resin products, fatty acids, aromatic acids, poly-acids, and biogenic oxidation products (e.g., 2-methyltetrols, alkene triols, 3-hydroxyglutaric acid) were resolved in the aerosol particles. By comparing the tracers of aerosol samples classified with backward airflow trajectories from different source regions, one can better understand the influence of BB on the organic molecular composition of the transported aerosols and provide additional important information on aerosol sources and oxidation processes.
Finally, stable carbon δ13C isotopic data ranged from −26.6 to −25.4‰ in PM2.5 were revealed for the first time in the northern Vietnam, which indicated a contribution from burning of C3 plants and fossil fuel combustion
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