Research On Acid Rain Chemical Characteristics And Acid-cause Substances Transport

To find out the sources of acid substances is meaningful for the control of acid rain pollu-tion. In this study, analysis of one city precipitation chemical characteristics of precipitation has been carried on based on the monitoring data of2006to2010from the Environmental Monitor-ing Station of this city. Meanwhile, we invetigated the emission sources of SO2in50km circular region to find the relationship between the pollutant sources and acid rain, then we uesd decision tree to find the impact of meteorology on the formation of acid rain.Finally, back-trajectory model HYSPLIT and cluster analysis were used to analyze the chemical characteristics of72h backwards trajectory at three different heights. The main conclusions are as follows:(1) The pH of precipitation in the city declined from2006to2010, and the frequency of ac-id rain trended to increase. The ratios of sulfate and nitrate molar concentration in five-year acid rain were1.31,1.49,1.28,0.99and1.25. The acid rain belonged to the mixed acid rain, sulfuric was the main acid-causing factor, the ratio of the concentration of sulfate and nitrate fluctuated little. The total ion concentration decreased after increase from2006to2010, which was384.04μeq/l in2010. Precipitation ion concentrations on the wind direction to the southwest and southeast were the highest, southwest to487.89μeq/L, southeast to480.49μeq/L.(2) The meteorological data in2010of this city was analyzed to find the relationship be-tween the wind direction and pollutant emission. In2010, the frequencies of the northeast, east and northeast east are higher, whose values are11.16%,10.89%and10.75%. The emission from the east was also the highest, which may increase the possibility of acid rain pollution in this city.The acid rain prediction accuracy rate of decision tree was70.49%. The prediction accuracy rate of "acid rain" and "non-acid rain" were59.24%and83.97%. The results showed wind speed had the greatest impact on the formation of acid rain, whose importance was0.589, followed by relative humidity, temperature and precipitation. It is quite possible that the distribution of pollu-tant sources and long-range transport have an great impact on the formation of acid rain. (3) In the years of2006to2010, back-trajectories at the height of100and500meters are mainly from the east. These rainy days had a higher acid rain frequency. Trajectories at the height of1500and3000meters are mainly from the west. The days whose trajectories are short-er have a heavier acid rain pollution. At the height of3000meters, the days whose trajectories length is under1000kilometers have a lower pH, which shows an obvious impact from middle and short distances.After comparing the difference of trajectories in acid rain and non-acid rain days, it was found that the southeast and northeast trajectories have a higher occurrence frequency at the height of100meters; at the height of500meters, the frequency of northeast trajectories in acid rain days is more higher; at the height of1500meters, the difference is not very obvious; at the height of3000m, the frequency of south trajectories in acid rain days is more higher.After comparing the back-trajectories in this city with the other two cities, the difference was found at the height of500and3000meters, it has a greater impact by the northeast trajecto-ries at the height of500meters, it has a greater impact by the southwest trajectories at the height of3000meters.