2012年夏季天津城区BTEX污染特征与臭氧潜势分析

采用AMA GC5000BTX在线色谱仪监测天津城区2012年夏季大气中苯、甲苯、乙苯、邻二甲苯和间-对二甲苯(苯系物,BTEX)的浓度,并结合其最大增量活性因子(MIR)计算各组分的最大臭氧生成潜势量.结果表明,观测期间BTEX浓度均值为38.72μg/m3,其中甲苯和间-对二甲苯浓度最高,乙苯和苯次之,邻二甲苯最低, BTEX存在明显的日变化特征,受大气光化学反应和边界层扩散能力共同影响,午后浓度最低,夜间BTEX浓度维持在较高水平,各BTEX日变化趋势一致.苯与甲苯质量浓度的比值为0.77,表明机动车排放是BTEX的主要来源,但石油化工和涂料挥发等因素也对其存在影响.经计算,间-对二甲苯的最大臭氧生成潜势量最高,甲苯、乙苯和邻二甲苯相当,苯最低, 表明BTEX中间-对二甲苯的光化学反应活性最强.

The diurnal variation and ozone production potential of BTEX in Tianjin in the summer of 2012

The ambient concentration of benzene, toluene, ethylbenzene and xylenes (BTEX) were measured continuously in the urban area of Tianjin from 5th June to 31th July, 2012 by online GC-FID instrument. The ozone formation potential of each component was calculated by the maximum incremental reactivity (MIR) factor. The results showed that the averaged concentration of BTEX was 38.72μg/m3 during the observation period. Concentration of the toluene and xylene were the highest among all components. Ethylbenzene, benzene and o-xylene came next. There was obviously diurnal variations of BTEX concentration. The BTEX concentration which affected by both atmospheric photochemistry reaction and boundary layer diffusion ability was lowest during afternoon and maintained a high level at night. Each species had a consistent daily variation tendency. The high mass concentration ratio of benzene to toluene (0.77) implied that motor vehicle emissions were the main source of BTEX. The factors of oil and chemical coating volatile had also influence. Maximum incremental reactivity (MIR) was used to calculate the largest ozone formation potentials of benzene, toluene, ethyl benzene and xylene. The m/p-xylene had the largest ozone formation potentials. The ethyl benzene and o-xylene were at same level. The benzene had lowest potential. This result showed that the m/p-xylene had the strongest photochemical reaction activity among all components of BTEX.