scholarly journals Scattering and Radiative Properties of Morphologically Complex Carbonaceous Aerosols: A Systematic Modeling Study

2018 ◽  
Vol 10 (10) ◽  
pp. 1634 ◽  
Author(s):  
Li Liu ◽  
Michael Mishchenko
Keyword(s):  
Black Carbon ◽  
Radiative Forcing ◽  
Accurate Estimate ◽  
Coating Material ◽  
Radiative Properties ◽  
Absorption Enhancement ◽  
Carbonaceous Aerosols ◽  
Carbonaceous Particles ◽  
Full Characterization ◽  
Linear Depolarization Ratio

This paper provides a thorough modeling-based overview of the scattering and radiative properties of a wide variety of morphologically complex carbonaceous aerosols. Using the numerically-exact superposition T-matrix method, we examine the absorption enhancement, absorption Ångström exponent (AAE), backscattering linear depolarization ratio (LDR), and scattering matrix elements of black-carbon aerosols with 11 different model morphologies ranging from bare soot to completely embedded soot–sulfate and soot–brown carbon mixtures. Our size-averaged results show that fluffy soot particles absorb more light than compact bare-soot clusters. For the same amount of absorbing material, the absorption cross section of internally mixed soot can be more than twice that of bare soot. Absorption increases as soot accumulates more coating material and can become saturated. The absorption enhancement is affected by particle size, morphology, wavelength, and the amount of coating. We refute the conventional belief that all carbonaceous aerosols have AAEs close to 1.0. Although LDRs caused by bare soot and certain carbonaceous particles are rather weak, LDRs generated by other soot-containing aerosols can reproduce strong depolarization measured by Burton et al. for aged smoke. We demonstrate that multi-wavelength LDR measurements can be used to identify the presence of morphologically complex carbonaceous particles, although additional observations can be needed for full characterization. Our results show that optical constants of the host/coating material can significantly influence the scattering and absorption properties of soot-containing aerosols to the extent of changing the sign of linear polarization. We conclude that for an accurate estimate of black-carbon radiative forcing, one must take into account the complex morphologies of carbonaceous aerosols in remote sensing studies as well as in atmospheric radiation computations.

scholarly journals Effects of mixing state on optical and radiative properties of black carbon in the European Arctic

2018 ◽  
Author(s):  
Marco Zanatta ◽  
Paolo Laj ◽  
Martin Gysel ◽  
Urs Baltensperger ◽  
Stergios Vratolis ◽  
...  
Keyword(s):  
Black Carbon ◽  
Radiative Forcing ◽  
Particle Diameter ◽  
Arctic Region ◽  
Climate Impacts ◽  
Radiative Properties ◽  
The Arctic ◽  
Absorption Enhancement ◽  
Equivalent Diameter ◽  
Mixing State

Abstract. Atmospheric aging promotes internal mixing of black carbon (BC) leading to an enhancement of light absorption and radiative forcing. The relationship between BC mixing state and consequent absorption enhancement was never estimated for BC found in the Arctic region. In the present work, we aim to quantify the absorption enhancement and its impact on radiative forcing as a function of microphysical properties and mixing state of BC observed in-situ at the Zeppelin Arctic station (78° N) in the spring of 2012 during the CLIMSLIP (Climate impacts of short-lived pollutants in the Arctic) project. Single particle soot photometer (SP2) measurements showed a mean mass concentration of refractory black carbon (rBC) of 39 ng m−3, while the rBC mass size distribution was of log-normal shape peaking at an rBC mass equivalent diameter (DrBC) of around 240 nm. On average, the number fraction of particles containing a BC core with DrBC > 80 nm was less than 5 % in the size range (overall optical particle diameter) from 150–500 nm. The BC cores were internally mixed with other particulate matter. The median coating thickness of BC cores with 220 nm 

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 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;

Derivation of Optical Properties of Carbonaceous Aerosols by Monochromated Electron Energy-Loss Spectroscopy

2014 ◽  
Vol 20 (3) ◽  
pp. 748-759 ◽  
Author(s):  
Jiangtao Zhu ◽  
Peter A. Crozier ◽  
Peter Ercius ◽  
James R. Anderson
Keyword(s):  
Optical Properties ◽  
Energy Loss ◽  
Electron Energy ◽  
Amorphous Carbon ◽  
Electron Energy Loss Spectroscopy ◽  
Radiative Forcing ◽  
Accurate Determination ◽  
Carbonaceous Aerosols ◽  
Carbonaceous Particles ◽  
Electron Energy Loss

AbstractMonochromated electron energy-loss spectroscopy (EELS) is employed to determine the optical properties of carbonaceous aerosols from the infrared to the ultraviolet region of the spectrum. It is essential to determine their optical properties to understand their accurate contribution to radiative forcing for climate change. The influence of surface and interface plasmon effects on the accuracy of dielectric data determined from EELS is discussed. Our measurements show that the standard thin film formulation of Kramers−Kronig analysis can be employed to make accurate determination of the dielectric function for carbonaceous particles down to about 40 nm in size. The complex refractive indices of graphitic and amorphous carbon spherules found in the atmosphere were determined over the wavelength range 200–1,200 nm. The graphitic carbon was strongly absorbing black carbon, whereas the amorphous carbon shows a more weakly absorbing brown carbon profile. The EELS approach provides an important tool for exploring the variation in optical properties of atmospheric carbon.

scholarly journals Enhanced solar energy absorption by internally-mixed black carbon in snow grains

2012 ◽  
Vol 12 (1) ◽  
pp. 2057-2113 ◽  
Author(s):  
M. G. Flanner ◽  
X. Liu ◽  
C. Zhou ◽  
J. E. Penner
Keyword(s):  
Sea Ice ◽  
Black Carbon ◽  
Radiative Forcing ◽  
Climate Model ◽  
Volume Fraction ◽  
Global Climate ◽  
Global Climate Model ◽  
Absorption Enhancement ◽  
Liquid Droplets ◽  
Vapor Transfer

Abstract. Here we explore light absorption by snowpack containing black carbon (BC) particles residing within ice grains. Basic considerations of particle volumes and BC/snow mass concentrations show that there are generally 0.05–109 BC particles for each ice grain. This suggests that internal BC is likely distributed as multiple inclusions within ice grains, and thus the dynamic effective medium approximation (DEMA) (Chýlek and Srivastava, 1983) is a more appropriate optical representation for BC/ice composites than coated-sphere or standard mixing approximations. DEMA calculations show that the 460 nm absorption cross-section of BC/ice composites, normalized to the mass of BC, is typically enhanced by factors of 1.8–2.1 relative to interstitial BC. BC effective radius is the dominant cause of variation in this enhancement, compared with ice grain size and BC volume fraction. We apply two atmospheric aerosol models that simulate interstitial and within-hydrometeor BC lifecycles. Although only ~2% of the atmospheric BC burden is cloud-borne, 71–83% of the BC deposited to global snow and sea-ice surfaces occurs within hydrometeors. Key processes responsible for within-snow BC deposition are development of hydrophilic coatings on BC, activation of liquid droplets, and subsequent snow formation through riming or ice nucleation by other species and aggregation/accretion of ice particles. Applying deposition fields from these aerosol models in offline snow and sea-ice simulations, we calculate that 32–73% of BC in global surface snow resides within ice grains. This fraction is smaller than the within-hydrometeor deposition fraction because meltwater flux preferentially removes internal BC, while sublimation and freezing within snowpack expose internal BC. Incorporating the DEMA into a global climate model, we simulate increases in BC/snow radiative forcing of 43–86%, relative to scenarios that apply external optical properties to all BC. We show that snow metamorphism driven by diffusive vapor transfer likely proceeds too slowly to alter the mass of internal BC while it is radiatively active, but neglected processes like wind pumping and convection may play much larger roles. These results suggest that a large portion of BC in surface snowpack may reside within ice grains and increase BC/snow radiative forcing, although measurements to evaluate this are lacking. Finally, previous studies of BC/snow forcing that neglected this absorption enhancement are not necessarily biased low, because of application of absorption-enhancing sulfate coatings to hydrophilic BC, neglect of coincident absorption by dust in snow, and implicit treatment of cloud-borne BC resulting in longer-range transport.

Predicting the Optical Properties of Arbitrarily Shaped Black Carbon Aerosols with Graph Neural Networks

2021 ◽  
Author(s):  
Kara D. Lamb ◽  
Pierre Gentine
Keyword(s):  
Remote Sensing ◽  
Optical Properties ◽  
Black Carbon ◽  
Radiative Forcing ◽  
Training Data ◽  
Radiative Properties ◽  
Training Dataset ◽  
Small Scale ◽  
Atmospheric Models ◽  
Fractal Aggregates

&lt;p&gt;Aerosols sourced from combustion such as black carbon (BC) are important short-lived climate forcers whose direct radiative forcing and atmospheric lifetime depend on their morphology. These aerosols are typically fractal aggregates consisting of ~20-80 nm spheres. This complex morphology makes modeling their optical properties difficult, contributing to uncertainty in both their direct and indirect climate effects. Accurate and fast calculations of BC optical properties are needed for remote sensing inversions and for radiative forcing calculations in atmospheric models, but current methods to accurately calculate the optical properties of these aerosols such as the multi-sphere T-matrix method or generalized multiple-particle Mie Theory are computationally expensive and must be compiled in extensive data-bases off-line and then used as a look-up table. Recent advances in machine learning approaches have applied the graph convolutional neural network (GCN) to various physical science applications, demonstrating skill in generalizing beyond initial training data by exploiting and learning internal properties and interactions inherent to the larger system. Here we demonstrate for the first time that a GCN trained to predict the optical properties of numerically-generated BC fractal aggregates can accurately generalize to arbitrarily shaped aerosol particles, even over much larger aggregates than in the training dataset, providing a fast and accurate method to calculate aerosol optical properties in atmospheric models and for observational retrievals. This approach could be integrated into atmospheric models or remote sensing inversions to more realistically predict the physical properties of arbitrarily-shaped aerosol and cloud particles. In addition, GCN&amp;#8217;s can be used to gain physical intuition on the relationship between large-scale properties (here of the radiative properties of aerosols) and small-scale interactions (here of the spheres&amp;#8217; positions and their interactions).&lt;/p&gt;

scholarly journals Wintertime aerosol optical and radiative properties in the Kathmandu Valley during the SusKat-ABC field campaign

2017 ◽  
Vol 17 (20) ◽  
pp. 12617-12632 ◽  
Author(s):  
Chaeyoon Cho ◽  
Sang-Woo Kim ◽  
Maheswar Rupakheti ◽  
Jin-Soo Park ◽  
Arnico Panday ◽  
...  
Keyword(s):  
Black Carbon ◽  
Urban Areas ◽  
Regional Scale ◽  
Temperature Drop ◽  
Absorption Efficiency ◽  
Radiative Properties ◽  
Kathmandu Valley ◽  
Carbonaceous Aerosols ◽  
Brick Kilns ◽  
Aerosol Mass

Abstract. Particulate air pollution in the Kathmandu Valley has reached severe levels that are mainly due to uncontrolled emissions and the location of the urban area in a bowl-shaped basin with associated local wind circulations. The AERONET measurements from December 2012 to August 2014 revealed a mean aerosol optical depth (AOD) of approximately 0.30 at 675 nm during winter, which is similar to that of the post-monsoon but half of that of the pre-monsoon AOD (0.63). The distinct seasonal variations are closely related to regional-scale monsoon circulations over South Asia and emissions in the Kathmandu Valley. During the SusKat-ABC campaign (December 2012–February 2013), a noticeable increase in both aerosol scattering (σs; 313  →  577 Mm−1 at 550 nm) and absorption (σa; 98  →  145 Mm−1 at 520 nm) coefficients occurred before and after 4 January 2013. This can be attributed to the increase in wood-burned fires due to a temperature drop and the start of firing at nearby brick kilns. The σs value in the Kathmandu Valley was a factor of 0.5 lower than that in polluted cities in India. The σa value in the Kathmandu Valley was approximately 2 times higher than that at severely polluted urban sites in India. The aerosol mass scattering efficiency of 2.6 m2 g−1 from PM10 measurements in the Kathmandu Valley is similar to that reported in urban areas. However, the aerosol mass absorption efficiency was determined to be 11 m2 g−1 from PM10 measurements, which is higher than that reported in the literature for pure soot particles (7.5 ± 1.2 m2 g−1). This might be due to the fact that most of the carbonaceous aerosols in the Kathmandu Valley were thought to be mostly externally mixed with other aerosols under dry conditions due to a short travel time from their sources. The σs and σa values and the equivalent black carbon (EBC) mass concentration reached up to 757 Mm−1, 224 Mm−1, and 29 µg m−3 at 08:00 LST (local standard time), respectively but decreased dramatically during the daytime (09:00–18:00 LST), to one-quarter of the morning average (06:00–09:00 LST) due to the development of valley winds and an atmospheric bounder layer. The σs and σa values and the EBC concentration remained almost constant during the night at the levels of 410 Mm−1, 130 Mm−1, and 17 µg m−3, respectively. The average aerosol direct radiative forcings over the intensive measurement period were estimated to be −6.9 ± 1.4 W m−2 (top of the atmosphere) and −20.8 ± 4.6 W m−2 (surface). Therefore, the high atmospheric forcing (i.e., 13.9 ± 3.6 W m−2) and forcing efficiency (74.8 ± 24.2 W m−2 τ−1) can be attributed to the high portion of light-absorbing aerosols in the Kathmandu Valley, as indicated by the high black carbon (or elemental carbon) to sulphate ratio (1.5 ± 1.1).

scholarly journals Variation of the radiative properties during black carbon aging: theoretical and experimental intercomparison

2015 ◽  
Vol 15 (20) ◽  
pp. 11967-11980 ◽  
Author(s):  
C. He ◽  
K.-N. Liou ◽  
Y. Takano ◽  
R. Zhang ◽  
M. Levy Zamora ◽  
...  
Keyword(s):  
Black Carbon ◽  
Cross Sections ◽  
Climate Models ◽  
Theoretical Calculations ◽  
Accurate Estimate ◽  
Radiative Properties ◽  
Sensitivity Analyses ◽  
Hygroscopic Growth ◽  
Scattering Cross ◽  
Scattering Cross Sections

Abstract. A theoretical black carbon (BC) aging model is developed to account for three typical evolution stages, namely, freshly emitted aggregates, BC coated by soluble material, and BC particles undergoing further hygroscopic growth. The geometric-optics surface-wave (GOS) approach is employed to compute the BC single-scattering properties at each aging stage, which are subsequently compared with laboratory measurements. Theoretical calculations are consistent with measurements in extinction and absorption cross sections for fresh BC aggregates with different BC sizes (i.e., mobility diameters of 155, 245, and 320 nm), with differences of ≤ 25 %. The measured optical cross sections for BC coated by sulfuric acid and for that undergoing further hygroscopic growth are generally captured (differences < 30 %) by theoretical calculations using a concentric core-shell structure, with an overestimate in extinction and absorption of the smallest BC size and an underestimate in scattering of the largest BC size. We find that the absorption and scattering cross sections of fresh BC aggregates vary by 20–40 and 50–65 %, respectively, due to the use of upper (1.95–0.79i) and lower (1.75–0.63i) bounds of BC refractive index, while the variations are < 20 % in absorption and < 50 % in scattering in the case of coated BC particles. Sensitivity analyses of the BC morphology show that the optical properties of fresh BC aggregates are more sensitive to fractal dimension than primary spherule size. The absorption and scattering cross sections of coated BC particles vary by more than a factor of 2 due to different coating structures. We find an increase of 20–250 % in absorption and a factor of 3–15 in scattering during aging, significantly depending on coating morphology and aging stages. This study suggests that an accurate estimate of BC radiative effects requires the incorporation of a dynamic BC aging process that accounts for realistic coating structures in climate models.

scholarly journals The Semidirect Aerosol Effect: Comparison of a Single-Column Model with Large Eddy Simulation for Marine Stratocumulus

2005 ◽  
Vol 18 (1) ◽  
pp. 119-130 ◽  
Author(s):  
B. T. Johnson
Keyword(s):  
Boundary Layer ◽  
Black Carbon ◽  
Radiative Forcing ◽  
General Circulation ◽  
Radiative Properties ◽  
Aerosol Effect ◽  
Large Eddy ◽  
Single Column ◽  
Carbon Aerosols ◽  
Black Carbon Aerosols

Abstract Large eddy simulations (LES) show that the presence of black carbon aerosols in marine boundary layers leads to a marked reduction of stratocumulus liquid water path (LWP) by heating the cloud layer and suppressing convection in the boundary layer. The reduction of LWP leads to a positive radiative forcing known as the semidirect effect. In this study LES results are compared with results from the National Center for Atmospheric Research (NCAR) Single-Column Community Climate Model (SCCM). The SCCM represents clouds and boundary layer processes through simple parameterization schemes that are typical of general circulation models (GCMs) used for climate experiments. In a case study in which black carbon aerosols were introduced in a stratocumulus-capped boundary layer the SCCM gave a semidirect aerosol radiative forcing that was a factor of 5 smaller than the value obtained from the LES. The cloud response to absorbing aerosols was underestimated because of the way that cloud cover and cloud radiative properties were parameterized in the SCCM. Furthermore, the SCCM gave a poor representation of processes, such as entrainment and boundary layer decoupling, that are crucial to determining stratocumulus LWP. This study shows that GCMs may not include all the physical processes necessary to adequately capture the semidirect aerosol effect. Previous GCM estimates of the semidirect effect that have incorporated simple cloud parameterizations should, therefore, be treated with some caution.

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