Chemical Characteristics Of Cloud And Precipitation At Mount Heng

Since acid rain was observed for the first time, it has been studied over the world. Because the acidification of cloud and fog was also thought to be the significant reason causing acid rain, atmospheric chemistry about cloud and precipitation was conducted at Mount Heng in order to get an overview of the transformation of acidic pollutant and acid rain formation in China. Because of special topography and location of this site, by this study it was of great benefit to understand the chemical characteristics of air pollution and source and transport of these pollutants.A total of 193 cloud/fog samples and 38 precipitation samples were collected during Mar.2009- May 2009 at the summit of Mt. Heng in order to examine the impact of regional sources of pollution on cloud and fog water chemistry in the highly affected by acid rain. All samples were analyzed for electric conductivity (EC), pH, F-, CF,NO3-, SO42-, NH4+, K+, Na+, Ca2+, Mg2+ and organic acids to study chemical Characteristics of the cloud and precipitation at this region.The cloud/fog water was acidic with the volume weighted mean (VWM) pH 3.80 and about 76% of samples could be identified as strongly acidified cloud. The cloud water on Mount Heng was relatively acidic compared with the monitoring results on some other rural high elevation sites on global, indicating strongly anthropogenic emission and frequently dust activities in the East Asian. The cloudwater had a relatively high ion concentration (1143.25μeqL-1). In general the predominant ions in cloudwater collected over the world were sulfate, nitrate, ammonium and calcium, but this study found that besides these ions, the cloudwater in this site contain a rather high concentration of sodium ion, indicating this site was affected by air masses from the sea in this season. In addition the ratio of low-mole organic acids in this study was rather high and the contributions of these carboxylic acids reach to 3.52%. Compared with the monitoring data twenty years ago, cloudwater in this site became more acidic and the total concentrations went a bit higher. In more specific terms, compared with the former, alkaline ions kept constant, and yet a different situation appeared about acidic ions and the concentrations of these acidic ions rose.About 65% of precipitation events were acidic with the VWM pH 4.35 and the corresponding ionic concentration up to 243.3lμeqL-1. Same as the cloudwater, ammonium and calcium were the predominant cations in precipitation which were affected by human activities, sandstorm and alkaline particulates. Meanwhile the same situation appeared about anion in precipitation and sulfate and nitrate were the dominant anions with the ratio to the total content 29.2%,11% respectively, which were mainly from non-sea sources. The concentrations of carboxylic acids in precipitation were rather high with formic and acetic acids dominating, which were related with the subtropical climate Mount Heng located. Compared with the former monitoring data about precipitation, the acidity of precipitation in this study kept stable and the total concentration dropped a little.Because of different washout effect of cloud and rain droplets on acid gases and particulate matter in the atmosphere, different ions appeared different ratios in cloud and precipitation and ammonium, nitrate and sulfate showed higher ratios in cloudwater with the calcium ion higher ratio in precipitation. The correlation coefficient of major ions between cloud and precipitation listed from-0.35 to 0.47, and these results showed no obvious correlationships existed between cloud and precipitation, suggesting that the rain formed from a different cloud from the one that was sampled.The reason why most of cloud and precipitation events in this study showed strong acidic was that there were a large number of acids not being neutralized. And the ratios of non-neutralized acid in cloud and precipitation were 28% and 35% respectively. Sulfate, nitrate and organic acids were considered to be the significant contributors to the acidity of cloud and precipitation. Ammonium and calcium were main neutralized factors.Cloud events caused by air masses from Southern China and East China appeared higher acidity and more ionic concentrations, which was caused by that these two cluster air masses passed by most industrialized regions in China and were polluted strongly by anthropogenic sources. Cloud events associated with airmasses from southwest and local airmasses generally showed higher pH values and low ion concentrations. The pH values of rain events associated with airmasses from South China, East China, North China, southwest and local environment were 4.22,3.98, 4.48,4.66 and 4.56 respectively. Air masses from East China and North China carried a large number of ion to precipitation, while precipitations associated with local atmosphere and southwest airmassed were rather clean.By enrichment factor analysis, most of sulfate, nitrate, potassium and calcium and a some proportion of magnesium came from the non-sea sources with most of potassium and calcium contributed by crust and soil. The formate to acetate ratio in cloudwater was 1.23 and somewhat higher compared with the corresponding value in precipitation (0.87), suggesting that organic acids in precipitation mostly came from direct emissions, while apart from direct sources, secondary transfer from related precursors affected the concentration levels of organic acids in cloud to a greater extent compared with that did in precipitation.In sum, in this study these were found that compared with previous monitoring data, now precipitation did not become acidic and acidic species in it originated from anthropogenic emissions in Pearl River Delta and Yangtze River Delta regions. These results would help us to realize pollutant sources in this ares and control acid rain.