Diurnal and seasonal variation of BTEX in the air of Monterrey, Mexico: preliminary study of sources and photochemical ozone pollution

Atmospheric levels of benzene, toluene, ethylbenzene, and xylenes (BTEX) were measured in an urban site located in Nuevo Leon, Mexico, during summer and autumn 2013. A total of 60 samples were collected using carbon-packed cartridges at 0900, 1200, and 1500 h and then analyzed using gas chromatography with flame ionization detector. Meterological parameters and criteria air pollutants were measured and correlated with BTEX by a principal component analysis (PCA). The relative abundance of BTEX followed the order: benzene > toluene > ethylbenzene > p-xylene with mean concentrations of 55.24 μg m−3, 22.24 μg m−3, 6.94 μg m−3, and 4.17 μg m−3, respectively, during summer. Mean concentrations during autumn were 21.079 μg m−3 for benzene, 3.648 μg m−3 for toluene, 2.521 μg m−3 for ethylbenzene, and 2.115 μg m−3 for p-xylene. All measured BTEX showed clear diurnal and seasonal patterns. The highest mean levels for benzene were obtained during the midday. Toluene, ethylbenzene, and p-xylene showed the highest levels during afternoon period. BTEX levels were higher when wind blew from NE and ESE during summer and from ESE during autumn. The municipalities of Apodaca and Guadalupe are located in these directions where important industries, high traffic volume, many oil and gas service stations, and the biggest airport in this region are found. These sources could contribute to the BTEX concentrations measured during the sampling period