麦秸及其烟尘中正构脂肪酸的组成

在不同燃烧条件下对6种麦草进行焚烧,并利用GC/MS对麦秸和烟尘中的正构脂肪酸进行了测定.结果表明,烟尘中含有碳数C8~C32的正构脂肪酸.在明火烟尘中,正构脂肪酸总含量分布于1 509.3~10 543.7 mg·kg-1之间,平均值为5 871.2mg·kg-1.其轻(C8~C16)、重(C17~C32)正构脂肪酸含量之比(L/H)为0.8~5.3,平均值为2.8;C14/C16、C28/C16、C30/C16等比值的平均值分别为16.5%、14.1%、11.4%.正构脂肪酸呈双峰式分布,其主峰碳数是C16,次峰碳数是C28或C30,且具有显著的偶碳数优势.其碳优势指数(CPI)和平均碳链长度(ACL)的平均值分别为19.8和18.2.在闷烧烟尘中,正构脂肪酸的总含量为5 799.3~37 244 mg·kg-1,平均值为15 838.6 mg·kg-1.其L/H值介于1.2~5.6之间,平均为4.2;C14/C16、C28/C16、C30/C16的平均值分别为12.7%、10.1%、6.0%.闷烧烟尘中正构脂肪酸的分布模式与明火烟尘的类似,其CPI和ACL的平均值分别为24.7和17.7.总之,虽然两类烟尘和麦秸中的正构脂肪酸均具有类似的分布模式和偶碳数优势,但三者在组成上仍然存在明显的差别.这有助于识别大气气溶胶中麦秸及其燃烧排放的正构脂肪酸.

Chemical Compositions of n-Alkanoic Acids in Wheat Straw and Its Smoke

Wheat straws of six genotypes were burned under different conditions, and n-alkanoic acids in the straw and its smoke were measured by GC/MS. The results showed that the carbon number of the fatty acids in all the smoke ranged from C₈ to C₃₂. In the flaming smoke, the total amounts of the compounds varied from 1509.3 to 10543.7 mg·kg^-1, with a mean value of 5871.2 mg·kg^-1. And the content ratio values of n-alkanoic acids with low carbon number (C₈ to C₁₆) to those with high carbon number (C₁₇ to C₃₂) (L/H) were between 0.8 and 5.3, with an average of 2.8. In addition, the mean values for C₁₄/C₁₆, C₂₈/C₁₆ and C₃₀/C₁₆ were 16.5%,14.1% and 11.4%, respectively. The distribution of the compounds in the smoke was bimodal with the peak carbon number of C₁₆ followed by C₂₈ or C₃₀, and it showed an even carbon number preference. The mean values of carbon preference index (CPI) and average carbon chain length (ACL) were 19.8 and 18.2, respectively. In the smoldering smoke,the total amounts of the fatty acids were in the range of 5799.3 to 37244 mg·kg^-1, and the mean was 15838.6 mg·kg^-1. Moreover, the L/H ratios varied from 1.2 to 5.6, with a mean value of 4.2.The average ratio values for C₁₄/C₁₆, C₂₈/C₁₆ and C₃₀/C₁₆ were 12.7%, 10.1% and 6.0%, respectively. The content distribution pattern of the compounds was similar to that in the flaming smoke, and the mean values of CPI and ACL were 24.7 and 17.7, respectively. In general, n-alkanoic acids in both wheat straw and its two types of smoke had similar distribution modes, both with even carbon number preference, but there was prominent distinction among the chemical compositions of the compounds in the straw and the smokes. This is maybe useful in identifying the organic matter from wheat straw or its smoke in the atmospheric aerosol.