Abstract
This study aimed to investigate aerosol chemical characteristics and to obtain the chemical profile of near-source biomass burning (BB) aerosols at a site (675 m a.s.l.) in Sonla, Northern Vietnam. Particulate matter (PM) with an aerodynamic diameter less than or equal to 2.5 μm (PM_(2.5)) was collected over a 24 h sampling period as part of the Seven South East Asian Studies (7-SEAS) campaign. The studies were conducted when BB was highly active - that is, in the spring of 2012 and 2013. The collected particles were analyzed for carbonaceous fractions and water-soluble components, in addition to the mass concentration. Data obtained were further analyzed to determine the stable species profile by classifying the 5-day air-mass backward trajectories. The average PM_(2.5) mass concentrations were 51 ± 19 μg m^(-3) and 57 ± 27 μg m^(-3) in 2012 and 2013, respectively. Carbonaceous contents dominated BB aerosol, with 59% ± 9% and 58% ± 9% in organic carbon (OC) and 9% ± 3% and 10% ± 3% in elemental carbon (EC) of PM_(2.5) in 2012 and 2013, respectively. Of the 8 carbonaceous fractions analyzed thermo-optically for PM_(2.5), OC3 (evolution temperature at 280°C-480°C) was most abundant in OC fractions, and EC1-OP (elemental carbon evolved at 580°C minus the pyrolized OC fractions) was predominant in EC fractions in most occasions. Among the measured water-soluble inorganic ions, NH_4^+ and SO_4^(2-) widely varied, indicating the influence of different trajectory origins. This finding was confirmed by trajectory classification of aerosol data. The trajectories were also distinguished with respect to char-EC to soot-EC ratio, and water-soluble OC. These characteristics were highest in the trajectory from the BB source area.
Highlights
This study aimed to investigate aerosol chemical characteristics and to obtain the chemical profile of near-source biomass burning (BB) aerosols at a site (675 m a.s.l.) in Sonla, Northern Vietnam
This study is aimed at finding signature profiles from the near-source BB aerosol, with reference to the composition of carbonaceous fractions and water-soluble inorganic ions (WSIs) in PM2.5 collected in Sonla, Northern Vietnam in 2012 and 2013
Other studies reporting on the influence of BB activity in Indochina Peninsula have shown that the PM2.5 mass concentrations of 24 ± 13 μg m–3 in Phimai, Thailand (Li et al, 2013), 30 ± 24 μg m–3 in southeastern Tibetan Plateau, China (Engling et al, 2011), and 17 ± 8 μg m–3 at Mt
Summary
Biomass burning (BB) has been established as a significant source of particulate matter (PM) and trace gases in the atmosphere (Andreae and Merlet, 2001; Koe et al, 2001; Streets et al, 2003; Crounse et al, 2009; Chuang et al, 2013a, b; Chuang et al, 2014). Major components of BBinfluenced PM2.5 (PM with an aerodynamic diameter less than or equal to 2.5 μm) include carbonaceous contents [both organic carbon (OC) and elemental carbon (EC)] (Cao et al, 2005; Lee et al, 2011; Chuang et al, 2013a, b; Mkoma et al, 2013; Chuang et al, 2014) These studies distinguished the emission sources by estimating the fractions of carbonaceous contents. OC2 is the most abundant carbon fraction in motor vehicle exhausts and coal combustion, as reported by Chow et al (2004) and Cao et al (2005), respectively. Chuang et al (2014) have recently differentiated the carbon fractions between the BB and non-biomass-burning (NBB) periods and reported that OC3 and EC1-OP are enriched in OC and EC for BB aerosol, whereas OC2 and EC2 occur more than other fractions in OC and EC for NBB aerosol
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