Abstract:

At present，acid rain has aroused great concerns of people,but little previous research has been completed on regime shift of acid rain type.Based on the content of SO2-4,NO-3 and SO2-4/NO-3 in the rain of Shanghai,the regime shifts of acid rain type from 1991 to 2006,were studied by adopting the STARS（sequential 〖WTBX〗t〖WTBZ〗test analysis of regime shifts）.There were two regimes of the SO2-4 content;one shift happened in 2004.Before the shift,it was 12.670 mg/L on average;after that,it decreased sharply to 6.525 mg/L.Whereas,there were three regimes,two shifts,of the NO-3 content.Before the first regime shift in 1996,it was 1.842 mg/L on average,after that,it increased to 2.622 mg/L on average till the second shift in 2005,then it decreased again to below 2.000 mg/L on average.Similar to the regime of NO-3 content,there were also three regimes of SO2-4/NO-3,shift twice.Before the first shift in 1995,SO2-4/NO-3 was 7.316;after that,it decreased to 5.666 till the second shift in 2000,then it decreased further to 3.635 on average.These indicated that during 1991～2006 in area of Shanghai,the contribution of NO-3 to acid rain increased,while the contribution of SO2-4 to acid rain decreased.The acid rain types were turning from sulfuric acid rain to sulfuric and nitric acid rain complex type,approaching the nitric acid rain type.Altogether,there were 5 regime shifts of acid rain type during 1991～2006 in area of Shanghai.The regime shift indices (RSI) were 0.826,0.260,0.959，1.378 and 0.066 in 1995,1996,2000,2004 and 2005,accordingly.〖