Wavelength and NO x dependent complex refractive index of SOAs generated from the photooxidation of toluene
TL;DR: In this article, the complex refractive index (RI, m = n-ki values at 405, 532, and 781 nm of the secondary organic aerosols generated during the photooxidation of toluene (toluene-SOAs) under a variety of initial nitrogen oxide (NOx = NO + NO2) conditions were examined by photoacoustic spectroscopy (PAS) and cavity ring-down spectrography (CRDS).
Abstract: . Recently, secondary organic aerosols (SOAs) generated from anthropogenic volatile organic compounds have been proposed as a possible source of light-absorbing organic compounds, "brown carbon," in the urban atmosphere. However, the atmospheric importance of these SOAs remains unclear due to limited information about their optical properties. In this study, the complex refractive index (RI, m = n-ki values at 405, 532, and 781 nm of the SOAs generated during the photooxidation of toluene (toluene-SOAs) under a variety of initial nitrogen oxide (NOx = NO + NO2) conditions were examined by photoacoustic spectroscopy (PAS) and cavity ring-down spectroscopy (CRDS). The complex RI-values obtained in the present study and reported in the literature indicate that the k-value, which represents the light absorption of the toluene-SOAs, increased to shorter wavelengths at
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TL;DR: Understanding of the climate-related properties of atmospheric OC is still incomplete and the specific ways in which OC impacts atmospheric environment and climate forcing are just beginning to be understood.
Abstract: Organic carbon (OC) accounts for a large fraction of atmospheric aerosol and has profound effects on air quality, atmospheric chemistry and climate forcing. Molecular composition of the OC and its evolution during common processes of atmospheric aging have been a subject of extensive research over the last decade (see reviews of Ervens et al.,1 Hallquist et al.,2 Herckes et al.,3 Carlton et al.,4 Kroll and Seinfeld,5 Rudich et al.,6 and Kanakidou et al.7). Even though many fundamental advances have been reported in these studies, our understanding of the climate-related properties of atmospheric OC is still incomplete and the specific ways in which OC impacts atmospheric environment and climate forcing are just beginning to be understood. This review covers one topic of particular interest in this area –environmental chemistry of light-absorbing aerosol OC and its impact on radiative forcing.
1,026 citations
01 Dec 2007
TL;DR: In this article, the authors examined absorption spectra of primary organic carbon (OC) emitted from solid fuel pyrolysis and found that more than 92% was extractable by methanol or acetone compared with 73% for water and 52% for hexane.
Abstract: Abstract. Carbonaceous aerosols affect the radiative balance of the Earth by absorbing and scattering light. While black carbon (BC) is highly absorbing, some organic carbon (OC) also has significant absorption, especially at near-ultraviolet and blue wavelengths. To the extent that OC absorbs visible light, it may be a non-negligible contributor to positive direct aerosol radiative forcing. Quantification of that absorption is necessary so that radiative-transfer models can evaluate the net radiative effect of OC. In this work, we examine absorption by primary OC emitted from solid fuel pyrolysis. We provide absorption spectra of this material, which can be related to the imaginary refractive index. This material has polar character but is not fully water-soluble: more than 92% was extractable by methanol or acetone, compared with 73% for water and 52% for hexane. Water-soluble OC contributes to light absorption at both ultraviolet and visible wavelengths. However, a larger portion of the absorption comes from OC that is extractable only by methanol. Absorption spectra of water-soluble OC are similar to literature reports. We compare spectra for material generated with different wood type, wood size and pyrolysis temperature. Higher wood temperature is the main factor creating OC with higher absorption; changing wood temperature from a devolatilizing state of 210 °C to a near-flaming state of 360 °C causes about a factor of four increase in mass-normalized absorption at visible wavelengths. A clear-sky radiative transfer model suggests that, despite the absorption, both high-temperature and low-temperature OC result in negative top-of-atmosphere radiative forcing over a surface with an albedo of 0.19 and positive radiative forcing over bright surfaces. Unless absorption by real ambient aerosol is higher than that measured here, it probably affects global average clear-sky forcing very little, but could be important in energy balances over bright surfaces.
446 citations
302 citations
TL;DR: In this paper, the authors measured aerosol light absorption in the plumes with a half-life of 9 to 15 h, measured over day and night, during the 2013 NASA SEAC4RS mission.
Abstract: Particulate brown carbon (BrC) in the atmosphere absorbs light at subvisible wavelengths and has poorly constrained but potentially large climate forcing impacts. BrC from biomass burning has virtually unknown lifecycle and atmospheric stability. Here, BrC emitted from intense wildfires was measured in plumes transported over 2 days from two main fires, during the 2013 NASA SEAC4RS mission. Concurrent measurements of organic aerosol (OA) and black carbon (BC) mass concentration, BC coating thickness, absorption Angstrom exponent, and OA oxidation state reveal that the initial BrC emitted from the fires was largely unstable. Using back trajectories to estimate the transport time indicates that BrC aerosol light absorption decayed in the plumes with a half-life of 9 to 15 h, measured over day and night. Although most BrC was lost within a day, possibly through chemical loss and/or evaporation, the remaining persistent fraction likely determines the background BrC levels most relevant for climate forcing.
266 citations
Cites background from "Wavelength and NO x dependent compl..."
...…et al., 2013; Lack et al., 2013; Mohr et al., 2013] and secondary formation often involving carbonyl or aromatic compounds [Shapiro et al., 2009; Sareen et al., 2010; Kampf et al., 2012; Nguyen et al., 2012; Zarzana et al., 2012; Laskin et al., 2014; Nakayama et al., 2013; Yu et al., 2014]....
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..., 2013] and secondary formation often involving carbonyl or aromatic compounds [Shapiro et al., 2009; Sareen et al., 2010; Kampf et al., 2012; Nguyen et al., 2012; Zarzana et al., 2012; Laskin et al., 2014; Nakayama et al., 2013; Yu et al., 2014]....
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TL;DR: In this paper, size-resolved direct measurements of brown carbon were made at both urban (Atlanta), and rural (Yorkville) sites in Georgia, and brown carbon absorption was estimated based on Mie calculations using direct size-resolution measurements of chromophores in solvents.
Abstract: . Light absorbing organic carbon, often called brown carbon, has the potential to significantly contribute to the visible light-absorption budget, particularly at shorter wavelengths. Currently, the relative contributions of particulate brown carbon to light absorption, as well as the sources of brown carbon, are poorly understood. With this in mind size-resolved direct measurements of brown carbon were made at both urban (Atlanta), and rural (Yorkville) sites in Georgia. Measurements in Atlanta were made at both a representative urban site and a road-side site adjacent to a main highway. Fine particle absorption was measured with a multi-angle absorption photometer (MAAP) and seven-wavelength Aethalometer, and brown carbon absorption was estimated based on Mie calculations using direct size-resolved measurements of chromophores in solvents. Size-resolved samples were collected using a cascade impactor and analyzed for water-soluble organic carbon (WSOC), organic and elemental carbon (OC and EC), and solution light-absorption spectra of water and methanol extracts. Methanol extracts were more light-absorbing than water extracts for all size ranges and wavelengths. Absorption refractive indices of the organic extracts were calculated from solution measurements for a range of wavelengths and used with Mie theory to predict the light absorption by fine particles comprised of these components, under the assumption that brown carbon and other aerosol components were externally mixed. For all three sites, chromophores were predominately in the accumulation mode with an aerodynamic mean diameter of 0.5 μm, an optically effective size range resulting in predicted particle light absorption being a factor of 2 higher than bulk solution absorption. Mie-predicted brown carbon absorption at 350 nm contributed a significant fraction (20 to 40%) relative to total light absorption, with the highest contributions at the rural site where organic to elemental carbon ratios were highest. Brown carbon absorption, however, was highest by the roadside site due to vehicle emissions. The direct size-resolved measurement of brown carbon in solution definitively shows that it is present and optically important in the near-UV range in both a rural and urban environment during the summer when biomass burning emissions are low. These results allow estimates of brown carbon aerosol absorption from direct measurements of chromophores in aerosol extracts.
236 citations
Cites background from "Wavelength and NO x dependent compl..."
...Previous studies generally assume a small particle limit, where the particle size is not comparable to wavelength, when estimating particle light absorption from bulk solutions, in which case the factor is 0.69 to 0.75 (Nakayama et al., 2013; Sun et al., 2007)....
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References
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Book•
01 Jan 1983
TL;DR: In this paper, a Potpourri of Particles is used to describe surface modes in small Particles and the Angular Dependence of Scattering is shown to be a function of the size of the particles.
Abstract: BASIC THEORY. Electromagnetic Theory. Absorption and Scattering by an Arbitrary Particle. Absorption and Scattering by a Sphere. Particles Small Compared with the Wavelength. Rayleigh--Gans Theory. Geometrical Optics. A Potpourri of Particles. OPTICAL PROPERTIES OF BULK MATTER. Classical Theories of Optical Constants. Measured Optical Properties. OPTICAL PROPERTIES OF PARTICLES. Extinction. Surface Modes in Small Particles. Angular Dependence of Scattering. A Miscellany of Applications. Appendices. References. Index.
16,859 citations
01 Jan 2006
TL;DR: In this article, the authors present a model for the chemistry of the Troposphere of the atmosphere and describe the properties of the Atmospheric Aqueous phase of single aerosol particles.
Abstract: 1 The Atmosphere. 2 Atmospheric Trace Constituents. 3 Chemical Kinetics. 4 Atmospheric Radiation and Photochemistry. 5 Chemistry of the Stratosphere. 6 Chemistry of the Troposphere. 7 Chemistry of the Atmospheric Aqueous Phase. 8 Properties of the Atmospheric Aerosol. 9 Dynamics of Single Aerosol Particles. 10 Thermodynamics of Aerosols. 11 Nucleation. 12 Mass Transfer Aspects of Atmospheric Chemistry. 13 Dynamics of Aerosol Populations. 14 Organic Atmospheric Aerosols. 15 Interaction of Aerosols with Radiation. 16 Meteorology of the Local Scale. 17 Cloud Physics. 18 Atmospheric Diffusion. 19 Dry Deposition. 20 Wet Deposition. 21 General Circulation of the Atmosphere. 22 Global Cycles: Sulfur and Carbon. 23 Climate and Chemical Composition of the Atmosphere. 24 Aerosols and Climate. 25 Atmospheric Chemical Transport Models. 26 Statistical Models.
11,157 citations
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01 Jan 1997
TL;DR: In this paper, the authors present a model for the chemistry of the Troposphere of the atmosphere and describe the properties of the Atmospheric Aqueous phase of single aerosol particles.
Abstract: 1 The Atmosphere. 2 Atmospheric Trace Constituents. 3 Chemical Kinetics. 4 Atmospheric Radiation and Photochemistry. 5 Chemistry of the Stratosphere. 6 Chemistry of the Troposphere. 7 Chemistry of the Atmospheric Aqueous Phase. 8 Properties of the Atmospheric Aerosol. 9 Dynamics of Single Aerosol Particles. 10 Thermodynamics of Aerosols. 11 Nucleation. 12 Mass Transfer Aspects of Atmospheric Chemistry. 13 Dynamics of Aerosol Populations. 14 Organic Atmospheric Aerosols. 15 Interaction of Aerosols with Radiation. 16 Meteorology of the Local Scale. 17 Cloud Physics. 18 Atmospheric Diffusion. 19 Dry Deposition. 20 Wet Deposition. 21 General Circulation of the Atmosphere. 22 Global Cycles: Sulfur and Carbon. 23 Climate and Chemical Composition of the Atmosphere. 24 Aerosols and Climate. 25 Atmospheric Chemical Transport Models. 26 Statistical Models.
9,021 citations
"Wavelength and NO x dependent compl..." refers background in this paper
...Atmospheric aerosol plays an important role in determining the visibility, health effects, heterogeneous chemistry, and radiation balance of the atmosphere on a local and a global scale (Seinfeld and Pandis, 2006; Finlayson-Pitts and Pitts, 2000)....
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01 Mar 1984
4,579 citations
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...Qabs,sca,ext(Dp, λ) represent the absorption, scattering, and extinction efficiencies, and were calculated based on Mie theory using the BHMIE algorithm (Bohren and Huffman, 1983)....
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University of Gothenburg1, University College Cork2, Paul Scherrer Institute3, Weizmann Institute of Science4, Chalmers University of Technology5, Norwegian Meteorological Institute6, University of Antwerp7, Carnegie Mellon University8, University of Lyon9, Centre national de la recherche scientifique10, University of California, Berkeley11, University of York12, Leibniz Institute for Neurobiology13, University of Mainz14, University of Florida15, University of Colorado Boulder16, Forschungszentrum Jülich17, Ghent University18, University of Manchester19, Aix-Marseille University20, California Institute of Technology21
TL;DR: In this article, an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and analytical techniques used to determine the chemical composition of SOA is presented.
Abstract: Secondary organic aerosol (SOA) accounts for a significant fraction of ambient tropospheric aerosol and a detailed knowledge of the formation, properties and transformation of SOA is therefore required to evaluate its impact on atmospheric processes, climate and human health. The chemical and physical processes associated with SOA formation are complex and varied, and, despite considerable progress in recent years, a quantitative and predictive understanding of SOA formation does not exist and therefore represents a major research challenge in atmospheric science. This review begins with an update on the current state of knowledge on the global SOA budget and is followed by an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and the analytical techniques used to determine the chemical composition of SOA. A survey of recent laboratory, field and modeling studies is also presented. The following topical and emerging issues are highlighted and discussed in detail: molecular characterization of biogenic SOA constituents, condensed phase reactions and oligomerization, the interaction of atmospheric organic components with sulfuric acid, the chemical and photochemical processing of organics in the atmospheric aqueous phase, aerosol formation from real plant emissions, interaction of atmospheric organic components with water, thermodynamics and mixtures in atmospheric models. Finally, the major challenges ahead in laboratory, field and modeling studies of SOA are discussed and recommendations for future research directions are proposed.
3,324 citations