Aircraft measurements of BTEX compounds around Beijing city

A high sensitive method has been developed for measuring atmospheric BTEX (Benzene, Toluene, Ethylbenzene, Xylenes) by using Gas Chromatography equipped with Photo-Ionization Detector (GC–PID). The Method Detection Limits (MDLs) were: Benzene 0.66 ng m−3, Toluene 2.03 ng m−3, Ethylbenzene 5.91 ng m−3, m,p-Xylene 6.49 ng m−3 and o-Xylene 5.45 ng m−3. Vertical distribution of BTEX from ground level to 3600 m around Beijing city was measured during flight of aircraft in July and November, 2011. Remarkable decrease of each BTEX species with increasing height was observed, and the sum concentration of BTEX decreased from 21.7 μg m−3 at ground level to 0.19 μg m−3 at height of 3600 m. The ratio of benzene to toluene (B/T) also increased pronouncedly with increasing altitude, but became flat above 1800 m. The vertical distribution characters of BTEX and B/T were ascribed to diffusion and photochemical consumption of BTEX.