Department of Chemistry, Memorial University , St. John's, Newfoundland A1B 3X5, Canada.
Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder , Boulder, Colorado 80309, United States.
Environ Sci Technol. 2017 Mar 21;51(6):3128-3137. doi: 10.1021/acs.est.6b06160. Epub 2017 Mar 1.
Biomass burning is a known source of brown carbon aerosol in the atmosphere. We collected filter samples of biomass-burning emissions at three locations in Canada and the United States with transport times of 10 h to >3 days. We analyzed the samples with size-exclusion chromatography coupled to molecular absorbance spectroscopy to determine absorbance as a function of molecular size. The majority of absorption was due to molecules >500 Da, and these contributed an increasing fraction of absorption as the biomass-burning aerosol aged. This suggests that the smallest molecular weight fraction is more susceptible to processes that lead to reduced light absorption, while larger-molecular-weight species may represent recalcitrant brown carbon. We calculate that these large-molecular-weight species are composed of more than 20 carbons with as few as two oxygens and would be classified as extremely low volatility organic compounds (ELVOCs).
生物质燃烧是大气中棕色碳气溶胶的已知来源。我们在加拿大和美国的三个地点采集了生物质燃烧排放物的滤膜样本，其输送时间为 10 小时至超过 3 天。我们使用尺寸排阻色谱法结合分子吸收光谱法对样品进行分析，以确定吸光度随分子大小的变化。大部分吸收是由于分子量大于 500 Da 的分子引起的，随着生物质燃烧气溶胶的老化，这些分子对吸收的贡献越来越大。这表明，分子量最小的部分更容易受到导致光吸收减少的过程的影响，而较大分子量的物质可能代表难降解的棕色碳。我们计算得出，这些大分子量物质由 20 个以上的碳原子组成，氧原子数少至两个，将被归类为极难挥发有机化合物（ELVOCs）。
