Derivation of the Density and Refractive Index of Organic Matter and Elemental Carbon from Closure between Physical and Chemical Aerosol Properties

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• 作者：Otmar Schmid* ; Duli Chand^‡ ; ; Erwin Karg^† ; ; Pascal Guyon^‡ ; ; Gran P. Frank^‡ ; ^§ ; ; Erik Swietlicki^§ ;
• 刊名：Environmental Science & Technology
• 出版年：2009
• 出版时间：February 15, 2009
• 年：2009
• 卷：43
• 期：4
• 页码：1166-1172
• 全文大小：177K
• 年卷期：v.43,no.4(February 15, 2009)
• ISSN：1520-5851

文摘

Information on the density (ρ) and refractive index m (=n − ik) of elemental carbon (EC_a) and organic matter (OM_a), the main carbon components of atmospheric aerosols, has frequently been obtained from closure calculations between physical and chemical aerosol properties. However, this approach has suffered from large uncertainties since there were more unknown (or poorly known) parameters than defining equations. In this study, we propose a method that avoids this ambiguity mainly by considering both optical and mass closure and by expressing the three EC_a parameters (ρ_ECa, n_ECa, k_ECa) by a single (unknown) parameter. This allows mathematically rigorous determination of ρ_ECa, m_ECa, ρ_OMa and m_OMa from standard physico-chemical aerosol data and rigorous error analysis. The results are unambiguous and self-consistent, i.e., there is no difference between the chemically and physically derived ρ and m values of the atmospheric aerosol. Application of this method to our previously published data on biomass burning particles from Amazonia yields ρ_ECa = 1.8(±0.2) g/cm³, m_ECa = 1.9(±0.1)-i0.20(−0.04/+0.02), ρ_OMa = 1.39(±0.13) g/cm³ and m_OMa = 1.46(±0.02), where the 1σ uncertainty limits given in parenthesis are based on the principles of error propagation. The relatively low imaginary part of m_ECa indicates the presence of only partially graphitized elemental carbon, which is consistent with biomass burning aerosol dominated by smoldering combustion conditions.