scholarly journals Black carbon or brown carbon? The nature of light-absorbing carbonaceous aerosols

2006 ◽  
Vol 6 (3) ◽  
pp. 3419-3463 ◽  
Author(s):  
M. O. Andreae ◽  
A. Gelencsér
Keyword(s):  
Black Carbon ◽  
Measurement Methods ◽  
Carbonaceous Aerosols ◽  
Carbonaceous Matter ◽  
Scientific Controversy ◽  
Laboratory Studies ◽  
Brown Carbon ◽  
Aerosol Absorption ◽  
Wavelength Light ◽  
Absorption Measurements

Abstract. Although the definition and measurement methods of atmospheric ''black carbon'' (''BC'') have long been subjects of scientific controversy, the recent discovery of light-absorbing carbon that is not black (''brown carbon, Cbrown'') makes it imperative to reassess and redefine the components that make up light-absorbing carbonaceous matter (LAC) in the atmosphere. Evidence for the atmospheric presence of Cbrown comes directly from aerosol absorption measurements near specific combustion sources, from observations of spectral properties of water extracts of continental aerosol, from laboratory studies indicating the formation of light-absorbing organic matter in the atmosphere, and indirectly from the chemical analogy of aerosol species to colored natural humic substances. We show that these species may severely bias measurements of ''BC'' and ''EC'' over vast parts of the troposphere, where mass concentration of Cbrown is high relative to that of combustion soot. We also imply that due to the strongly skewed absorption of Cbrown towards the UV, single-wavelength light absorption measurements may not be adequate for the assessment of absorption of solar radiation in the troposphere. The possible consequences of these effects on our understanding of tropospheric processes are discussed.

scholarly journals Black carbon or brown carbon? The nature of light-absorbing carbonaceous aerosols

2006 ◽  
Vol 6 (10) ◽  
pp. 3131-3148 ◽  
Author(s):  
M. O. Andreae ◽  
A. Gelencsér
Keyword(s):  
Black Carbon ◽  
Light Absorption ◽  
Spectral Properties ◽  
Measurement Techniques ◽  
Optical Measurements ◽  
Carbonaceous Aerosols ◽  
Scientific Controversy ◽  
Brown Carbon ◽  
Chemical Complexity ◽  
Absorption Measurements

Abstract. Although the definition and measurement techniques for atmospheric "black carbon" ("BC") or "elemental carbon'' ("EC") have long been subjects of scientific controversy, the recent discovery of light-absorbing carbon that is not black ("brown carbon, Cbrown") makes it imperative to reassess and redefine the components that make up light-absorbing carbonaceous matter (LAC) in the atmosphere. Evidence for the atmospheric presence of Cbrown comes from (1) spectral aerosol light absorption measurements near specific combustion sources, (2) observations of spectral properties of water extracts of continental aerosol, (3) laboratory studies indicating the formation of light-absorbing organic matter in the atmosphere, and (4) indirectly from the chemical analogy of aerosol species to colored natural humic substances. We show that brown carbon may severely bias measurements of "BC" and "EC" over vast parts of the troposphere, especially those strongly polluted by biomass burning, where the mass concentration of Cbrown is high relative to that of soot carbon. Chemical measurements to determine "EC" are biased by the refractory nature of Cbrown as well as by complex matrix interferences. Optical measurements of "BC" suffer from a number of problems: (1) many of the presently used instruments introduce a substantial bias into the determination of aerosol light absorption, (2) there is no unique conversion factor between light absorption and "EC" or "BC" concentration in ambient aerosols, and (3) the difference in spectral properties between the different types of LAC, as well as the chemical complexity of Cbrown, lead to several conceptual as well as practical complications. We also suggest that due to the sharply increasing absorption of Cbrown towards the UV, single-wavelength light absorption measurements may not be adequate for the assessment of absorption of solar radiation in the troposphere. We discuss the possible consequences of these effects for our understanding of tropospheric processes, including their influence on UV-irradiance, atmospheric photochemistry and radiative transfer in clouds.

scholarly journals Production of particulate brown carbon during atmospheric aging of residential wood-burning emissions

2018 ◽  
Vol 18 (24) ◽  
pp. 17843-17861 ◽  
Author(s):  
Nivedita K. Kumar ◽  
Joel C. Corbin ◽  
Emily A. Bruns ◽  
Dario Massabó ◽  
Jay G. Slowik ◽  
...  
Keyword(s):  
Black Carbon ◽  
Light Absorption ◽  
Wavelength Dependence ◽  
Organic Aerosol ◽  
Geometric Standard Deviation ◽  
Wood Combustion ◽  
Brown Carbon ◽  
Atmospheric Aging ◽  
Aerosol Absorption ◽  
Uv Visible

Abstract. We investigate the optical properties of light-absorbing organic carbon (brown carbon) from domestic wood combustion as a function of simulated atmospheric aging. At shorter wavelengths (370–470 nm), light absorption by brown carbon from primary organic aerosol (POA) and secondary organic aerosol (SOA) formed during aging was around 10 % and 20 %, respectively, of the total aerosol absorption (brown carbon plus black carbon). The mass absorption cross section (MAC) determined for black carbon (BC, 13.7 m2 g−1 at 370 nm, with geometric standard deviation GSD =1.1) was consistent with that recommended by Bond et al. (2006). The corresponding MAC of POA (5.5 m2 g−1; GSD =1.2) was higher than that of SOA (2.4 m2 g−1; GSD =1.3) at 370 nm. However, SOA presents a substantial mass fraction, with a measured average SOA ∕ POA mass ratio after aging of ∼5 and therefore contributes significantly to the overall light absorption, highlighting the importance of wood-combustion SOA as a source of atmospheric brown carbon. The wavelength dependence of POA and SOA light absorption between 370 and 660 nm is well described with absorption Ångström exponents of 4.6 and 5.6, respectively. UV-visible absorbance measurements of water and methanol-extracted OA were also performed, showing that the majority of the light-absorbing OA is water insoluble even after aging.

scholarly journals Direct radiative effect by brown carbon over the Indo-Gangetic Plain

2015 ◽  
Vol 15 (22) ◽  
pp. 12731-12740 ◽  
Author(s):  
A. Arola ◽  
G. L. Schuster ◽  
M. R. A. Pitkänen ◽  
O. Dubovik ◽  
H. Kokkola ◽  
...  
Keyword(s):  
Winter Season ◽  
Carbonaceous Aerosols ◽  
Radiative Effect ◽  
Gangetic Plain ◽  
Brown Carbon ◽  
Relative Significance ◽  
Aerosol Absorption ◽  
Spectrally Resolved ◽  
First Time ◽  
Indo Gangetic Plain

Abstract. The importance of light-absorbing organic aerosols, often called brown carbon (BrC), has become evident in recent years. However, there have been relatively few measurement-based estimates for the direct radiative effect of BrC so far. In earlier studies, the AErosol RObotic NETwork (AERONET)-measured aerosol absorption optical depth (AAOD) and absorption Angstrom exponent (AAE) were exploited. However, these two pieces of information are clearly not sufficient to separate properly carbonaceous aerosols from dust, while imaginary indices of refraction would contain more and better justified information for this purpose. This is first time that the direct radiative effect (DRE) of BrC is estimated by exploiting the AERONET-retrieved imaginary indices. We estimated it for four sites in the Indo-Gangetic Plain (IGP), Karachi, Lahore, Kanpur and Gandhi College. We found a distinct seasonality, which was generally similar among all the sites, but with slightly different strengths. The monthly warming effect up to 0.5 W m−2 takes place during the spring season. On the other hand, BrC results in an overall cooling effect in the winter season, which can reach levels close to −1 W m−2. We then estimated similarly also the DRE of black carbon and total aerosol, in order to assess the relative significance of the BrC radiative effect in the radiative effects of other components. Even though BrC impact seems minor in this context, we demonstrated that it is not insignificant. Moreover, we demonstrated that it is crucial to perform spectrally resolved radiative transfer calculations to obtain good estimates for the DRE of BrC.

scholarly journals Aerosol light absorption and the role of extremely low volatility organic compounds

2020 ◽  
Vol 20 (19) ◽  
pp. 11625-11637
Author(s):  
Antonios Tasoglou ◽  
Evangelos Louvaris ◽  
Kalliopi Florou ◽  
Aikaterini Liangou ◽  
Eleni Karnezi ◽  
...  
Keyword(s):  
Black Carbon ◽  
Organic Compounds ◽  
Light Absorption ◽  
Absorption Enhancement ◽  
Scanning Mobility Particle Sizer ◽  
Brown Carbon ◽  
Aerosol Absorption ◽  
Aerosol Mass ◽  
Particle Sizer

Abstract. A month-long set of summertime measurements in a remote area in the Mediterranean is used to quantify aerosol absorption and the role of black and brown carbon. The suite of instruments included a high-resolution aerosol mass spectrometer (HR-ToF-AMS) and a scanning mobility particle sizer (SMPS), both coupled to a thermodenuder and an Aethalometer, a photoacoustic extinctiometer (PAX405), and a single particle soot photometer (SP2). The average refractory black carbon (rBC) concentration during the campaign was 0.14 µg m−3, representing 3 % of the fine aerosol mass. The measured light absorption was two or more times higher than that of fresh black carbon (BC). Mie theory indicated that the absorption enhancement due to the coating of BC cores by nonrefractory material could explain only part of this absorption enhancement. The role of brown carbon (BrC) and other non-BC light-absorbing material was then investigated. A good correlation (R2=0.76) between the unexplained absorption and the concentration of extremely low volatility organic compounds (ELVOCs) mass was found.

scholarly journals Brown carbon: a significant atmospheric absorber of solar radiation?

2013 ◽  
Vol 13 (17) ◽  
pp. 8607-8621 ◽  
Author(s):  
Y. Feng ◽  
V. Ramanathan ◽  
V. R. Kotamarthi
Keyword(s):  
Organic Carbon ◽  
Solar Radiation ◽  
Black Carbon ◽  
Organic Aerosols ◽  
Transfer Model ◽  
Anthropogenic Aerosols ◽  
Brown Carbon ◽  
Enhanced Absorption ◽  
Aerosol Absorption ◽  
Carbon Aerosols

Abstract. Several recent observational studies have shown organic carbon aerosols to be a significant source of absorption of solar radiation. The absorbing part of organic aerosols is referred to as "brown" carbon (BrC). Using a global chemical transport model and a radiative transfer model, we estimate for the first time the enhanced absorption of solar radiation due to BrC in a global model. The simulated wavelength dependence of aerosol absorption, as measured by the absorption Ångström exponent (AAE), increases from 0.9 for non-absorbing organic carbon to 1.2 (1.0) for strongly (moderately) absorbing BrC. The calculated AAE for the strongly absorbing BrC agrees with AERONET spectral observations at 440–870 nm over most regions but overpredicts for the biomass burning-dominated South America and southern Africa, in which the inclusion of moderately absorbing BrC has better agreement. The resulting aerosol absorption optical depth increases by 18% (3%) at 550 nm and 56% (38%) at 380 nm for strongly (moderately) absorbing BrC. The global simulations suggest that the strongly absorbing BrC contributes up to +0.25 W m−2 or 19% of the absorption by anthropogenic aerosols, while 72% is attributed to black carbon, and 9% is due to sulfate and non-absorbing organic aerosols coated on black carbon. Like black carbon, the absorption of BrC (moderately to strongly) inserts a warming effect at the top of the atmosphere (TOA) (0.04 to 0.11 W m−2), while the effect at the surface is a reduction (−0.06 to −0.14 W m−2). Inclusion of the strongly absorption of BrC in our model causes the direct radiative forcing (global mean) of organic carbon aerosols at the TOA to change from cooling (−0.08 W m−2) to warming (+0.025 W m−2). Over source regions and above clouds, the absorption of BrC is higher and thus can play an important role in photochemistry and the hydrologic cycle.

scholarly journals Aerosol light absorption and the role of extremely low volatility organic compounds

2020 ◽  
Author(s):  
Antonios Tasoglou ◽  
Evangelos Louvaris ◽  
Kalliopi Florou ◽  
Aikaterini Liangou ◽  
Eleni Karnezi ◽  
...  
Keyword(s):  
Black Carbon ◽  
Organic Compounds ◽  
Light Absorption ◽  
Absorption Enhancement ◽  
Scanning Mobility Particle Sizer ◽  
Brown Carbon ◽  
Aerosol Absorption ◽  
Aerosol Mass ◽  
Particle Sizer

Abstract. A month-long set of summertime measurements in a remote area in the Mediterranean is used to quantify aerosol absorption and the role of black and brown carbon. The suite of instruments included a high-resolution Aerosol Mass Spectrometer (HR-ToF-AMS), and a Scanning Mobility Particle Sizer (SMPS) both coupled to a thermodenuder and an aethalometer, a photoacoustic extinctiometer (PAX405), a Multi-Angle Absorption Photometer (MAAP), and a Single Particle Soot Photometer (SP2). The average refractory black carbon (rBC) concentration during the campaign was 0.14 μg m−3, representing 3 % of the fine aerosol mass. The measured light absorption was two or more times higher than that of fresh black carbon (BC). Mie theory indicated that the absorption enhancement due to the coating of BC cores by non-refractory material could explain only part of this absorption enhancement. The role of brown carbon (BrC) and other non-BC light-absorbing material was then investigated. A good correlation (R2 = 0.65) between the unexplained absorption and the concentration of extremely low volatility organic compounds (ELVOCs) mass was found.

scholarly journals Observationally constrained representation of brown carbon emissions from wildfires in a chemical transport model

2022 ◽  
Author(s):  
Soroush E Neyestani ◽  
Rawad Saleh
Keyword(s):  
Black Carbon ◽  
Carbon Emissions ◽  
Transport Model ◽  
Chemical Transport ◽  
Carbonaceous Aerosols ◽  
Chemical Transport Model ◽  
Brown Carbon

The month of August 2015 featured extensive wildfires in the Northwestern U.S. and no significant fires in Alaska and Canada. With the majority of carbonaceous aerosols (CA), including black carbon...

scholarly journals Modeling global radiative effect of brown carbon: A larger heating source in the tropical free troposphere than black carbon

2019 ◽  
Author(s):  
Aoxing Zhang ◽  
Yuhang Wang ◽  
Yuzhong Zhang ◽  
Rodney J. Weber ◽  
Yongjia Song ◽  
...  
Keyword(s):  
Black Carbon ◽  
Biomass Burning ◽  
Radiative Heating ◽  
Environmental Research ◽  
Carbonaceous Aerosols ◽  
Free Troposphere ◽  
Radiative Effect ◽  
Brown Carbon ◽  
Upper Troposphere ◽  
Atmospheric Heating

Abstract. Carbonaceous aerosols significantly affect global radiative forcing and climate through absorption and scattering of sunlight. Black carbon (BC) and brown carbon (BrC) are light-absorbing carbonaceous aerosols. The direct radiative effect (DRE) of BrC is uncertain. A recent study suggests that BrC absorption is comparable to BC in the upper troposphere over biomass burning regions and that the resulting radiative heating tends to stabilize the atmosphere. Yet current climate models do not include proper physical and chemical treatments of BrC. In this study, we derived a BrC global biomass burning emission inventory on the basis of the Global Fire Emissions Database 4 (GFED4), developed a BrC module in the Community Atmosphere Model version 5 (CAM5) of Community Earth System Model (CESM) model, and investigated the photo-bleaching effect and convective transport of BrC on the basis of Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) and Deep Convective Clouds and Chemistry Project (DC-3) measurements. The model simulations of BC were also evaluated using HIAPER (High-Performance Instrumented Airborne Platform for Environmental Research) Pole-to-Pole Observations (HIPPO) measurements. We found that globally BrC is a significant absorber, the DRE of which is 0.10 W/m2, more than 25 % of BC DRE (+0.39 W/m2). Most significantly, model results indicated that BrC atmospheric heating in the tropical mid and upper troposphere is larger than that of BC. The source of tropical BrC is mainly from wildfires, which are more prevalent in the tropical regions than higher latitudes and release much more BrC relative to BC than industrial sources. While BC atmospheric heating is skewed towards northern mid-latitude lower atmosphere, BrC heating is more centered in the tropical free troposphere. The contribution of BrC heating to the Hadley circulation and latitudinal expansion of the tropics is comparable to BC heating.

scholarly journals Satellite-based evidence of wavelength-dependent aerosol absorption in biomass burning smoke inferred from Ozone Monitoring Instrument

2011 ◽  
Vol 11 (20) ◽  
pp. 10541-10551 ◽  
Author(s):  
H. Jethva ◽  
O. Torres
Keyword(s):  
Black Carbon ◽  
Biomass Burning ◽  
Spectral Dependence ◽  
Carbonaceous Aerosol ◽  
Imaginary Component ◽  
Carbonaceous Aerosols ◽  
Ozone Monitoring Instrument ◽  
Monitoring Instrument ◽  
Aerosol Absorption ◽  
Ozone Monitoring

Abstract. We provide satellite-based evidence of the spectral dependence of absorption in biomass burning aerosols over South America using near-UV measurements made by the Ozone Monitoring Instrument (OMI) during 2005–2007. In the current near-UV OMI aerosol algorithm (OMAERUV), it is implicitly assumed that the only absorbing component in carbonaceous aerosols is black carbon whose imaginary component of the refractive index is wavelength independent. With this assumption, OMI-derived aerosol optical depth (AOD) is found to be significantly over-estimated compared to that of AERONET at several sites during intense biomass burning events (August-September). Other well-known sources of error affecting the near-UV method of aerosol retrieval do not explain the large observed AOD discrepancies between the satellite and the ground-based observations. A number of studies have revealed strong spectral dependence in carbonaceous aerosol absorption in the near-UV region suggesting the presence of organic carbon in biomass burning generated aerosols. A sensitivity analysis examining the importance of accounting for the presence of wavelength-dependent aerosol absorption in carbonaceous particles in satellite-based remote sensing was carried out in this work. The results convincingly show that the inclusion of spectrally-dependent aerosol absorption in the radiative transfer calculations leads to a more accurate characterization of the atmospheric load of carbonaceous aerosols. The use of a new set of aerosol models assuming wavelength-dependent aerosol absorption in the near-UV region (Absorption Angstrom Exponent λ−2.5 to −3.0) improved the OMAERUV retrieval results by significantly reducing the AOD bias observed when gray aerosols were assumed. In addition, the new retrieval of single-scattering albedo is in better agreement with those of AERONET within the uncertainties (ΔSSA = ±0.03). The new colored carbonaceous aerosol model was also found to reproduce the ground-based AOD observations over the biomass burning region of central Africa and northern India. Together with demonstrating a significant improvement in the retrieval of aerosol properties from OMI, the present study highlights the greater sensitivity of the near-UV measurements to the varying spectral aerosol absorption. This capability can be explored further for the use in the identification of the black carbon and organics in the biomass burning aerosols.

scholarly journals Relative importance of black carbon, brown carbon, and absorption enhancement from clear coatings in biomass burning emissions

2017 ◽  
Vol 17 (8) ◽  
pp. 5063-5078 ◽  
Author(s):  
Rudra P. Pokhrel ◽  
Eric R. Beamesderfer ◽  
Nick L. Wagner ◽  
Justin M. Langridge ◽  
Daniel A. Lack ◽  
...  
Keyword(s):  
Black Carbon ◽  
Combustion Efficiency ◽  
Absorption Enhancement ◽  
Total Absorption ◽  
Brown Carbon ◽  
Aerosol Absorption ◽  
Wide Range ◽  
Visible Wavelengths ◽  
Aerosol Emissions ◽  
Modified Combustion Efficiency

Abstract. A wide range of globally significant biomass fuels were burned during the fourth Fire Lab at Missoula Experiment (FLAME-4). A multi-channel photoacoustic absorption spectrometer (PAS) measured dry absorption at 405, 532, and 660 nm and thermally denuded (250 °C) absorption at 405 and 660 nm. Absorption coefficients were broken into contributions from black carbon (BC), brown carbon (BrC), and lensing following three different methodologies, with one extreme being a method that assumes the thermal denuder effectively removes organics and the other extreme being a method based on the assumption that black carbon (BC) has an Ångström exponent of unity. The methodologies employed provide ranges of potential importance of BrC to absorption but, on average, there was a difference of a factor of 2 in the ratio of the fraction of absorption attributable to BrC estimated by the two methods. BrC absorption at shorter visible wavelengths is of equal or greater importance to that of BC, with maximum contributions of up to 92 % of total aerosol absorption at 405 nm and up to 58 % of total absorption at 532 nm. Lensing is estimated to contribute a maximum of 30 % of total absorption, but typically contributes much less than this. Absorption enhancements and the estimated fraction of absorption from BrC show good correlation with the elemental-carbon-to-organic-carbon ratio (EC ∕ OC) of emitted aerosols and weaker correlation with the modified combustion efficiency (MCE). Previous studies have shown that BrC grows darker (larger imaginary refractive index) as the ratio of black to organic aerosol (OA) mass increases. This study is consistent with those findings but also demonstrates that the fraction of total absorption attributable to BrC shows the opposite trend: increasing as the organic fraction of aerosol emissions increases and the EC ∕ OC ratio decreases.

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