Chemical characteristics of water-soluble components in TSP over Guiyang, SW China, 2003

Total suspended particles (TSP) were collected in 2003 to study chemical characteristics of water-soluble inorganic ions (Cl−, NO3−, SO42−, NH4+, Ca2+, Mg2+) and water-soluble organic carbon (WSOC) in a karst city Guiyang, which suffers from serious acid rain problems. Concentrations of the TSP matter were 44.40–385.09 μg m−3, closely associated with relative humidity (RH). Water-soluble matters of TSP are acidic in nature in most days of 2003 except for those in summer, in which season high pH values were observed sometimes. SO42−, Ca2+ and NH4+ were the dominant ionic species, which accounted for 15.2%, 3.4% and 2.8% of TSP, respectively. SO42− is the most abundant chemical component (22.34±10.10 μg m−3) and accounts for about 53.6% of the total mass of ions. High SO42− levels and lower mass ratios of [NO3−]/[SO42−] in TSP (0.13±0.06) were found because of the wide use of sulfur-containing coal. The WSOC mass concentrations varied from 1.83 to 22.44 μg m−3, with an annual average of 5.72±3.69 μg m−3. WSOC mass concentrations are inversely correlated with air temperature (y=-0.14x+5.88,R=0.72). A good linear correlation between WSOC/TSP and pH of TSP (y=-1.79x+14.74,R=0.70) were also found in Guiyang when pH are lower than 8. WSOC/TSP of basic TSP (pH>8) are within the range of 1.5–3.5%. Lower mass concentrations of all water-soluble inorganic ions and WSOC were observed in rainy days relative to those in not rainy days, while their mass percentages in TSP are higher in rainy days for SO42−, NH4+, Ca2+ and Mg2+. It indicates that suspended matters with lower concentrations of these ions are preferentially scavenged into rainfalls.