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2010年1月、4月、7月和10月在市区4个点(省政府大楼、泸灞生态区、微电机厂、地环所)利用低流量采样器各分别采集2周的PM,.样品(24h),使用DRIModel2001热光碳分析仪分析其有机碳(OC)和元素碳(Ec)浓度.结果表明,西安PM2.5.年均浓度为167.2±11.7μg·153-3,达到国家最新PM2.5.年均标准(GB3095-2012:35μg·m-3)的5倍左右.空间上,采样点靠近城市中心区域(古城墙)越近.PM2.5;的含量越大;季节上呈现冬高夏低.4个采样点中ECl,EC2和EC3的百分含量曲线重合表明EC来源一致(源排放燃煤),而OCl,OC2,OC3和OC4峰值不一致表明OC来源多样,这一点也得到了OC和EC的良好相关性以及与气态污染物SO2和NO2相关性的验证.将OC与EC的观测数据与前人研究的年际数据和国内外代表性城市数据对比,OC/PM2.5;比例减少,而EC/PM2.5,比例却保持在5%左右,表明PM2.5,组分中含碳组分比例在下降.采用OC/EC最小比值法估算SOC的含量和百分比分别为11.9μg·m-3和54.6%. “,”PM2.5 mass and chemical compositions of the quartz-fiber filter by Minival samplers were measured in Xi'an for two weeks of every month from January, April, July and October during 2010 at four urban sites (Sheng zhengfu, Chanba, Wei dianji, Institute of earth environment). Organic (OC) and elemental carbon (EC) were determined by thermaL/optical carbon analyzer DRI Model 2001. Annual average PM2.5 concentrations were 167.2± 11.7 μg·m-3, which is 5 times than the latest national ambient air quality standard of China in 2012 (35 μg·m-3). PM2.5 concentrations varied with distance close to downtown spatially and theirs seasonal patterns were “low level in winter and high in summer”. Distribution patterns of EC1, EC2 and EC3 in total carbon (TC) indicated that the dominant EC emission sources was similar, but inconsistent peak values for OC1, OC2, OC3 and OC4 in TC implied diverse OC sources. This is also confirmed by the good correlations among OC, EC, SO2 and NO2. Comparison of interannual observation data showed the decreasing ratios of OC/PM2.5 and constant EC/PM2.5 ( -5% ) at Xi'an, which indicated that carbonaceous component of PM2.s reduced in the last several years. SOC (secondary organic carbon ) content and percentage in OC were estimated to 11.9 μg·m-3 and 54.6%, respectively, using minimum OC/EC ratio method.