scholarly journals Markedly enhanced absorption and direct radiative forcing of black carbon under polluted urban environments

2016 ◽  
Vol 113 (16) ◽  
pp. 4266-4271 ◽  
Author(s):  
Jianfei Peng ◽  
Min Hu ◽  
Song Guo ◽  
Zhuofei Du ◽  
Jing Zheng ◽  
...  
Keyword(s):  
Developing Countries ◽  
Black Carbon ◽  
Radiative Forcing ◽  
Urban Environments ◽  
Absorption Enhancement ◽  
Ambient Conditions ◽  
Climatic Impact ◽  
Atmospheric Aging ◽  
Enhanced Absorption ◽  
Direct Radiative Forcing

Black carbon (BC) exerts profound impacts on air quality and climate because of its high absorption cross-section over a broad range of electromagnetic spectra, but the current results on absorption enhancement of BC particles during atmospheric aging remain conflicting. Here, we quantified the aging and variation in the optical properties of BC particles under ambient conditions in Beijing, China, and Houston, United States, using a novel environmental chamber approach. BC aging exhibits two distinct stages, i.e., initial transformation from a fractal to spherical morphology with little absorption variation and subsequent growth of fully compact particles with a large absorption enhancement. The timescales to achieve complete morphology modification and an absorption amplification factor of 2.4 for BC particles are estimated to be 2.3 h and 4.6 h, respectively, in Beijing, compared with 9 h and 18 h, respectively, in Houston. Our findings indicate that BC under polluted urban environments could play an essential role in pollution development and contribute importantly to large positive radiative forcing. The variation in direct radiative forcing is dependent on the rate and timescale of BC aging, with a clear distinction between urban cities in developed and developing countries, i.e., a higher climatic impact in more polluted environments. We suggest that mediation in BC emissions achieves a cobenefit in simultaneously controlling air pollution and protecting climate, especially for developing countries.

scholarly journals Exploiting simultaneous observational constraints on mass and absorption to estimate the global direct radiative forcing of black carbon and brown carbon

2014 ◽  
Vol 14 (20) ◽  
pp. 10989-11010 ◽  
Author(s):  
X. Wang ◽  
C. L. Heald ◽  
D. A. Ridley ◽  
J. P. Schwarz ◽  
J. R. Spackman ◽  
...  
Keyword(s):  
Optical Properties ◽  
Black Carbon ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Model Simulation ◽  
Anthropogenic Sources ◽  
Absorption Enhancement ◽  
Brown Carbon ◽  
Direct Radiative Forcing ◽  
Improved Model

Abstract. Atmospheric black carbon (BC) is a leading climate warming agent, yet uncertainties on the global direct radiative forcing (DRF) remain large. Here we expand a global model simulation (GEOS-Chem) of BC to include the absorption enhancement associated with BC coating and separately treat both the aging and physical properties of fossil-fuel and biomass-burning BC. In addition we develop a global simulation of brown carbon (BrC) from both secondary (aromatic) and primary (biomass burning and biofuel) sources. The global mean lifetime of BC in this simulation (4.4 days) is substantially lower compared to the AeroCom I model means (7.3 days), and as a result, this model captures both the mass concentrations measured in near-source airborne field campaigns (ARCTAS, EUCAARI) and surface sites within 30%, and in remote regions (HIPPO) within a factor of 2. We show that the new BC optical properties together with the inclusion of BrC reduces the model bias in absorption aerosol optical depth (AAOD) at multiple wavelengths by more than 50% at AERONET sites worldwide. However our improved model still underestimates AAOD by a factor of 1.4 to 2.8 regionally, with the largest underestimates in regions influenced by fire. Using the RRTMG model integrated with GEOS-Chem we estimate that the all-sky top-of-atmosphere DRF of BC is +0.13 Wm−2 (0.08 Wm−2 from anthropogenic sources and 0.05 Wm−2 from biomass burning). If we scale our model to match AERONET AAOD observations we estimate the DRF of BC is +0.21 Wm−2, with an additional +0.11 Wm−2 of warming from BrC. Uncertainties in size, optical properties, observations, and emissions suggest an overall uncertainty in BC DRF of −80%/+140%. Our estimates are at the lower end of the 0.2–1.0 Wm−2 range from previous studies, and substantially less than the +0.6 Wm−2 DRF estimated in the IPCC 5th Assessment Report. We suggest that the DRF of BC has previously been overestimated due to the overestimation of the BC lifetime (including the effect on the vertical profile) and the incorrect attribution of BrC absorption to BC.

scholarly journals Exploiting simultaneous observational constraints on mass and absorption to estimate the global direct radiative forcing of black carbon and brown carbon

2014 ◽  
Vol 14 (11) ◽  
pp. 17527-17583 ◽  
Author(s):  
X. Wang ◽  
C. L. Heald ◽  
D. A. Ridley ◽  
J. P. Schwarz ◽  
J. R. Spackman ◽  
...  
Keyword(s):  
Optical Properties ◽  
Black Carbon ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Model Simulation ◽  
Anthropogenic Sources ◽  
Absorption Enhancement ◽  
Brown Carbon ◽  
Direct Radiative Forcing ◽  
Improved Model

Abstract. Atmospheric black carbon (BC) is a leading climate warming agent, yet uncertainties on the global direct radiative forcing (DRF) remain large. Here we expand a global model simulation (GEOS-Chem) of BC to include the absorption enhancement associated with BC coating and separately treat both the aging and physical properties of fossil fuel and biomass burning BC. In addition we develop a global simulation of Brown Carbon (BrC) from both secondary (aromatic) and primary (biomass burning and biofuel) sources. The global mean lifetime of BC in this simulation (4.4 days) is substantially lower compared to the AeroCom I model means (7.3 days), and as a result, this model captures both the mass concentrations measured in near-source airborne field campaigns (ARCTAS, EUCAARI) and surface sites within 30%, and in remote regions (HIPPO) within a factor of two. We show that the new BC optical properties together with the inclusion of BrC reduces the model bias in Absorption Aerosol Optical Depth (AAOD) at multiple wavelengths by more than 50% at AERONET sites worldwide. However our improved model still underestimates AAOD by a factor of 1.4 to 2.8 regionally, with largest underestimates in regions influenced by fire. Using the RRTMG model integrated with GEOS-Chem we estimate that the all-sky top-of-atmosphere DRF of BC is +0.13 W m−2 (0.08 W m−2 from anthropogenic sources and 0.05 W m−2 from biomass burning). If we scale our model to match AERONET AAOD observations we estimate the DRF of BC is +0.21 W m−2, with an additional +0.11 W m−2 of warming from BrC. Uncertainties in size, optical properties, observations, and emissions suggest an overall uncertainty in BC DRF of −80% / +140%. Our estimates are at the lower end of the 0.2–1.0 W m−2 range from previous studies, and substantially less than the +0.6 W m−2 DRF estimated in the IPCC 5th Assessment Report. We suggest that the DRF of BC has previously been overestimated due to the overestimation of the BC lifetime and the incorrect attribution of BrC absorption to BC.

scholarly journals Impacts of East Asian Summer and Winter Monsoon on Interannual Variations of Mass Concentrations and Direct Radiative Forcing of Black Carbon over Eastern China

2016 ◽  
Author(s):  
Yu Hao Mao ◽  
Hong Liao
Keyword(s):  
Black Carbon ◽  
Radiative Forcing ◽  
Southern China ◽  
East Asian ◽  
Eastern China ◽  
Northern China ◽  
Winter Monsoon ◽  
Interannual Variations ◽  
Direct Radiative Forcing ◽  
Asian Summer

Abstract. We applied a global three-dimensional chemical transport model (GEOS-Chem) to examine the impacts of the East Asian monsoon on the interannual variations of mass concentrations and direct radiative forcing (DRF) of black carbon (BC) over eastern China (110–125° E, 20–45° N). With emissions fixed at the year 2010 levels, model simulations were driven by the Goddard Earth Observing System (GEOS-4) meteorological fields for 1986–2006 and the Modern Era Retrospective-analysis for Research and Applications (MERRA) meteorological fields for 1980–2010. During the period of 1986–2006, simulated JJA and DJF surface BC concentrations were higher in MERRA than in GEOS-4 by 0.30 µg m−3 (44 %) and 0.77 µg m−3 (54 %), respectively, because of the generally weaker precipitation in MERRA. We found that the strength of the East Asian summer monsoon (EASM, (East Asian winter monsoon, EAWM)) negatively correlated with simulated JJA (DJF) surface BC concentrations (r = –0.7 (–0.7) in GEOS-4 and –0.4 (–0.7) in MERRA), mainly by the changes in atmospheric circulation. Relative to the five strongest EASM years, simulated JJA surface BC concentrations in the five weakest monsoon years were higher over northern China (110–125° E, 28–45° N) by 0.04–0.09 µg m−3 (3–11 %), but lower over southern China (110–125° E, 20–27° N) by 0.03–0.04 µg m−3 (10–11 %). Compared to the five strongest EAWM years, simulated DJF surface BC concentrations in the five weakest monsoon years were higher by 0.13–0.15 µg m−3 (5–8 %) in northern China and by 0.04–0.10 µg m−3 (3–12 %) in southern China. The resulting JJA (DJF) mean all-sky DRF of BC at the top of the atmosphere were 0.04 W m−2 (3 %, (0.03 W m−2, 2 %)) higher in northern China but 0.06 W m−2 (14 %, (0.03 W m−2, 3 %)) lower in southern China. In the weakest monsoon years, the weaker vertical convection led to the lower BC concentrations above 1–2 km in southern China, and therefore the lower BC DRF in the region. The differences in vertical profiles of BC between the weakest and strongest EASM years (1998–1997) and EAWM years (1990–1996) reached up to –0.09 µg m−3 (–46 %) and –0.08 µg m−3 (–11 %) at 1–2 km in eastern China.

scholarly journals Impact of brown and clear carbon on light absorption enhancement, single scatter albedo and absorption wavelength dependence of black carbon

2010 ◽  
Vol 10 (9) ◽  
pp. 4207-4220 ◽  
Author(s):  
D. A. Lack ◽  
C. D. Cappa
Keyword(s):  
Black Carbon ◽  
Light Absorption ◽  
Radiative Forcing ◽  
Large Scale ◽  
Wavelength Dependence ◽  
Absorption Enhancement ◽  
Core Shell ◽  
Enhancement Effect ◽  
Visible Radiation ◽  
Single Scatter

Abstract. The presence of clear coatings on atmospheric black carbon (BC) particles is known to enhance the magnitude of light absorption by the BC cores. Based on calculations using core/shell Mie theory, we demonstrate that the enhancement of light absorption (EAbs) by atmospheric black carbon (BC) when it is coated in mildly absorbing material (CBrown) is reduced relative to the enhancement induced by non-absorbing coatings (CClear). This reduction, sensitive to both the CBrown coating thickness and imaginary refractive index (RI), can be up to 50% for 400 nm radiation and 25% averaged across the visible radiation spectrum for reasonable core/shell diameters. The enhanced direct radiative forcing possible due to the enhancement effect of CClear is therefore reduced if the coating is absorbing. Additionally, the need to explicitly treat BC as an internal, as opposed to external, mixture with CBrown is shown to be important to the calculated single scatter albedo only when models treat BC as large spherical cores (>50 nm). For smaller BC cores (or fractal agglomerates) consideration of the BC and CBrown as an external mixture leads to relatively small errors in the particle single scatter albedo of <0.03. It has often been assumed that observation of an absorption Angström exponent (AAE)>1 indicates absorption by a non-BC aerosol. Here, it is shown that BC cores coated in CClear can reasonably have an AAE of up to 1.6, a result that complicates the attribution of observed light absorption to CBrown within ambient particles. However, an AAE<1.6 does not exclude the possibility of CBrown; rather CBrown cannot be confidently assigned unless AAE>1.6. Comparison of these model results to various ambient AAE measurements demonstrates that large-scale attribution of CBrown is a challenging task using current in-situ measurement methods. We suggest that coincident measurements of particle core and shell sizes along with the AAE may be necessary to distinguish absorbing and non-absorbing OC.

Experimental evidence of the lensing effect suppression for atmospheric black carbon containing brown coatings

2020 ◽  
Author(s):  
Vaios Moschos ◽  
Martin Gysel-Beer ◽  
Robin L. Modini ◽  
Joel C. Corbin ◽  
Dario Massabò ◽  
...  
Keyword(s):  
Black Carbon ◽  
Radiative Forcing ◽  
Wavelength Dependence ◽  
Chem Phys ◽  
Absorption Enhancement ◽  
Visible Spectroscopy ◽  
Scanning Mobility Particle Sizer ◽  
Absorption Data ◽  
Brown Carbon ◽  
Aerosol Radiative Forcing

&lt;p&gt;Accounting for the wavelength- and source-dependent optical absorption properties of the abundant light-absorbing organic (brown) carbon (BrC) and the mixing state of atmospheric black carbon (BC) are essential to reduce the large uncertainty in aerosol radiative forcing.&amp;#160;Estimation of BrC absorption online by subtraction is highly uncertain and may be biased if not decoupled from the potential BC absorption enhancement (lensing) due to non-refractory (organic and inorganic) coating acquisition.&lt;/p&gt;&lt;p&gt;Here, the reported total particulate absorption is based on long-term, filter-based seven-wavelength Aethalometer (AE33 model) data, corrected for multiple scattering effects with Multi-Wavelength Absorbance Analyzer (5&amp;#955; MWAA) measurements. Using ultraviolet-visible spectroscopy absorbance measurements along with particle size distributions obtained by a scanning mobility particle sizer, we have conducted Mie calculations to assess the importance of source-specific extractable particulate BrC (Moschos et al., 2018) versus BC absorption.&lt;/p&gt;&lt;p&gt;For the species-specific optical closure, the wavelength dependence of bare BC absorption is estimated using MWAA measurements upon successive filter extractions to remove the influence of BrC/coatings. The lensing contribution, supported by observations from field-emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, is estimated at longer wavelengths using a refined proxy for the BC coating thickness. The approach is validated independently by applying a novel positive matrix factorization-based approach on the calibrated total AE33 absorption data.&lt;/p&gt;&lt;p&gt;Based on the observational constraints established in this study, we demonstrate for various distinct case studies that the interplay between lensing and BrC absorption results in lower than expected BC absorption at shorter wavelengths. This indicates that the volume additivity assumption is not valid for particulate absorption by internally mixed heterogeneous atmospheric aerosol populations. These comprehensive experimental analyses verify the BC lensing suppression predicted for simplified core-shell structures containing moderately absorbing BrC (Lack &amp; Cappa, 2010). The implications discussed in this work are relevant for co-emitted species from biomass burning or aged plumes with high BrC to BC mass/absorption ratio.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Moschos, V., Kumar, N. K., Daellenbach, K. R., Baltensperger, U., Pr&amp;#233;v&amp;#244;t, A. S. H., and El Haddad, I.: Source apportionment of brown carbon absorption by coupling ultraviolet-visible spectroscopy with aerosol mass spectrometry, Environ. Sci. Tech. Lett., 5, 302-308, https://doi.org/10.1021/acs.estlett.8b00118, 2018.&lt;/p&gt;&lt;p&gt;Lack, D. A. and Cappa, C. D.: Impact of brown and clear carbon on light absorption enhancement, single scatter albedo and absorption wavelength dependence of black carbon, Atmos. Chem. Phys., 10, 4207&amp;#8211;4220, https://doi.org/10.5194/acp-10-4207-2010, 2010.&lt;/p&gt;

Distribution and direct radiative forcing of black carbon aerosols over Korean Peninsula

2012 ◽  
Vol 58 ◽  
pp. 45-55 ◽  
Author(s):  
Min Young Kim ◽  
Seung-Bok Lee ◽  
Gwi-Nam Bae ◽  
Seung Shik Park ◽  
Kyung Man Han ◽  
...  
Keyword(s):  
Black Carbon ◽  
Korean Peninsula ◽  
Radiative Forcing ◽  
Direct Radiative Forcing ◽  
Carbon Aerosols ◽  
Black Carbon Aerosols
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