Russell Lynn M
Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08648, USA.
Environ Sci Technol. 2003 Jul 1;37(13):2982-7. doi: 10.1021/es026123w.
The ratio of organic-mass-to-organic-carbon, typically taken to be between 1.4 and 1.7, has an uncertainty higher than 50%, but this value is used in every measurement to date of the organic fraction of atmospheric particles. A recently developed technique with errors reduced to between 9% and 33% provides measurements of this ratio that show its large variability for samples measured in northeastern Asia and the Caribbean. The technique uses functional groups measured by FTIR spectroscopy to estimate composite organic carbon from the number of carbon bonds present and organic mass from the molecular mass of each functional group associated with the measured bond type. The molecular masses associated with each functional group are not unique and do not account for highly branched organic compositions. For the organic mixtures described by the less than 20% of atmospheric organic mass that has been speciated by GCMS, the theoretical discrepancy in the composite organic-mass-to-organic-carbon ratio is less than 5%. The measured ratios for submicron particle samples are skewed: over 90% of the measurements collected lie between 1.2 and 1.6, with mean values just below 1.4. This variability highlights the importance of measured organic-mass-to-organic-carbon ratios to reduce the uncertainty associated with atmospheric organic aerosol.
有机质量与有机碳的比率通常在1.4至1.7之间，其不确定性高于50%，但迄今为止，在大气颗粒物有机组分的每次测量中都使用了该值。最近开发的一种技术将误差降低到了9%至33%之间，该技术对这一比率的测量显示，在东北亚和加勒比地区测量的样本中，该比率存在很大的变异性。该技术利用傅里叶变换红外光谱法测量的官能团，根据存在的碳键数量估算复合有机碳，并根据与测量的键型相关的每个官能团的分子量估算有机质量。与每个官能团相关的分子量并非唯一，也未考虑高度支化的有机组成。对于气相色谱-质谱联用仪（GCMS）已鉴定出的占大气有机质量不到20%的有机混合物而言，复合有机质量与有机碳比率的理论差异小于5%。亚微米颗粒样本的测量比率存在偏差：超过90%的测量值在1.2至1.6之间，平均值略低于1.4。这种变异性凸显了测量有机质量与有机碳比率对于降低与大气有机气溶胶相关的不确定性的重要性。
