Background concentrations of reactive gases and the impacts of long-range transport at the Jinsha regional atmospheric background station

Lorentz curve fittings are applied to frequency distributions of the concentrations of O3, CO, NOx and SO2 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 100m 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 O3, SO〉 NOx 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 O3 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 SO2, CO and NOx 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 NO3 concentrations, lower relative humidity, and higher concentrations of O3 and SO2.

Emission inventory evaluation using observations of regional atmospheric background stations of China

Any accurate simulation of regional air quality by numerical models entails accurate and up-to-date emissions data for that region.The INTEX-B2006 （I06）,one of the newest emission inventories recently popularly used in China and East Asia,has been assessed using the Community Multiscale Air Quality model and observations from regional atmospheric background stations of China.Comparisons of the model results with the observations for the species SO2,NO 2,O 3 and CO from the three regional atmospheric background stations of Shangdianzi,Longfengshan and Linan show that the model can basically capture the temporal characteristics of observations such as the monthly,seasonal and diurnal variance trends.Compared to the other three species,the simulated CO values were grossly underestimated by about two-third or one-half of the observed values,related to the uncertainty in CO emissions.Compared to the other two stations,Shangdianzi had poorer simulations,especially for SO2 and CO,which partly resulted from the site location close to local emission sources from the Beijing area;and the regional inventory used was not capable of capturing the influencing factors of strong regional sources on stations.Generally,the fact that summer gave poor simulation,especially for SO2 and O 3,might partly relate to poor simulations of meteorological fields such as temperature and wind.