Characteristics of acid rain and its forming reason from 2003 to 2007 in Rizhao, Shandong province

Based on the acid rain observation data and the related meteorological data from 2003 to 2007 in Rizhao, annual, seasonal and monthly variations of precipitation pH were analyzed. The change characteristics of acid rain and its forming reason were discussed. The results indicate that the frequency of acid rain is about 20%. The lowest pH value of precipitation is 4.37, and it belongs to the stronger acid rain. The highest pH value of precipitation is 7.12. The annual average values take on the descending trend, and pH value decreases gradually. The frequency of acid rain is the highest in winter, followed in spring, summer and autumn. The monthly changes also display some certain rules. The monthly average exceeds the standard of acid rain. Under the ESE wind direction, stable cloud system and light fog weather conditions, acid rain occurs easily. Acid rain weather is related to local topography, industry layout, outside source, natural source and so on.