| 1 | Background concentrations of reactive gases and the impacts of long-range transport at the Jinsha regional atmospheric background station显示文摘Lorentz curve fittings are applied to frequency distributions of the concentrations of O 3 , CO, NO x and SO 2 recorded at the Jinsha regional atmospheric background station (JSH) from June 2006 to July 2007, and the peak concentrations of these species for the different seasons are obtained. The peak concentrations are considered to be representative of different background levels for certain processes. The peak concentrations are compared with the corresponding mean (median) concentrations, and the suitability and limitations of the mean (median) values as the background levels are discussed. The mean (median) values might represent the background concentrations in the region under some circumstances, but in other cases these values often underestimate or overestimate the true background concentrations owing to the transport of pollutants and other factors. The effects of air masses transported from different regions on the pollutant background concentrations are obtained by analyzing the 72-hour backward trajectories of air masses 100 m above the ground at JSH. These trajectories are estimated using the HYSPLIT model and then clustered for the measurement period. The spatial distribution and seasonal variations of trajectories and the corresponding mean concentrations of O 3 , SO 2 , NO x and CO for different clusters are analyzed. After filtering the seasonal changes in pollutant concentrations, the relative influences of air masses from different regions are obtained. The results show that JSH can be used to obtain the atmospheric background information of different air masses originating from or passing over the Yangtze River Delta, Central South China and the Jianghan Plain. Air masses from Central China, South China, and the western Yangtze River Delta contribute significantly to O 3 at JSH. Air masses from the north and northeast of JSH (i.e., the Jianghan Plain, Huang-Huai Plain and North China Plain) and the south (Central South China) contribute significantly to SO 2 , CO and NO x concentrations. Air masses originating from the ocean often bring clean air. Air masses originating from high altitudes over northwestern regions often have lower CO and NO x concentrations, lower relative humidity, and higher concentrations of O 3 and SO 2 . | LIN WeiLi XU XiaoBin SUN JunYing LIUXiWen WANG Ying | 2011 | Science China Earth Sciences2011，54，10： | 8 |
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