西安冬季PM_(10)中正构烷烃昼夜变化特征

Diurnal variation of n-Alkanes in atmospheric PM_(10) during winter in Xi'an

利用中流量颗粒物采样器于2009年1月14—21日和2月7—12日分昼夜采集了西安市大气中PM_(10)样品,应用气相色谱-质谱联用仪分析了PM_(10)中正构烷烃C_(18)~C_(36)(19种)。结果表明,西安市冬季正常天气下PM_(10)昼夜浓度分别为(432±143)μg·m^(-3)、(444±139)μg·m^(-3),无显著的昼夜差异,但是元宵节期间PM_(10)夜间浓度(595μg·m^(-3))高于白天(385μg·m^(-3))。冬季正常天气下PM_(10)中总正构烷烃(∑n-alkanes)白天(836±668 ng·m^(-3))低于夜间(1100±695 ng·m^(-3)),而元宵节期间∑n-alkanes白天浓度(708 ng·m^(-3))却高于夜间(577 ng·m^(-3))。两个采样时段昼夜正构烷烃主峰碳变化趋势一致,为双峰型分布,低碳数(C<25)主峰碳为C_(23),高碳数(C>25)主峰碳为C^(29),且具有明显的奇数碳优势。昼夜正构烷烃的CPI指数结果显示,西安市冬季大气可吸入颗粒物中正构烷烃主要由化石燃料的不完全燃烧产生,PM_(10)中来自生物源和矿物燃料源的正构烷烃分别为13%~36%、64%~87%。

PM10 samples were collected in Xi＇an between 14--21 Jan. and 7--12 Feb. 2009 with middle volume sampler, and n-alkanes in the samples were measured for molecular compositions and concentrations using a gas chromatography-mass spectrometry （GC-MS）technique. The results showed that PM10 were 444 ± 139 and 432 ± 143μg·m^-3 in the day and night with no significant diurnal difference. The n-alkanes homologue （C18 -C36 ） were characterized by a bimodal molecular distribution during the two sampling periods, peaking at C23 and C29 respectively. The total n-alkanes in normal days were higher in the nighttime （1100±695 ng ·m^-3） than in the daytime （836±668 ng ·m^-3）, in contrast to the diurnal variation on the Lantern Festival day, which was higher in the daytime （708 ng ·m^-3） than in the nighttime （577 ng ·m^-3）. CPI and WNA% of the n-alkanes indicated that the compounds mainly originated from incomplete combustion of fossil fuels, accounting for 64% ~ 87% of the total with the remaining （ 13% - 36% ） derived from biogenic sources.