The Features Of Spatial-temporal Distribution And Study On Prediction Methods Of Acidrain In Nanning

This thesis gives an analysis on the features of spatial-temporal continuum distribution of acidrain in the region of Nanning according to the monitoring data from 1991 to 2004 about pH value, SO₄^2-,NO₃^-,F^-,Cl^-,NH₄⁺,Ca²⁺,Mg²⁺,Na⁺ and K⁺ in the region. A further statistical analysis is made about the relationship between pH value and meteorological conditions as well as the influence of weather prognostic field on the change of pH value with the help of the data about baric topography of the corresponding period,and synoptic chart and meteorological parameter in atmospheric boundary layer,which accounts for the regular pattern of the change of pH value,based on which primary predictors chosen from former meteorological and pollute data are contracted as synthesized ones by using EOF (empirical orthogonal function) decomposition. The synthesized predictors which are closely related to the predictands mentioned above and contributed to them mainly are selected to build statistical prediction equations respective season. Finally,a comparative study is carried out on the advantages and disadvantages of statistical prediction model of EOF and progressive regression.The above analysis shows that the acidrain is more serious in winter and spring than in fall and summer and the dominant ion of precipitation is SO₄^2- and NH₄⁴⁺. The value of SO₄^2- /NO₃^- is 6.97. There is one peak time in Monthly change (the greatest value in February,the lower in May). The harm of acidrain is more serious in suburb than in city, and becomes severe along the dominating direction of wind in city. A further analysis indicate that the acidrain of Nanning is not anly affected by native pollution, maily affected by external pollution sources from the industries and enterprises in Xiang-gui corridor. In spring ,fall and winter, the wind direction is north ,but in summer is east with the acidrain. The wind velocity is in direct proportion to the frequency of acidrain, and the pH value is in inverse proportion to rainfall pollution. The thicker inversion layer is, the greater the acidrain is. The thinner mixed layer is ,the greater the acidrain is and winter sees the thinnest mixed layer of a year in Nanning. Among the six types of circulations resulting in the Nanning acidrain , the upper trough -cold front is the major one,which brings the most seriousacidrain and the quality of rainfall becomes good when the typhoon affects.By the way of making EOF with the predictors in order to decompose and eliminate correlation oneselves, the synthesized predictors which are closely related to the predictands mentioned above and contributed mainly are selected to build statistical prediction equations. The result indicates that the model performs better than progressive regression model on the pH value forecast.