南京冬季雾天颗粒物中PAHs分布与气象条件的关系

Characteristics of polycyclic aromatic hydrocarbons(PAHs) in particles and the influence of foggy weather conditions during the winter in Nanjing

为研究南京冬季雾天PM10、PM2.5中PAHs的分布特征以及雾天气条件对其影响,2007年11月15日至12月30日分别于雾天和晴天采集了大气气溶胶PM10分级样品,测定了样品中的16种优控PAHs.结果表明,雾天PM10和PM2.5中Σ16PAHs质量浓度较晴天分别高出34.72,35.35ng/m^3,且昼夜变化没有晴天明显.低环PAHs在所在粒径段内占有比例逐渐递减,而高环PAHs逐渐增大.雾天苯并（a）芘（BaP）等效质量浓度（BaPE）超出BaP居民区标准（5.0ng/m^3）1.48ng/m^3.分析气象条件看出,雾天逆温层结稳定、相对湿度较大,且0.65-2.10μm粒子中PAHs质量浓度有增加的趋势,呈现出积聚模态颗粒物富集;雾天有东南暖湿气流和西南气流存在,为雾的发展提供了丰富水汽来源,带来的污染颗粒充当雾凝结核;同时弱风条件使上下层空气发生交换,雾体变厚,维持雾发展,加重了PAHs污染.

To study the distribution characteristics of polycyclic aromatic hydrocarbons（PAHs） in PM10 and PM2.5 and the influence of foggy weather conditions,aerosol samples were collected in foggy and sunny days in Nanjing,and the concentrations of 16 priority-controlled PAHs were analyzed by gas chromatography with mass selective detection（GC-MS）.The results suggest that the total concentrations of 16 PAHs in PM10 and PM2.5 during foggy days are higher by 34.72ng/m^3 and 35.35ng/m^3 respectively than those during sunny days.However,the diurnal variation in foggy days isn＇t exhibited,compared to sunny days.The proportion of low-ring PAHs in corresponding size ranges gradually decrease,while the high-ring PAHs gradually increase.Benzo（a） pyrene（BaP）-equivalent carcinogenic concentration（BaPE） in foggy days was higher by 1.48 ng/m^3 than the regional standard（BaP,5ng/m^3）.The analysis of meteorological conditions in foggy days shows that foggy days are characterized by the stable inversion layer and high relative humidity.Furthermore,the mass concentrations of 16 PAHs in particles in the range of 0.65μm to 2.10μm are gradually increases,exhibiting enrichment of accumulation mode.The existence of warm and moisture from southeast and southwest provides a rich source of water vapor and polluted particles which may act as fog condensation nuclei for fog,and at the same time,weak wind conditions are also proper for upper and lower air exchanging,resulting in a thicker fog,maintaining the development of fog,leading to significant increase of the PAHs pollution.