珠江三角洲城市雨水的化学组成及其成因探讨

于2005—2007年间,基于降水过程监测分析了广州市和珠海市雨水的化学组成。结果表明,广州市雨水的pH值变化于3.32~7.03之间,平均值为4.35,众数约为4.15。珠海市雨水的pH值变化于3.38~6.49之间,平均值为4.51。雨水pH值随降水强度的减弱而降低,这决定于大气中水汽与酸性气体的接触时间。珠江三角洲城市雨水中所含主要离子依次是SO42-、NO3-、NH4＋、Ca2＋、Cl-。雨水的酸化与降水过程密切相关。降雨初期雨水比中后期雨水的pH值高,揭示降雨初期大气中的粉尘颗粒有效中和雨水的酸度。多天连续降水天气对大气尘埃的清洗作用明显,但是持续的SO2和NOx排放更容易使雨水酸化。滨海城市降水初期雨水的电导率上升较快（可以从小于1μS.cm-1上升到20~30μS.cm-1）,随着降水时间的延长雨水的电导率以较慢的速率上升。

Chemical composition and its origin of urban rainwater in the Pearl River Delta

Based on the precipitation processes,observation and physiochemical analysis of the rainwater had been carried out in Guangzhou and Zhuhai cities from 2005 to 2007.The results demonstrated that pH values of rainwater in Guangzhou City changed from 3.32 to 7.03 and averaged at 4.35 with the mode at 4.15.The pH values of rainwater changed from 3.38 to 6.49 and averaged at 4.51 for Zhuhai City.The pH values of rainwater which is the function of the duration of interaction between water vapor with the acidic gases decrease with decreasing rainfall intensity.The major ions contained in rainwater of the Pearl Delta are SO42-and NO3-,followed by NH4＋,Ca2＋,and Cl-.Acidification of rainwater is closely related to the precipitation processes.The pH value of rainwater is higher in the initial stage of precipitation than those in the middle and later stages of precipitation,indicating that the dusts in the atmosphere partly neutralized the acidity of the rainwater at the initial stage of the precipitation.Under the continuous multiple days raining weather,it is much easier to acidify the rainwater in the city with the persistent emission of SO2 and NOx.The electricity conductivity of rainwater increased rapidly in the initial contact of the fresh vapor from the sea with the acidic gases in coastal city,e.g.,changed from less 1 μS cm-1 up to 20-30 μS cm-1 in a half hour,subsequently,the electricity conductivity of rainwater kept increasing with a slower rate.