厦门冬春季大气VOCs的污染特征及臭氧生成潜势

2014年1~4月在厦门市城区和郊区开展冬春季节大气样品的采集,采用大气预浓缩系统与GC/MS联用技术定量了48种大气挥发性有机物(VOCs),对比分析了冬春季城区和郊区大气VOCs的污染特征,并利用最大增量反应活性(MIR)估算了大气VOCs的臭氧生成潜势(OFP).结果表明,冬季厦门城区和郊区大气中VOCs的平均体积分数分别为11.13×10-9和7.17×10-9,春季厦门城区和郊区大气中VOCs的平均体积分数分别为24.88×10-9和11.27×10-9,且均表现为烷烃芳香烃烯烃.通过B/T值探讨城区和郊区VOCs的来源发现,机动车和溶剂挥发是城区VOCs的主要来源,郊区VOCs除了局地源的贡献外,还受到外来污染物扩散传输的影响.城、郊区的主要VOCs包括丙烯、正丁烷、异丁烷、正戊烷、异戊烷、正己烷、苯、甲苯、乙苯和间对二甲苯,这10种组分对两地VOCs的贡献表现为春季(城区和郊区分别为62.83%和53.74%)高于冬季(城区和郊区分别为61.57%和45.83%).城、郊区VOCs的臭氧生成潜势分析显示,芳香烃的相对贡献率最大,其次是烯烃,烷烃最小.C3、C4类烯烃和苯系物是厦门城区和郊区活性较高的物种,对臭氧的贡献较大.比较观测期间城区和郊区VOCs的平均MIR值可知,郊区VOCs的活性高于城区.

Pollution Characteristics and Ozone Formation Potential of Ambient VOCs in Winter and Spring in Xiamen

Air samples were collected at urban and rural sites in Xiamen from January to April 2014. The concentrations of 48 ambient volatile organic compounds(VOC) species were measured by the method of cryogenic pre-concentrator and gas chromatography-mass spectrometry(GC/MS). The ozone formation potential(OFP) of VOCs was also calculated with the method of maximum incremental reactivity(MIR). The results showed that the average mixing ratios of VOCs in winter were 11.13×10^-9 and 7.17×10^-9 at urban and rural sites, respectively, and those in spring were 24.88×10^-9 and 11.27×10^-9 at urban and rural sites, respectively. At both sites, alkanes contributed the most to VOCs, followed by aromatics and alkenes. The ratios of B/T showed that vehicle and solvent evaporation were the main sources of VOCs at urban site. While at rural site, transport of anthropogenic sources was another important source of VOCs besides local biomass emissions. Ten main components including propene, n-butane, i-butane, n-pentane, i-pentane, n-hexane, benzene, toluene, ethylbenzene and m/p-xylene accounted for 61.57% and 45.83% of total VOCs at urban and rural sites in winter, respectively, and 62.83% and 53.74% at urban and rural sites in spring, respectively. Aromatics contributed the most to total OFP, followed by alkenes. Alkanes contributed the least to OFP with the highest concentration. C₃, C₄ alkenes and aromatics were found to be the more reactive species with relatively high contributions to ozone formation in Xiamen. Comparing the average MIR of VOCs at the two sites, it was found that the reactivity of VOCs at rural site was higher than that at urban site.