• 关键词：北京  降水  pH值  湿沉降

• 基金项目：国家“985工程”专项资助(No.CUN985-3-3)

• 李令军
• 北京市环境保护监测中心, 北京 100048

• 王英
• 中央民族大学生命与环境学院, 北京 100081

• 徐谦
• 北京市环境保护监测中心, 北京 100048

• 王文盛
• 北京市环境保护监测中心, 北京 100048

• 金蕾
• 北京市环境保护监测中心, 北京 100048

• 鹿海峰
• 北京市环境保护监测中心, 北京 100048

• 林安国
• 北京市环境保护监测中心, 北京 100048

• 摘要：分析了2008年8月奥运期间北京大气降水的理化特征,并与往年同期的降水特征进行了比较,进而深入研究了北京1997～2008年大气降水酸化趋势及湿沉降变化.研究结果发现:北京奥运期间大气污染控制措施的实施改善了北京的空气质量,并影响了降水离子构成;地壳源排放的减少降低了大气降水酸化缓冲能力,降水中Ca²⁺离子浓度比例降低,大气降水明显酸化;与往年相比,2008年8月北京大气降水表现为全市区域酸化趋势,湿沉降量也明显增加,这与北京近地面环境空气质量明显改善并不一致.此外,监测数据统计显示:近10年来北京空气质量的改善并没有降低北京大气降水湿沉降量,而且北京降水离子构成异于近地面主要大气污染物PM₁₀.因此,近地面大气污染直接排放可能并不是北京降水湿沉降的唯一来源.夏季北京降水以偏南气流为主,而且存在由南向北的大气污染输送层,外来污染输送及区域性大气污染汇聚成为北京大气降水湿沉降的重要来源,但是否为北京大气降水湿沉降的主要来源需进一步研究证实.

• Abstract：Acid precipitation and wet deposition in Beijing for 1997～2008 were studied by comparison of the physical and chemical properties of precipitation samples collected during the 2008 Olympics with precipitation samples collected previously. The results showed that the air pollution control measures implemented during the Beijing Olympics indeed improved the air quality of Beijing and also modified the composition of the precipitation. Reduced emission of crustal-originated materials weakened the buffering effects; the Ca²⁺ ion concentration in precipitation decreased,which significantly intensified the acidity of the precipitation. Compared to precipitation acidity and atmospheric quality of previous years,precipitation in Beijing in August 2008 showed observable acidification and increased wet deposition,which was not in agreement with the improved ambient air quality. Monitoring results indicate that,in recent decades,the improvement of air quality in Beijing has not reduced the amount of wet deposition. The ionic composition of the precipitation in August 2008 was different from that of the main atmospheric pollutants PM₁₀. Therefore,local pollution emission may not be the main source of wet deposition in Beijing. Summer precipitation in Beijing was mainly due to southerly airflow. The south-north air pollution transport layer may be the major source of Beijing's wet deposition. In conclusion,external contamination and convergence of regional air pollutants could be important sources for the wet deposition in Beijing. However,more evidence is necessary to elucidate whether these factors play a key role in the occurrence of wet deposition of atmospheric precipitation in Beijing.

• Key words：Beijing  precipitation  pH  wet deposition

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