[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 1,509.3 to 10,543.7 mg x kg(- ), with a mean value of 5,871.2 mg x 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 5,799.3 to 37,244 mg x kg(-1), and the mean was 15,838.6 mg x 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.