THE EFFECTS OF BELOW-CLOUD AEROSOL ON THE ACIDIFICATION PROCESS OF RAIN

Using a model of the acidification process of rain, we calculate and a nalyze the effects and contributions of a below-cloud aerosol in its d ifferent concentrations and acidities on the pH and ion components of rain (SO42-, H+, NO3-, NH4+, etc.) under the conditions of different c oncentrations of pollution gases. The results show that the aerosol ha s an acidification or alkalization effect on the rain which changes th e pHs of rain and aerosol. As acidifying pollution gas concentrations (SO2, HNO3) are low, the acid aerosol has important effects on the pH and H+ of rain, but as the gas concentrations are high, the acid aeros ol has very little effect. The alkalizing aerosol makes the pH of rain increase by between 0.3 and 0.5 and neutralizes about 60% of H+ in th e rain. As alkalizing pollution gas NH3 exists, the acid aerosol has i mportant effects on the pH and H+ of rain. But the alkalizing aerosol has very little effect, especially as the NH3 concentration is high. T he percentage contribution of the aerosol to SO42- in rain is generall y 7-15%, the contribution of the aerosol to NO3- is nearly the same as that of HNO3 = 1 ppb, and the contribution of the aerosol to NH+ is n early the same as that of NH3, from 5 to 7 ppb, and is an important so urce of NH4+ in rain. Finally, according to the actual conditions of t ypical regions in the south and north of China (Chongqing and Beijing) , we analyze the effects of aerosol and pollution gases on the ion com ponents of rain.