Strontium isotope and major ion chemistry of the rainwaters from Guiyang, Guizhou Province, China

Twenty-two rainwater samples from Guiyang city, southwestern China, have been analyzed for their chemical compositions and 87Sr / 86Sr ratios, with a main purpose to get a better understanding of the general features of rainwater in Guiyang city and their correspondences to human activities. The rainwaters studied are almost acidic (pH = 4.53) and show big changes in major ion composition. Ca2+ and Mg2+ are the principal cations in the rainwaters and their mean values are 56.6 μmol/L (12.5–163.8 μmol/L) and 12.8 μmol/L (4.5–47.3 μmol/L ), respectively. The sum of Ca2+ and Mg2+ accounts for 78%–96% of the total cations in the studied rainwaters. Na+ was the least abundant of the major cations with a mean content of 4 μmol/L (0.9–7.8 μmol/L). SO42− is the predominant anion, with a mean content of 94 μmol/L (33.5–279.4 μmol/L), coming next is NO3− with a mean content of 48 μmol/L (2.1–251.8 μmol/L). SO42− and NO3− together account for 77%–99% of the total anions.Ca2+ and Mg2+ in the rainwater are most likely from dissolution of carbonate minerals in dust or aerosol, unlike K+ that shows more contribution of anthropogenic sources to the rainwater. Na+ does not vary in concentration with Cl−. Significant enrichment of Cl− relative to Na+ as compared with sea water indicates negligible contribution of marine source, which is supported by the evidence that the total rainwater samples show lower 87Sr / 86Sr ratios (ranging from 0.707934 to 0.709080) than sea water. The rainwater samples are characterized by high contents of NO3−, SO42−, and Cl− relative to Na+, as compared to the rainwater from other areas in the world, suggesting that the anions (NO3−, SO42−, and Cl−) have mainly of anthropogenic sources. Sr isotope shows potential to trace sources of contaminants when combined with other chemical factors: covariation of 87Sr / 86Sr ratio with Cl− / Na+ in the rainwater suggest presence of at least two anthropogenic sources for the rainwater samples studied. The coal-combustion industries are probably the major atmospheric contaminant sources in Guiyang city.