The Study On Concentration Levels And Changes Of BTEX In Beijing

BTEX is important pollutant from anthropogenic emissions, BTEX in the urban atmosphere has the serious influence to the region and local distant. First, BTEX has effect on the humanity respiratory system, the hemopoietic tissue system, the nervous system. Benzene also has the strong carcinogenicity. Next, BTEX is active in the photochemical reactions. and thus influence the ozone formation as well well the second organic aerosol formation. Therefore, many developed countries (for example the US, Europe and Canada and so on) take BTEX in the atmosphere as the routine monitoring content, and has stipulated its strict air quality standard. Researchers in our country have also conducted some research to the urban atmosphere, but these research mainly concentrate on photochemical reaction-active period (June to August). BTEX concentration level during the whole year and the characteristic in city atmosphere are seldome reported. Therefore, a one year atmospheric BTEX investigation has been carried out in Beijing in 2009, to know the BTEX pollution level, the characteristic as well as the origin.The hourly concentrations of Benzene, Toluene, Ethyl benzene and Xylene (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 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 and fossil fuel combustion during heating period were recognized as the major sources for atmospheric BTEX based on analyzing the characteristic ratio of benzene to toluene (B/T). The seasonal variation character 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 average concentrations of benzene, toluene, ethylbenzene, m,p-Xylene and o-xylene for the whole year were respectively, about a factor of 5 lower than the reported values in 2001, indicating that a series of control measures adopted by Chinese government for improving the air quality in Beijing are very effective.