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

Abstract

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 1.1 to 5.3 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.