Abstract
Samples of 24 h PM_(10) and PM_(2.5) were collected at a mountainous rural site of Tamdao, Vietnam, using collocated dichotomous and MiniVol samplers. The sampling was done in wet season (20 September-8 October 2005), dry season (17 December 2005-18 January 2006) and transitional season (5 April-26 April 2010). A pair of PM_(2.5) and PM_(10-2.5) or PM_(10) samples was collected on a sampling day using quartz and mixed cellulose filters for each size fraction. The samples were analyzed for mass, BC, water soluble inorganic ions and elemental compositions. Higher PM_(2.5) levels were obtained during dry season, at an average of 51 μg/m^3 , followed by the transitional season, 33 μg/m^3, and the lowest in wet season, 25 μg/m^3. The ratios between anions and cations, both in equivalence, were all below 1.0, but was higher for PM_(2.5) than for PM_(10-2.5). The ammonium balance showed a good agreement between measured and estimated levels for PM_(2.5), suggesting that most of sulfate and nitrate were in their ammonium salts. The reconstructed mass showed high contributions from secondary inorganic particles , OM-biomass (estimated based on K^+), crustal and soot groups, which accordingly helped to reveal major contributing sources. Specifically, the high K-biomass and OM-biomass mass group in the dry season indicated the important contribution from biomass burning. The regional transport from surrounding territories to the site was investigated using 5-day HYSPLIT backward trajectories. The differences in PM mass and compositional species that were statistically significant between the seasons for similar trajectory patterns, or between patterns within a season, suggested the effects of seasons and/or air mass trajectory pathways on PM pollution. The northeast continental type of air masses observed in the dry season, with the longest continental pathway and continental origin, was associated with the highest levels of PM mass and compositional species.
Highlights
0.14 c) Between the SEM1-w and SEM2-w observed in wet season
0.11 -0.45 0.18 e) Between SEM1-w and NEC-w observed in the wet season
0.89 0.37 t -2.17 df 10.00 t-test for Equality of Means
Summary
ΜEq/m3 c) Ion balance for PM2.5, wet season E) Ion balance, PM2.5 transitional season 0.2 y = 0.6126x b) Ion balance, PM10-2.5, dry season 0.4 y = 0.3931x + 0.0556 D) Ion balance, PM10-2.5, wet season 0.15 y = 0.4353x f) Ion balance, PM10, transitional season 0.25
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