Characterization of volatile organic compounds in the urban area of Beijing from 2000 to 2007

Beijing is one of the most polluted cities in the world.In this study,the long-term and continuous measurements of volatile organic compounds （VOCs） in the urban area of Beijing,specifically at Beijing 325 m Meteorological Tower,were conducted from 2000 to 2007.The annual record of VOC trends exhibited in two different phases was separated in 2003.Records show that VOC concentrations increased from 2000 to 2003 due to the abrupt increase in vehicle number.Contrarily,since 2003,there had been a decrease in VOCs concentrations as the policy on gasoline and air pollution was implemented.Toluene,benzene,and i-pentane are the chemicals that abound in and are directly related to vehicle activity,such as in vehicle exhaust and gasoline evaporation.Furthermore,records indicate that there had been seasonal variation in VOCs levels in that VOCs level in summer is higher than that in winter.As such,temperature is considered to significantly contribute to VOCs in Beijing.Records also show that VOCs level was high in the morning and during rush hours in the evening.In contrast,VOCs level was low during midday due to photochemical destruction with OH radical and dilution effect.In this study,a particular benzene to toluene ratio range （0.4–1.0） was used as the indicator of air propelled by vehicular exhaust.We also applied the correlation coefficients between BTEX and i-pentane to evaluate evaporation influence to ambient BTEX in the Beijing urban area.