摘要
根据平衡热力学理论,考虑温度(T)、压强(P)和离子强度(I)等因素的影响,提出了一种新的有机酸对降水自由酸度贡献的计算方法(热力学平衡计算法),评价了上述三个因素的变化对有机酸酸度贡献量的影响.研究表明:(1)只有当降水pH≤5时,才能有效计算有机酸对降水自由酸度的贡献,这是有机酸对酸度产生贡献的前提;(2)pH值对有机酸酸度贡献有着直接而主要的影响;其次是T,它对甲酸和乙酸酸度贡献的相对偏差可分别高达9.4%和32.0%;(3)当P变化不大(0.870×105—1.013×105Pa)时,其对有机酸酸度贡献的影响可以忽略,而I对有机酸酸度贡献几乎无影响,即忽略降水中离子之间的相互作用;(4)对比显示,已有方法计算所得的有机酸酸度贡献结果仅仅是本方法在298.15K和1.013×105Pa且忽略碱性离子中和情况(X%=0)的条件下所计算出结果的一种特例.
Guiyang, 550002, China; Organic acids, in particular, formic and acetic acids, are ubiquitous constituents in precipitation. They make important contributions to free acidity （FA） of precipitation. Various methods such as indirect method, concentration-ratio method, maximum contribution method and direct contribution method have been reported to estimate the contribution of organic acids to FA. Though those methods are extensive, they ignored factors such as temperature （T）, pressure （P）, and ion strength （I） in precipitation. To overcome these problems, we propose thermodynamics equilibrium calculation method （TECM） to calculate organic contribution to FA and evaluate the effect of T, P and I. Results showed as follows： （1） only precipitation samples with pH ≤5 would be considered to calculate organic contribution. Because when pH ≤5, organic acids would dissociate liberated H^ ＋. （2） The pH value was the most direct and important impact factor for the contribution, followed by T. Different T could lead to different contributions of formic and acetic acids to FA with relative standard deviation of 9. 4 % and 32.0% respectively. （3） P was the third factor. When pressure changed from 0. 870 × 10^5 to 1. 013 × 10^5 Pa, the difference of contribution could be ignored. In addition, no significant impact was observed on I. Interaction among ions, therefore, could also be ignored. （4） The comparison between previous methods and TECM indicated that results calculated by previous methods were equal to that by TECM with no alkaline neutralization at 298.15 K and 1. 013× 10^5 Pa. TECM considered several environmental factors, thus it is better than previous methods.
出处
《环境化学》
CAS
CSCD
北大核心
2008年第4期416-421,共6页
Environmental Chemistry
基金
国家自然科学基金项目(40573048)
国家重点基础研究973项目(2006CB403205)资助
关键词
酸雨
有机酸
自由酸度
热力学
acid rain, organic acids, free acidity, thermodynamics equilibrium.
