基于后向轨迹对城市大气中二噁英长距离迁移来源的探讨

通过对广州某商住区大气中二噁英的季节性监测,结合后向轨迹的计算,对大气中PCDD/Fs的浓度及其长距离迁移来源进行分析.结果表明:大气中二噁英浓度有季节性变化特点,其趋势为冬季(14.4 pg·m^-3)>秋季(10.0 pg·m^-3)>春季(5.54 pg·m^-3)>夏季(3.88 pg·m^-3).同时,大气中PCDD/Fs单体特征也具有季节性特点,秋冬季节七氯代、八氯代PCDD/Fs百分比高于春秋两季,春夏两季低氯代单体百分比含量高于秋冬两季.追溯采样期间该城市大气的后向轨迹,发现秋冬两季到达广州的气团主要经过湖南、湖北和江西等北方或东北方的内陆省份,而春夏两季到达广州的气团主要经过我国东海和南海海域上空.而这种变化很可能是造成广州大气中二噁英浓度季节性变化的主要原因.

Long-range transport source of dioxin in the urban atmosphere based on backward trajectories

Atmospheric concentrations of 2,3,7,8-PCDD/Fs were measured seasonally in a hybrid area of commerce and residence of the Guangzhou city. The average concentrations of PCDD/Fs in the atmosphere decreased as: winter (14.4 pg·m^-3) > autumn (10.0 pg·m^-3) > spring (5.54 pg·m^-3) > summer (3.88 pg·m^-3). Seasonal variation was also observed for the congener distribution. Air samples collected in autumn and winter contained higher abundance of hepta- and octa-PCDD/Fs than those in spring and summer, whereas the contribution of low chlorinated PCDD/Fs increased in spring and summer samples. Backward trajectories analysis showed that air masses were mainly from inland provinces like Hunan, Hubei and Jiangxi in autumn and winter, while in spring and summer, oceanic air masses from the East China Sea and South China Sea dominated. This divergence may be the main reason for the seasonal variation of PCDD/Fs concentrations in Guangzhou atmosphere.