Physical and chemical characteristics of particulate matter at various sizes in Chiang Mai ambient air

Abstract

Particulate matter samples of Chiang Mai ambient air were collected from three sampling sites (site 1: Yuparaj School, site 2: municipality hospital and site 3: the district office of Sarapee), and fractionated into five size fractions (PM>10, PM[subscript 2.5-10, PM[subscript 1.0-2.5], PM[subscript 0.5-1.0], and PM[subscript 0.1-0.5 micrometre) with a high volume cascade impactor during mid-June 2005 to January 2006. The quantity and size distribution of the samples were investigated by gravimetric method using analytical balance. Ions (Na[superscript +], NH[subscript 4][superscript +], K[superscript +], Mg[superscript 2+], Ca[superscript 2+], CI[superscript -], NO[subscript 3][superscript -], SO[subscript 4][superscript 2-]) and PO[subscript 4][superscript 3-]) and metals (Al, B, Ba, Ca, Fe, K, Li, Mg, Mn, Na, Pb, Sr, Ti and Zn) were chemical compositions of the samples which have been analyzed. The techniques used for ions analyzing (anions and cations) and metals analyzing was ion chromatography and inductively coupled plasma-optical emission spectroscopy, respectively. Finally, the relationship between each size fractions of PM and the sampling sites were investigated as well as the temporal variations by a statistical program. The average 24-hr PM[subscript 10] concentrations during the sampling period at the sampling site 1, 2 and 3 were 29.74-79.38 (48.68), 30.87-109.81 (58.88) and 30.71-92.94 (60.99) microgram/m[superscript 3], respectively. In addition, the average 24-hr PM[subscript 2.5] concentrations were 14.14-44.05 (25.62), 13.87-63.55 (31.40) and 18.11-68.26 (37.15) microgram/m[superscript 3], respectively. It was noted that PM[subscript 2.5] concentrations at sampling site 3 exceeded the standard daily average PM[subscript 2.5] of US.EPA. Metal components were highly found in coarse particle (PM[subscript 2.5-10]) that in fine particle (PM[subscript 0.1-2.5]). The portion of PM>10:PM[subscript 2.5-10]:PM[subscript 0.1-2.5] was 36:44:20. Conversely, ions were found in fine particle more than in coarse particle. The portion of PM>10:PM[subscript 2.5-10]:PM[subscript 0.1-2.5] was 18:28:54 and 26:15:59 for anions and cations, respectively. The dominant compositions in PM observed in this study were Ca, Al, Fe, Cl[superscript -], NO[subscript 3][superscript -], SO[subscript 4][superscript 2-], NH[subscript 4][superscript +] and K[superscript +]. Moreover, the study of relationship between the level of PM concentrations, the sampling sites and temporal variations found that each size fractions of PM had high correlation to other fractions (r = 0.353-0.840, p<0.05). It was found that concentrations of fine particle collected from site 1 were significantly different from the concentrations at site 3 (F = 3.569, p<0.05). The concentrations of PM during dry season were higher than the concentrations collected in wet season for all size fractions and were significantly different (F = 5.124-30.159, p<0.05). The study of relationship between the concentrations of PM's compositions, the sampling sites and temporal variations found that site 1 and site 3 had different quantity of some compositions at the significance level of 0.05 (F = 5.875-6.059, p<0.05). Seasonal variations also caused significantly different in concentrations of some PM's compositions (F = 4.121-23.286, p<0.05). The study of size distribution of particulate matter in Chiang Mai indicated that the type of distribution was bi-modal and there were 2 groups of distribution patterns. Sampling site 1 and 2 (city areas) had the same pattern of distribution but it was different at sampling site 3 (rural areas). Since there was highly in proportion of fine particle at sampling site 3, then the size distribution of PM in this area had a higher peak of the bi-modal distribution at around 0.5-1.0 micrometre while the others had a higher peak at around 2.5-10 micrometre.