天津城区夏冬季典型污染过程中BTEX变化特征及其健康风险评估

利用GC955在线气相色谱仪分别于2019年7月和2020年1月在天津市区开展苯系物（BTEX，包括苯、甲苯、乙苯、间/对-二甲苯和邻-二甲苯）实时在线观测，对典型污染过程中BTEX的浓度水平、组成及演化机制进行了研究，并运用特征物种比值法对BTEX的来源进行了定性分析，最后运用US EPA的人体暴露分析评价方法对BTEX健康风险进行评估.结果表明，臭氧和霾污染过程中BTEX体积分数平均值分别为1.32×10^-9和4.83×10^-9，其中苯的体积分数占比最大，其次是甲苯、乙苯和二甲苯占比最小.2020年1月BTEX体积分数很大程度上受到西南方向短距离传输的影响，而在2019年7月BTEX浓度受到本地排放的影响.BTEX浓度水平在2019年7月受到温度和相对湿度的共同影响，而在2020年1月当温度较低时BTEX浓度对相对湿度的变化更敏感.天津市区BTEX在霾污染过程中受生物质燃烧/化石燃料燃烧/燃煤排放的影响较大，而在臭氧污染过程中除了受到燃烧排放源影响，交通源排放在很大程度上也有影响.臭氧污染和霾污染过程中BTEX的HI分别为0.072和0.29，均处于EPA认定的安全范围内.苯的致癌风险在清洁天和污染过程中均高于EPA规定的安全阈值，需引起高度重视.

Characteristics of BTEX and Health Risk Assessment During Typical Pollution Episodes in Summer and Winter in Tianjin Urban Area

Real-time BTEX(including benzene, toluene, ethylbenzene, m-, p-, and o-xylenes) were measured continuously in Tianjin urban site in July 2019 and January 2020 using a Syntech Spectras GC955 analyzer. The BTEX concentration levels, composition, and evolutionary mechanisms during typical pollution episodes were investigated. The potential sources of BTEX were analyzed qualitatively using the diagnostic ratios method. Finally, the BTEX health risk was evaluated by using the human exposure analysis and evaluation method according to US EPA. The averaged total mixing ratio of BTEX were 1.32×10^-9 and 4.83×10^-9 during ozone pollution and haze episodes, respectively. Benzene was the most abundant species, followed by toluene. The mixing ratio of BTEX was largely affected by short southwestern distance transportation in January, while local emissions in July. In addition, the BTEX mixing ratio depended on the influence of temperature and relative humidity(RH) in July, while the concentration was more sensitive to changes in RH when the temperature was low in January. Diagnostic ratios and source implications suggested that the BTEX was affected mainly by biomass/biofuel/coal burning during haze episodes. The traffic related emissions also had an impact except for the influence of biomass/biofuel/coal burning in July. The averaged hazard quotient(HQ) values were 0.072 and 0.29 during ozone pollution and haze episodes, respectively, which were in the upper safety range limit recommended by the US EPA. The carcinogenic risk posed by benzene in both cleaning and pollution processes was higher than the safety threshold set by the US EPA, which should be monitored carefully.