南充市近十年酸雨变化特征及降水化学组成研究

依据南充市2003~2012年城区降水环境监测统计资料,分析了酸雨变化特征及降水离子化学组成。研究表明:这十年,酸雨频率平均为50.4%,2007年降雨量为最高,呈波动递减趋势变化,降水年平均pH值为4.88,呈现"低—高—低"的变化特征,城区酸雨频率和降水pH值月均值变化呈现高低交替的波动趋势。城区降水中主要阳离子成分是Ca2+,主要阴离子成分是SO2-4和NO-3。(SO2-4/NO-3)比值逐年下降,平均比值为7.82,酸雨污染类型仍以硫酸型为主;降水(NH+4+Ca2+)/(SO2-4+NO-3)和Ca2+/NH+4比值呈波动性变化,2007年分别达到最高值为6.71和50.27,除2010年比值均较低小于1外,近年来均有增加趋势,表明碱性离子缓冲能力增强了,降水酸度降低,pH值增加,但2007年pH值较低,主要与降雨量有关。综合分析,降水酸度不仅是酸性离子和碱性离子中和作用,也受其他离子浓度和降雨量、风向等气候条件、距离传输以及地形等影响。

Study on Changing Characteristics of Acid Rain and Chemistry Composition of Rain Water in Nanchong in Recent Decade

Based on the local precipitation environmental monitoring data from 2003 to 2012,this paper analyzed the changing characteristics of acid rain and chemical compositions of rainwater in Nanchong urban area,the research indicated that the frequency of acid rain was 50.4％ on average in recent ten years,precipitation was the highest in 2007,and decreased with fluctuation change.The annual average pH value of the precipitation was 4.88,and presented ＂low-high-low＂ pattern.The acid rain frequency and pH average value of precipitation in the urban area presented high and low alternating fluctuation pattern.The major cation in the precipitation was Ca2 ＋,the main anions were SO42-and NO3-.（SO42-/NO3-） ratio decreased year by year.The average ratio was 7.82 and the main pollution type of acid rain was sulfate.（NH4＋ ＋ Ca2＋） / （SO42-＋ NO3-） and Ca2 ＋ /NH4＋ ratio of precipitation showed a fluctuation trend,reached the highest value 6.71 and 50.27 respectively in 2007.The ratio values showed an increasing trend in recent years except that in 2010 the ratios were all lower than 1,indicated that the buffer capacity of basic ion had enhanced,the acidity of precipitation decreased and pH values increased,However,in 2007,pH was low,mainly related to rain capacity.Comprehensively analysis,the acidity of precipitation is not only neutralization of acidic ionic and basic ion,but also is affected by the concentration of other ions,rain capacity,wind direction and other weather conditions,transmission distance and topographic.