西安大气环境要素变化特征分析

利用1951年至2007年西安气象观测资料及2002年至2007年环境监测资料，对西安市大气环境要素进行分析。结果表明，（1）随着西安城市化进程的加快，和NOx年平均浓度变化具有明显增加的趋势。（2）从1951到2007，西安市气温增长了约2℃，仅21世纪以来，就增长了近1℃。热夜天数自上世纪90年代中期以来明显上升。2008年7月上旬西安市区与周边郊区地表温度温差约为8—10℃。（3）年平均风速，极大风速明显减小。分析认为，随着西安城市规模的扩大、人口的增加，高楼林立，城市下垫面发生巨大变化，使城市热容量增加，耗能增大，有效蒸发减少，增温明显，从而导致城市风速减小、大气污染物浓度增加、温度升高、热岛效应越来越显著。提出建立人工环境与自然环境协调一致的城市规划环境气候图，有效缓解因城市化进程引起的城市大气环境问题。

STUDY ON THE VARIATIONS OF ATMOSPHERIC ENVIRONMENTAL ELEMENTS IN XIAN

Based on the meteorological data from 1951 to 2007 and atmospheric environmental data from 2002 to 2007 in Xi＇an city, the variation characteristics of atmospheric environmental elements were analyzed. The results showed that： （ 1 ） With the accelerated process of urbanization, the variations of annual average concentration of SO2 and NOx showed a clear upward trend. （2） From 1951 to 2007, the temperature increased by about 2℃. It increased by nearly 1℃ only in the 21st century. Since the mid -90s of last century, number of hot nights increased obviously. The surface temperature difference between city zone and surrounding suburbs was about 8 to 10℃. （3） The annual average wind speed and maximum wind speed significantly reduced. According to analysis, with the city＇s expansion, population increase, tall buildings may be built frequently and underlying surface may change dramatically. That may lead to the increase of the urban heat capacity, the energy use and the temperature, and the reduction of the effective evaporation. Consequently, the urban wind speed decreases, the concentration of air pollutants increases, the temperature increases, and the heat island effect becomes increasingly evident. Accordingly, it is suggested to make an urban environment and climate map that can make the artificial environment harmonized with the natural environment when we when we do urban planning. So, the urban air environmental problems caused by the process of urbanization can be effectively mitigated.