北京西三环地区不同粒径大气颗粒物中有机脂肪酸的污染特性

年1—7月在北京市西三环航天桥地区,用大流量分级采样器分5级采集大气颗粒物样品,采用溶剂提取和衍生化方法对样品进行前处理,利用GC-MS分析不同粒径颗粒物中的有机脂肪酸. 结果表明:在颗粒物中共检出21种MOA(一元有机脂肪酸)和7种DIA(二元有机脂肪酸)；ρ(∑₂₁MOA)(21种MOA总质量浓度)和ρ(∑₇DIA)(7种DIA总质量浓度)均在粒径<0.69μm的超细颗粒中最高,分别约占各自5级颗粒物质量浓度总和的30.0%和32.5%；颗粒物中ρ(∑₂₁MOA)和ρ(∑₇DIA)月际变化规律不同,前者在1—2月最高,3月次之；而后者在5—7月最高. MOA和DIA的组成、分布特点亦不尽相同,其中C₁₀~C₂₄的MOA表现出明显的偶数碳优势,而DIA没有显现奇偶优势；MOA中ρ(C₁₆-MOA)最高,ρ(C₁₈-MOA)次之；DIA中ρ(壬二酸)最高. 基于MOA的C₁₈/C₁₆〔ρ(C₁₈-MOA)/ρ(C₁₆-MOA)〕和CPI(碳优先指数)分析表明,颗粒物中MOA主要来自人为源,与燃煤排放、机动车尾气及烹调排放相关,1—2月燃煤排放对颗粒物中MOA的贡献明显. 

Distribution Characteristics of Organic Aliphatic Acids in Airborne Particles with Different Sizes in the Area of the 3rd West Ring Road in Beijing City

Particulate samples were collected by the multi-stage impactor sampler and classified into five grades by their sizes from January to July in 2012in the area of the 3rd west ring road in Beijing City. The organic aliphatic acids in the samples were determined by GC-MS after the pretreatment of solvent extraction and derivation. Twenty one monocarboxylic aliphatic acids and seven dicarboxylic aliphatic acids were separately determined. The results showed that both acids had a tendency to concentrate in ultrafine particles which were smaller than 0.69μm. For the two acids, ρ<0.69(∑₂₁MOA) and ρ<0.69(∑₇DIA) accounted for 30.0% and 32.5% of the concentration of all stages particles, respectively. The monthly variations with concentrations of monocarboxylic aliphatic acids and dicarboxylic aliphatic acids appeared quite different. ρ(∑₂₁MOA) were much higher obviously for January and February and were the second in March. However, the highest values of ρ(∑₇DIA) appeared from May to July. There were obvious differences in composition characteristics of the two acids. The monocarboxylic aliphatic acids in the ranges C₁₀~C₂₄ had a significant even number predominances, while dicarboxylic aliphatic acids presented no parity preponderance. For the fatty acids, the concentration of hexadecanoic acid was the highest followed by octadecanoic acid; Nonandioic acid presented the highest concentration in dicarboxylic acids. Preliminary analysis based on the ratios of C₁₈/C₁₆ and the CPI showed that monocarboxylic aliphatic acids mainly caused by human activities such as coal combustion, vehicle exhaust and cooking emission. For instance, the most important source of fatty acids was coal burning in January and February.