2009年北京市苯系物污染水平和变化特征

POLLUTION LEVEL AND VARIATION OF BTEX IN BEIJING 2009

采用Tenax-TA/吸附热解吸、光离子化气相色谱法(GC-PID)对北京市大气中苯系物(BTEX)的小时平均浓度进行了为期1年的观测.结果表明,苯、甲苯、乙苯、间/对-二甲苯和邻二甲苯的年平均浓度分别为:4.43、7.03、2.27、4.18和2.06μg.m-3.苯系物之间具有很好的同源性,其浓度存在明显的日变化和季节变化,这些变化特征与交通尾气排放、采暖期化石燃料燃烧、光化学反应活性等密切相关.苯与甲苯特征比值(B/T)的分析表明,交通尾气排放是北京市大气中苯系物的主要来源,冬季和早春采暖期化石燃料燃烧也是北京市大气中BTEX的重要来源之一.乙苯与二甲苯比值(E/X)的季节变化为:夏季>春季>秋季>冬季,与北京市大气光化学反应活性季节变化趋势相似.2009年北京夏季总苯系物的平均浓度比2004年夏季减少了2/3,表明北京市政府为改善空气质量所采取的一系列控制措施十分有效.

The hourly averaged concentrations of benzene,toluene,ethylbenzene and xylenes（BTEX） in Beijing were periodically measured during the whole year of 2009.The atmospheric BTEX were pre-concentrated on Tenax-TA tubes,and analyzed by a gas chromatography equipped with a photo-ionization detector（GC-PID） after thermal desorption.Results indicated that the annual averaged concentrations of benzene,toluene,ethylbenzene,m,p-xylene and o-xylene in 2009 were 4.43,7.03,2.27,4.18 and 2.06 μg·m^-3,respectively.BTEX compounds exhibited good same original sources,and their concentrations had distinct diurnal and seasonal variations which were closely relative to vehicle exhaust emission,fossil fuel combustion during heating period and photochemical reactivity.Vehicle exhaust emission was recognized as the major sources for atmospheric BTEX based on analyzing the characteristic ratio of benzene to toluene（B/T）,and the fossil fuel combustion was also one important source for atmospheric BTEX during heating period in winter and early spring.The seasonal variation of the ratio of ethylbenzene to m,p-xylene（E/X,summer〉spring〉autumn〉winter） was in good accordance with the trend of photochemical reactivity in Beijing.The total concentration of BTEX in 2009 summer was lower than that reported in 2004 summer by about a factor of 2.5,indicating that a series of pollution control measures adopted by the Beijing municipal government for improving the air quality are very effective.