秸秆燃烧排放的正构烷烃及其碳同位素组成特征

为了探讨生物质燃烧过程中正构烷烃化学组成及其碳同位素的变化规律,对4种玉米秸秆进行了室内焚烧实验,用GC-MS和GC/C/IRMS方法对燃烧前后的样品进行测定.结果表明,秸秆中正构烷烃的碳数为C13~C35,分布形态为单峰型,主峰碳数为C31.正构烷烃的碳优势指数(CPI)值为1.1~5.3,平均碳链长度(ACL)为25.1~28.8.明火烟尘中正构烷烃的碳数为C14~C35,呈双峰型分布,2个主峰碳数分别是C18和C31.其CPI值为1.0~2.4,ACL值为23.0~26.8.正构烷烃单体碳同位素比值为-20.1‰~-33.5‰.闷烧烟尘中正构烷烃的碳数是C12~C35,CPI值为2.2~4.8,ACL值为26.6~28.9.其含量呈双峰式分布,2个主峰碳数分别是C22/C23、C31.正构烷烃单体碳同位素比值为-21.5‰~-32.5‰.在明火烟尘和闷烧烟尘中,正构烷烃的单体碳同位素组成与原秸秆中同碳数正构烷烃的差值分别为-13.8‰~5.4‰、-6.7‰~ -5.1‰.2种烟尘中正构烷烃的化学组成与碳同位素分布都与原玉米秸秆有着显著的差别.

Chemical and stable carbon isotopic composition of n-alkanes in maize straw and its smoke

In order to investigate the relationships among the chemical and stable carbon isotopic compositions of n-alkanes in smoke from biomass combustion and in unburned biomass, four types of maize straw were burned in the laboratory under controlled condition, and GC-MS and GC/C/IRMS were used to analyze the samples. n-Alkanes in the straw were in the range of C13 to C35, and exhibited the distribution with only one peak at C31. The CPI and ACL values varied from 1.1to5.3 and from 25.1 to 28.8, respectively. The n-alkanes in the smoke generated in flaming condition were C14 to C35, and had a bimodal profile maximizing at C31 or C18. The CPI and ACL values ranged from 1.0 to 2.4 and from 23.0 to 26.8, respectively. The δ13C values of the individual n-alkanes varied from -20.1‰ to-33.5‰. The distribution of n-alkanes in the smoke released in smouldering condition was between C12 to C35, with a bimodal pattern maximizing at C31 (subordinant maximum at C22/C23). The values of CPI and ACL varied in the range of 2.2 to 4.8 and 26.6 to 28.9, respectively. The δ13C values of the individual n-alkanes ranged from -21.5‰to -32.5‰. The difference between the δ13C ratios for individual n-alkanes in the smoke and the straw ranged from -13.8‰ to 5.4‰ and -6.7‰ to 5.1‰, respectively. Apparently, great distinction exists among the chemical and carbon isotopic compositions of n-alkanes in the smoke and unburned maize straw.