Emmenegger Christian, Reinhardt Alain, Hueglin Christoph, Zenobi Renato, Kalberer Markus
Department of Chemistry and Applied Biosciences, Wolfgang-Paulistrasse 10, ETH Zürich, CH-8093 Zürich, Switzerland.
Environ Sci Technol. 2007 Apr 1;41(7):2473-8. doi: 10.1021/es061095t.
The chemical composition of organic atmospheric aerosols is only poorly understood. Although a significant fraction of organic aerosols consists of humic-like substances (HULIS), only little is known about this class of compound, and accurate quantification remains difficult, partly due to the lack of appropriate standards. Here, evaporative light-scattering detection (ELSD) was applied for the first time to quantify water-soluble HULIS in aerosol particles smaller than 1 microm. This detection method was shown to be suitable for the quantification of compounds with unknown structures and lacking appropriate quantification standards. As compared to organic carbon determination of isolated HULIS, no organic carbon/organic mass (OC/OM) conversion factor needs to be applied with ELSD and therefore eliminates this significant uncertainty factor of the OC/OM method, which is frequently used to quantify HULIS. Solid-phase extraction and size-exclusion chromatography were applied to separate inorganic ions and low molecular weight compounds from HULIS before ELSD quantification. The ELSD itself provides an additional separation step where low volatility HULIS are separated from high volatility, small compounds. Electrospray ionization mass spectrometry was used to identify the molecular weight range of the compounds quantified with ELSD. The most intensive peaks were in the range of m/z 200-500, with some masses upto m/z800. We showed that UV detection using fulvic acid as surrogate quantification standard underestimates the HULIS concentration by a factor of 1.1 to 2.5, which is in agreement with earlier studies. During a 6 week winter 2005-2006 campaign at a suburban site near Zurich, Switzerland, an average of 1.1 microg/m(3) HULIS was found, which is about4-6% of the total particle mass smaller than 1 microm (PM1) and 10-35% of the organic matter in PM1.
有机大气气溶胶的化学成分目前了解甚少。尽管相当一部分有机气溶胶由类腐殖质（HULIS）组成，但对于这类化合物我们知之甚少，而且由于缺乏合适的标准品，准确量化仍然困难重重。在此，首次应用蒸发光散射检测（ELSD）对直径小于1微米的气溶胶颗粒中的水溶性HULIS进行定量分析。结果表明，这种检测方法适用于对结构未知且缺乏合适定量标准品的化合物进行定量分析。与分离出的HULIS的有机碳测定相比，ELSD无需应用有机碳/有机质量（OC/OM）转换因子，因此消除了常用于量化HULIS的OC/OM方法中这个显著的不确定因素。在ELSD定量分析之前，采用固相萃取和尺寸排阻色谱法将无机离子和低分子量化合物与HULIS分离。ELSD本身提供了一个额外的分离步骤，可将低挥发性的HULIS与高挥发性的小分子化合物分离。采用电喷雾电离质谱法确定用ELSD定量分析的化合物的分子量范围。最强的峰出现在m/z 200 - 500范围内，有些质量数高达m/z 800。我们发现，以富里酸作为替代定量标准品的紫外检测法会使HULIS浓度低估1.1至2.5倍，这与早期研究结果一致。在2005 - 2006年冬季为期6周的时间里，于瑞士苏黎世附近的一个郊区站点进行监测，结果发现HULIS的平均浓度为1.1微克/立方米，约占直径小于1微米的总颗粒物质量（PM1）的4 - 6%，以及PM1中有机物的10 - 35%。
