The Chemical Composition Of Airborne PM₁₀ In Xiangtan City And Its Effects On Formation Of Acid Rain

In this work, samples of atmospheric particle matter (PM10) and precipitation in autumn and winterof Xiangtan city were collected. Atomic adsorption spectrophotometer (AAS) and ion chromatograph(IC) were used to analyze the chemical composition of heavy metals and negative ions of PM10andprecipitation samples, respectively. This paper aims to investigate the chemical composition ofatmosphere and how the chemical composition of atmosphere influences the formation of acid rain.Based on these analysis results, it is possible to make the following tentative conclusions:Air pollution was quite serious in Xiangtan city, and PM10mean concentration of atmosphere inwinter was significantly higher than that in autumn, which was299.629,209.072μg/m3, respectively. Inaddition, the PM10mean concentration of atmosphere may be correlated with the relative air humidityand temperature during sampling. Under certain condition, the PM10concentration had positivecorrelation with the humidity, and had negative correlation with the temperature.From the AAS analysis, the PM10pollution caused from the eight main kinds of heavy metals wasserious, and this pollution in winter was more serious than that in autumn. Among these heavy metals, theconcentration of Fe element was the highest, followed by Zn, Pb, Mn, Cr, Cu, Cd and Ni. Theconcentrations of Fe, Zn and Pb element in winter and autumn were6.69and6.712μg/m3,2.38and1.511μg/m3,0.227and0.441μg/m3, respectively. Water-soluble ion concentrations of PM10weredetected, and the concentration of four main kinds of ions was in this order: SO42-(high), NO3-, Cl-, andF-. This shows that the contamination sources of Xiangtan city are mainly from coal fly ash andautomotive emissions.Another result showed that the average pH of rain waters in winter and autumn was5.6and thefrequency of acid rains in winter and autumn was66.7%. The study also found the concentration of fourmain kinds of negative ions decreased at this sequence: SO42-, NO3-, Cl-and F-, of which SO42-accountedfor80%. This shows the main kind of acid rain of Xiangtan city is sulfuric acid rain, which is mainlycaused by some coal plants. Heavy metals in the precipitation of Fe, Pb, Cu, Mn content was relativelyhigh, other heavy metal element content was relatively low, even lower than the minimum detection limitinstrument.PM10and precipitation samples, the water-soluble anion SO42-and NO3-was one of the mainingredients, anion SO42-and NO3-both correlation was very good also, show that precipitation ofatmospheric PM10has obvious washed to remove effect, water-soluble ions in rain waters are mainlyfrom those dissolved particulate matters in atmosphere, among which it is the dissolved sulfates andnitrates, especially sulfates that lead to the formation of acid rains. among which the correlations withSO42-and NO3-was the biggest, showing0.812and0.671, Indicates that the acid rain in the study area isstrongly influenced by atmospheric PM10pollution degree.