Spectroscopic comparison of water- and methanol-soluble brown carbon particulate matter
Spectroscopic comparison of water- and methanol-soluble brown carbon particulate matter
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DOI：
10.1080/02786826.2017.1334109
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发表时间：
2017-01-01
影响因子：
5.2
通讯作者：
Smith, Geoffrey D.
中科院分区：
文献类型：
--
作者：
Phillips, Sabrina M.;Smith, Geoffrey D.
现在人们认识到，环境气溶胶的一些有机成分吸收的光谱与黑碳和矿物成分等其他吸收剂吸收的光谱不同。分离这种吸收光的有机组分或“棕色碳”的最常用方法是在过滤器上收集颗粒物，然后在溶剂中提取，通常是水或甲醇。在这里，我们比较了从乔治亚州雅典的环境样品中提取的水溶性（WS）和甲醇可溶性（MS）提取物的吸收光谱。我们发现，尽管注射器过滤的MS提取物，消光由悬浮粒子是明显的光谱导致吸收高估平均两倍的因素。在WS提取物中没有明显的颗粒消失。我们证明，可以通过将光谱拟合为两个幂律函数的和来减去MS提取物中的消光贡献，其中一个幂律函数描述吸收光谱，另一个描述消光光谱。消除消光后，我们发现MS棕碳萃取物的综合吸收（300-800 nm）与WS萃取物高度相关，平均高出1.55倍。WS和MS光谱的波长依赖性也与平均吸收埃氏指数分别为6.1（+/- 0.7）和6.7（+/- 1.1）相关且非常相似。本研究表明，对于所收集的样品：(1)如果不考虑MS光谱中的散射，棕碳吸收可能会被高估；(2)没有光谱证据表明WS和MS的发色团不同；(3)使用一个简单的比例因子可以使用WS光谱来表示棕碳的总吸收。这些发现可能与其他类型的气溶胶样品和分析方法不同。
It is now recognized that some organic components of ambient aerosols absorb light with a spectrum distinct from that of other absorbers such as black carbon and mineral components. The most common method for isolating this light-absorbing organic fraction, or "brown carbon," is to collect particulate matter on filters and extract in a solvent, usually water or methanol. Here, we compare the absorption spectra of water-soluble (WS) and methanol-soluble (MS) extracts from ambient samples collected in Athens, Georgia. We find that despite syringe filtering the MS extracts, extinction by suspended particles is evident in the spectra leading to an overestimation of absorption by a factor of two on average. No such particle extinction is evident in the WS extracts. We demonstrate that it is possible to subtract the extinction contribution in the MS extracts by fitting the spectrum to the sum of two power-law functions, one describing the absorption spectrum and the other describing the extinction spectrum. With extinction thus removed, we find that integrated absorption (300-800 nm) by the MS brown carbon extract is highly correlated with the WS extract and is on average 1.55x larger. The wavelength dependence of the WS and MS spectra are also correlated and very similar with average absorption Angstrom exponents of 6.1 (+/- 0.7) and 6.7 (+/- 1.1), respectively. This study demonstrates that for the samples collected: (1) brown carbon absorption can be overestimated if scattering in MS spectra is not accounted for, (2) there is no spectral evidence that the WS and MS chromophores are different, and (3) it may be possible to use WS spectra to represent total brown carbon absorption using a simple scaling factor. These findings may differ for other types of aerosol samples and analytical methods.