Analysis on representative chemical compositions of urban acid precipitation

A 5-year weekly data set on the ionic composition of rainwater from 3 sampling sites (Hunan University station, municipal environment monitoring station and Ma Po-ling station) in Changsha representing the 1998-2002 period was resolved by employing factor analysis, meanwhile the screened data were obtained on the basis of a cutoff ion balance of ±20%. Three-to-four factors explaining the cumulative variances of 79%-81% of the total in the 10 ionic parameters are utilized in the interpretation. The results indicate that the obtained factors from the screened data reflect the local environment more effectively; the Hunan University site has four factors a partially neutralized acid (PNA) component, a sea salt-base (SS) component, a vegetation/waste (V/W) incineration factor and an earth (Earth) one. The free acidity of rainwater of municipal environment monitoring station site is contributed by other than H2SO4 and HNO2, possibly by HF and HCl acids among some others; Ma Po-ling site's results show that the major acid precursor substance is NOx, however, SO4^2- appears in the form of Na2SO4 and (NH4)2SO4. The sites of Hunan University and Ma Po-ling have the same Ca²⁺ sources, i.e. the construction and building industry.