Observational Research Of Acetate And Formate In Precipitation

Acid rain has been being one of the hot issues in atmospheric environment researches. This work is part of the National Basic Research Program of China: Characteristics and Evolution of Chemical Components in Precipitation in Typical Climatic and Ecological Regions. Fourteen typical stations were selected for the observation of acid rain. Organic (formic and acetic) acids as well as major inorganic anions in precipitation were analyzed and the characteristics of chemical components in wet deposition in these regions were obtained.An analysis method based on the gradient elution ion chromatography was established by experiments. The method can relatively fast and effectively separate and detect formate, acetate, and major inorganic anions in precipitation samples. The performance of the method was evaluated by experiments and found good. The effectiveness of CHCl3 and Thymol in preserving organic acids in rainwater and the stability of stock solutions of formate and acetate were tested. QA&QC methods were strictly implemented to ensure the data quality. Based on the measurements from 2007, the mean concentrations of formate at 14 stations were in the range of 0.962-3.43μmol·L-1, and those of acetate were in the range of 0.00-5.13μmol·L-1. The mean concentrations of formate and acetate were not differed significantly from region to region. Seasonal variations of formate and acetate at different stations were not always consistent with each other. The annual wet depositions of formate and acetate were estimated to be in the ranges of 0.382-4.18mmol·m-2 y-1 and 0.058-5.87 mmol·m-2 y-1, respectively, with larger depositions in southern China and smaller depositions in northern China. The relative contributions of the two organic acids to the total acidity of precipitation were estimated to be in the range of 0.02%-99.1%, with an average of 17.2%, suggesting that organic acids should not be neglected in terms of acidification of rainwater. Including data of formate, acetate, and HCO3- significantly improved the ion balance between the sum of anions and that of cations. For some stations, however, ion imbalance still exists to a certain degree, with the sum of cations larger than that of anions.Correlation analysis and factor analysis were applied to ion components data from different stations. The results were used to identify the likely sources of those components in rainwater. The calculated ratios formate/acetate and their seasonal variations imply that the organic acids in precipitation in most Chinese regions were dominantly emitted by anthropogenic sources and that biogenic sources are dominant only in growing season in the remote and well vegetated region.