Characterization of Particulate Matter Measured at Remote Forest Site in Relation to Local and Distant Contributing Sources

ABSTRACT

This study characterized the particulate matter (PM) pollution at a forest site in the Khao Yai (KY) National Park of Thailand, 700 m above sea level and 120 km upwind to Bangkok during the dry season. Two dichotomous samplers simultaneously operated on each monitoring day to collect 2 samples (on 2 filter types: quartz and mix cellulose) of 24 h PM_2.5 and 2 samples of 24 h PM_10–2.5. More focus was on the dry and more polluted season with a longer sampling period (43 days: Jan–Feb 2005) and less on wet season (10 days, Jun 2005). Samples were analyzed for mass, water soluble ions, elements, EC and OC (Sunset analyzer). PM_2.5 levels obtained at KY in the dry period (47 µg m^–3) were comparable to those in several urban areas in Southeast Asia, but the wet season levels (7 µg m^–3) were significantly lower. In the dry season, levels of EC associated with PM_2.5 at KY were remarkably lower than but OC were comparable to those found in urban areas which resulted in considerably low EC/TC ratios (0.08). The major mass groups of PM_2.5 in the dry season were organic matter of biomass smoke origin (OM-smoke), secondary inorganic aerosol, organic matter of other origins than smoke (OM-others) and crustal. Similar contributors to PM_2.5 were also found in the wet season but with only a small contribution from biomass burning smoke. Significant contributions from distant sources to PM_2.5 levels measured at KY were also confirmed by the HYSPLIT backward trajectory analysis. The coarse fraction (PM_10–2.5) had major mass groups of OM-others, inorganic particles and crustal that were most likely related to local sources, and some amount of aged sea salt indicating a distant source origin.