京津地区不同粒径大气颗粒物中的有机污染物

Organic Pollutants in Atmospheric Particulates of Various Sizes in Beijing and Tianjin

使用气溶胶粒度分布采样器对北京和天津不同地区的6个样点的大气颗粒物进行采样,结果得到的颗粒物质量浓度的归一化分布除个别点外均为双峰态。又采用加速溶剂提取仪萃取并分析了颗粒中的正构烷烃和多环芳烃,发现这些污染物在≤1.1～2.1μm和≥2.1～3.3μm的颗粒中具有明显不同的分布特征。正构烷烃在≤1.1～2.1μm的颗粒上开始具有双峰分布;2～3环PAHs随粒径的变化规律不明显,环数增加,PAHs含量随颗粒粒径减小而增加,在≤1.1～2.1μm颗粒上PAHs种类和含量增加明显。2～3环,4环,5～6环PAHs和PAH16(16种优控PAHs和)在≤1.1～2.1μm的颗粒上集中程度分别为45.3%～63.2%,62.7%～77.6%,86.4%～100%和65.9%～80.6%。颗粒物中不同环数PAHs及PAH16(16种优控PAHs总量)含量与粒径呈对数线性相关。本次采样结果显示,天津大气颗粒物中PAHs的污染比北京严重,北京城区颗粒物中PAHs的含量高于郊区。

The size distributions of atmospheric particulates sampled using a FA- 3 aerosol cascade sampler from 2 locations in Beijing and 4 locations in Tianjin was measured during heating season 2002— 2003. The particulate matters were separated into the following size ranges according to particle aerodynamic diameter dae: <0.43 (backup filter), 0.43～ 0.65, 0.65～ 1.1, 1.1～ 2.1, 2.1～ 3.3, 3.3～ 4.7, 4.7～ 5.8, 5.8～ 9.0 and >9.0(m when the flow rate was calculated at 28.3 L· min- 1. Bimodal distribution of size was obtained with the first peak in the fine mode (1.1～ 2.1 μ m) and the second peak in the coarse mode (5.8～ 9.0 μ m). The concentration ratios of coarse mode (dae≥ 2.1～ 3.3 μ m) to fine mode (dae≤ 1.1～ 2.1 μ m) were 1.42 and 0.89 for Beijing and Tianjin samples,respectively.The average atmospheric concentrations of complete size particles were 0.261mg· m- 3 (Beijing) and 0.146mg· m- 3(Tianjin). The airborne particles from the 6 sites were analyzed for aliphatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) using GC/MS. The normalized distribution of n- Alkane (C12～ C33) was bimodal within the range of ≤ 1.1～ 2.1 μ m and unimodal in the range of ≥ 2.1～ 3.3 μ m. The CPI (Carbon Preference Index) values ranged from 0.88 to 1.19, clearly reflecting the major source of anthropogenic activities. The n- Alkane >C27 showed slight odd homolog predominance due to an origin from natural plant wax. 62.55% ～ 77.61% of the four rings PAHs and 86.43% ～ 100% of the PAHs with five or more rings were associated with the particles with aerodynamic diameter of ≤ 1.1～ 2.1 μ m. The concentrations of high molecular weight PAHs with four to six rings increased steadily with decreasing particle size, while this trend didn't occur in the small molecular weight PAHs with two and three ring. Linear correlations were found between the ring numbers of PAHs, the content of PAH16 in the particles and the log- transformed particle size. The levels of PAHs in atmospheric particulates from Tianjin were higher than those from Beijing, and those from urban were higher than from suburb in Beijing.