Black Carbon Inclusions Research Articles

Absorption properties by irregularly shaped particles with inclusions at visible and near-infrared wavelength regions

The absorption properties of snow and ice particles containing impurities such as black carbon (BC) and mineral dust (DS) were investigated using the geometrical optics approximation method (GOM). This study focuses on analyzing the single scattering co-albedo (SSCA) characteristics of non-spherical particles, aiming to enhance the interpretation of radiation observations in snow and ice regions. Particle sizes were varied (rva=50,200 and 500μm) and two types of inclusions (1 ppmw of BC and 100 ppmw DS) were considered. Significant differences in SSCA, ranging from one to two orders of magnitude were observed at λ=0.5μm between the “homogeneous model” with effective medium approximation method (EMA) and the “inhomogeneous model” with 50 BC inclusions. Similarly, differences of a factor of 2 to 4 were found for DS with 100 ppmw at λ=0.5μm and BC with 1 ppmw at λ=0.875μm. To bridge intermediate SSCA values between these models, we propose an “inhomogeneous model with EMA”, introducing two parameters to account for impurity concentration and inclusion aggregation. Our findings highlight the importance of selecting appropriate single scattering calculation methods in the analysis of observation data, particularly when dealing with BC impurity with significant absorption characteristics. This research contributes to a deeper understanding of solar radiation absorption in snow and ice regions, with potential implications for the optical remote sensing of snow and ice and climate modeling studies.

Urban gardens in Antiquity: The case of Gerasa/Jerash in Jordan

In the Eastern Mediterranean, where some of the earliest known urban cities are located, relatively little is known about urban soils in archaeological contexts. Red Mediterranean Soil (RMS) is a hallmark of the Mediterranean region while the impact of long-term urbanization on RMS material is understudied. In this article we present evidence of RMS from the longue durée cityscape of Jerash, Jordan, to determine how humans have used, modified and impacted RMS material in an urban context. Thin-sections were made of twelve RMS samples, and micromorphological studies on several in-situ but disturbed soils adjacent to bedrock were conducted, spanning the initial surface soil disturbances in the Hellenistic and Roman period occupation, as well as transported RMS material spanning the Roman through Umayyad periods (until the earthquake of 749 CE). We compared the on-site inner-urban red soils to natural RMS in the area and found that some characteristics reflect their origin in the Pleistocene soils, while other traits reflect human impact related to urban activities. The majority of the on-site samples contained evidence comparable to modern centers, including changes of structure, texture, inclusions, as well as high levels of contamination of heavy metals and phosphorus (P), which combined are strong signs of urban activity. Evidence including textural pedofeatures, fragmented peds, mixed fabrics, sorting of silt-sized material likely reflect the use of RMS in urban gardens and cultivation. Black carbon inclusions within the fabric contain evidence for burning of organic matter in connection with various anthropogenic activities, likely re-dispersed via aeolian and water erosion processes. Heavy metal enrichments, which are associated with production and artisanal activities, may also have been disseminated by both aeolian and surface water processes, possibly in conjunction with irrigation undertaken with polluted water. Contrasting soil fabrics and inclusion features observed in thin section together with elemental analayses characterizes the nature of urban cultivation in its environmental context at Jerash, where city life was maintained for over 800 years. With cultivated soils in urban areas increasingly evidenced in archaeological stratigraphies from different regions of the world, our approach offers new insight into the vital contributions that these soils and their management has made to the food security, resilience and longevity of early city life.

Feasibility Study on Measuring the Particulate Matter Level in the Atmosphere by Means of Yagi-Uda-Like Antennas.

In this work, the application of a technique for monitoring changes of the dielectric constant of the atmosphere caused by the presence of pollution is discussed. The method is based on changes in the reflection coefficient of the device induced by these dielectric constant variations of the surrounding medium. To that end, several Yagi–Uda-like antenna designs with different size limitations were simulated by using a Method-of-Moments software and optimized by means of a simulated annealing strategy. It has been found that the larger the optimal elements of the array are allowed to be, the higher the sensitivity reached. Thus, in a trade-off between sensitivity and moderate length (regarding flexibility purposes), the most promising solution has been built. This prototype has been experimentally tested in presence of an artificial aerosol made of PAO (polyalphaolefin) oil and black carbon inclusions of a size of 0.2 μm. As a result, potentials for developing a measurement procedure by means of changes in the characteristic parameters of the antenna led by different concentration levels of suspended particles in the surrounding medium are shown. In this manner, a local mapping of polluted levels could be developed in an easy, real-time, and flexible procedure.

An experimental and numerical study of the light scattering properties of ice crystals with black carbon inclusions

We investigate the optical properties of ice crystals nucleated on atmospheric black carbon (BC). The parameters examined in this study are the shape of the ice crystal, the volume fraction of the BC inclusion, and its location inside the crystal. We report on new spectrometer measurements of forward scattering and backward polarization from ice crystals nucleated on BC particles and grown under laboratory-controlled conditions. Data from the Cloud and Aerosol Spectrometer with Polarization (CASPOL) are used for direct comparison with single-particle calculations of the scattering phase matrix. Geometrical optics and discrete dipole approximation techniques are jointly used to provide the best compromise of flexibility and accuracy over a broad range of size parameters. Together with the interpretation of the trends revealed by the CASPOL measurements, the numerical results confirm previous reports on absorption cross-section magnification in the visible light range. Even taking into account effects of crystal shape and inclusion position, the ratio between absorption cross-section of the compound particle and the absorption cross-section of the BC inclusion alone (the absorption magnification) has a lower bound of 1.5; this value increases to 1.7 if the inclusion is centered with respect to the crystal. The simple model of BC-ice particle presented here also offers new insights on the effect of the relative position of the BC inclusion with respect to the crystal's outer surfaces, the shape of the crystal, and its size.

Evaluation of black carbon semi‒direct radiative effect in a climate model

AbstractThe semi‒direct effect of black carbon (BC) is studied by using a newly proposed optical property parameterization for cloud droplets with BC inclusions. Based on Atmospheric Model Intercomparison Project‒type climate model simulations, it is found that the cloud amount can be either enhanced or reduced when BC is included in clouds. The decrease of the global annual mean total cloud amount is only about 0.023%. The 3‒D cloud fraction distribution, however, shows larger changes which vary with latitude. A correlation between the changes of the cloud fraction and the vertical velocity is found. The cloud water path is mainly affected by low clouds and so the impact of BC on the cloud water path is particularly strong. It is shown that the BC above clouds tends to stabilize the atmosphere and enhance the cloud amount in the boundary layer. This can be used to explain the relationship between aerosol optical depth and cloud amount according to satellite data. For BC in clouds and above, the global annual mean enhancement of solar absorption is about 0.049 W m−2 and 0.57 W m−2, respectively. The BC semi‒direct radiative forcing is estimated by subtracting the BC direct forcing from the BC total radiative forcing. The global annual mean of BC direct forcing and semi‒direct forcing at the top of the atmosphere are 0.264 W m−2 and 0.213 W m−2, respectively.

Improved estimates and understanding of global albedo and atmospheric solar absorption

This study integrates available surface‐based and satellite observations of solar radiation at the surface and the top of the atmosphere (TOA) with a comprehensive set of satellite observations of atmospheric and surface optical properties and a Monte Carlo Aerosol‐Cloud‐Radiation (MACR) model to estimate the three fundamental components of the planetary solar radiation budget: Albedo at the TOA; atmospheric solar absorption; and surface solar absorption. The MACR incorporates most if not all of our current understanding of the theory of solar radiation physics including modern spectroscopic water vapor data, minor trace gases, absorbing aerosols including its effects inside cloud drops, 3‐D cloud scattering effects. The model is subject to a severe test by comparing the simulated solar radiation budget with data from 34 globally distributed state‐of‐the art BSRN (Baseline Surface Radiation Network) land stations which began data collection in the mid 1990s. The TOA over these sites were obtained from the CERES (Cloud and Earth's Radiant Energy System) satellites. The simulated radiation budget was within 2 Wm−2for all three components over the BSRN sites. On the other hand, over these same sites, the IPCC‐2007 simulation of atmospheric absorption is smaller by 7–8 Wm−2. MACR was then used with a comprehensive set of model input from satellites to simulate global solar radiation budget. The simulated planetary albedo of 29.0% confirms the value (28.6%) observed by CERES. We estimate the atmospheric absorption to be 82 ± 8 Wm−2 to be compared with the 67 Wm−2 by IPCC models as of 2001 and updated to 76 Wm−2by IPCC‐2007. The primary reasons for the 6 Wm−2 larger solar absorption in our estimates are: updated water vapor spectroscopic database (∼1 Wm−2), inclusion of minor gases (∼0.5 Wm−2), black and brown carbon aerosols (∼4 Wm−2), the inclusion of black carbon in clouds (∼1 Wm−2) and 3‐D effect of clouds (∼1 Wm−2). The fundamental deduction from our study is the remarkable consistency between satellite measurements of the radiation budget and the parameters (aerosols, clouds and surface reflectivity) which determine the radiation budget. Because of this consistency we can account for and explain the global solar radiation budget of the planet within few Wm−2.

Investigating cloud absorption effects: Global absorption properties of black carbon, tar balls, and soil dust in clouds and aerosols

This study examines modeled properties of black carbon (BC), tar ball (TB), and soil dust (SD) absorption within clouds and aerosols to understand better Cloud Absorption Effects I and II, which are defined as the effects on cloud heating of absorbing inclusions in hydrometeor particles and of absorbing aerosol particles interstitially between hydrometeor particles at their actual relative humidity (RH), respectively. The globally and annually averaged modeled 550 nm aerosol mass absorption coefficient (AMAC) of externally mixed BC was 6.72 (6.3–7.3) m2/g, within the laboratory range (6.3–8.7 m2/g). The global AMAC of internally mixed (IM) BC was 16.2 (13.9–18.2) m2/g, less than the measured maximum at 100% RH (23 m2/g). The resulting AMAC amplification factor due to internal mixing was 2.41 (2–2.9), with highest values in high RH regions. The global 650 nm hydrometeor mass absorption coefficient (HMAC) due to BC inclusions was 17.7 (10.6–19) m2/g, ∼9.3% higher than that of the IM‐AMAC. The 650 nm HMACs of TBs and SD were half and 1/190th, respectively, that of BC. Modeled aerosol absorption optical depths were consistent with data. In column tests, BC inclusions in low and mid clouds (CAE I) gave column‐integrated BC heating rates ∼200% and 235%, respectively, those of interstitial BC at the actual cloud RH (CAE II), which itself gave heating rates ∼120% and ∼130%, respectively, those of interstitial BC at the clear‐sky RH. Globally, cloud optical depth increased then decreased with increasing aerosol optical depth, consistent with boomerang curves from satellite studies. Thus, CAEs, which are largely ignored, heat clouds significantly.

Parameterization of cloud optical properties for semidirect radiative forcing

[1] A parameterization of liquid cloud optical properties with a mixture of black carbon is proposed. It is found that the changes in cloud optical properties due to mixture of black carbon can be treated as a perturbation to existing cloud optical property parameterizations in climate models. The advantage of the proposed scheme is that current cloud optical property parameterizations used in climate models can be kept. It is shown that the dominant factor with respect to radiative forcing due to the inclusion of black carbon in cloud droplets is the resulting change in single-scattering albedo values. Therefore, a simple scheme to modify only the single-scattering albedo is considered. The additional consideration of the modification of asymmetry factor only applies to the case of very large black carbon volume fraction. The results in a one-dimensional radiation model show that internal mixtures of black carbon can have a significant impact on solar flux and heating rates. For a black carbon volume fraction of 10−7, the reduction in solar flux at the top of the atmosphere can be over 0.5 Wm−2 and the heating rate can increase by about 0.08 Kd−1 for a solar zenith angle of 53°.

Australian climate–carbon cycle feedback reduced by soil black carbon

Global warming is likely to increase soil organic carbon decomposition, and thus CO2 release to the atmosphere, creating a positive feedback cycle. Inclusion of realistic estimates of soil black carbon in a climate model results in a decrease in soil CO2 emission in Australia by up to 24.4% following a 3 ∘C warming over 100 years, suggesting that black carbon reduces the strength of this feedback. Annual emissions of carbon dioxide from soil organic carbon are an order of magnitude greater than all anthropogenic carbon dioxide emissions taken together1. Global warming is likely to increase the decomposition of soil organic carbon, and thus the release of carbon dioxide from soils2,3,4,5, creating a positive feedback6,7,8,9. Current models of global climate change that recognize this soil carbon feedback are inaccurate if a larger fraction of soil organic carbon than postulated has a very slow decomposition rate. Here we show that by including realistic stocks of black carbon in prediction models, carbon dioxide emissions are reduced by 18.3 and 24.4% in two Australian savannah regions in response to a warming of 3 ∘C over 100 years1. This reduction in temperature sensitivity, and thus the magnitude of the positive feedback, results from the long mean residence time of black carbon, which we estimate to be approximately 1,300 and 2,600 years, respectively. The inclusion of black carbon in climate models is likely to require spatially explicit information about its distribution, given that the black carbon content of soils ranged from 0 to 82% of soil organic carbon in a continental-scale analysis of Australia. We conclude that accurate information about the distribution of black carbon in soils is important for projections of future climate change.

Modeling the Importance of Biota and Black Carbon As Vectors of Polybrominated Diphenyl Ethers (PBDEs) in the Baltic Sea Ecosystem

The POPCYCLING-Baltic model, a nonsteady state spatially resolved mass balance model of chemical transport in the Baltic Sea environment was modified to include black carbon (BC), dissolved organic carbon (DOC) and food-web bioaccumulation. The importance of these modifications to the transport of PBDE congeners BDE-47, -99, -153, and -209 was assessed by comparing time-series simulated with and without black carbon and biota between 1970 and 2005. Inclusion of black carbon improved the model fit to measurements from air, soil, and biota, and had a major effect on the mass balance. Modeled bulk concentrations of PBDEs in sediments and soils increased by a factor of 3 while concentrations in biota decreased by a factor of 2-5. Black carbon also doubled the recovery time of the system due to the limited availability of PBDEs for degradation. In comparison, the inclusion of biota had only a minor effect on the overall mass balance and recovery times. The modified model is constructed as a flexible matrix and can also be applied to persistent organic pollutants in other ecosystems besides the Baltic Sea.

Aerosol absorption and radiative forcing

Abstract. We present a comprehensive examination of aerosol absorption with a focus on evaluating the sensitivity of the global distribution of aerosol absorption to key uncertainties in the process representation. For this purpose we extended the comprehensive aerosol-climate model ECHAM5-HAM by effective medium approximations for the calculation of aerosol effective refractive indices, updated black carbon refractive indices, new cloud radiative properties considering the effect of aerosol inclusions, as well as by modules for the calculation of long-wave aerosol radiative properties and instantaneous aerosol forcing. The evaluation of the simulated aerosol absorption optical depth with the AERONET sun-photometer network shows a good agreement in the large scale global patterns. On a regional basis it becomes evident that the update of the BC refractive indices to Bond and Bergstrom (2006) significantly improves the previous underestimation of the aerosol absorption optical depth. In the global annual-mean, absorption acts to reduce the short-wave anthropogenic aerosol top-of-atmosphere (TOA) radiative forcing clear-sky from −0.79 to −0.53 W m−2 (33%) and all-sky from −0.47 to −0.13 W m−2 (72%). Our results confirm that basic assumptions about the BC refractive index play a key role for aerosol absorption and radiative forcing. The effect of the usage of more accurate effective medium approximations is comparably small. We demonstrate that the diversity in the AeroCom land-surface albedo fields contributes to the uncertainty in the simulated anthropogenic aerosol radiative forcings: the usage of an upper versus lower bound of the AeroCom land albedos introduces a global annual-mean TOA forcing range of 0.19 W m−2 (36%) clear-sky and of 0.12 W m−2 (92%) all-sky. The consideration of black carbon inclusions on cloud radiative properties results in a small global annual-mean all-sky absorption of 0.05 W m−2 and a positive TOA forcing perturbation of 0.02 W m−2. The long-wave aerosol radiative effects are small for anthropogenic aerosols but become of relevance for the larger natural dust and sea-salt aerosols.

Climatic effects of different aerosol types in China simulated by the UCLA general circulation model

The climatic effects of various types of aerosol in China have been investigated by using the atmospheric general circulation model (AGCM) developed at the University of California, Los Angeles (UCLA). The model includes an efficient and physically based radiation parameterization scheme specifically developed for application to clouds and aerosols. Simulation results show that inclusion of a background aerosol optical depth of 0.2 reduces the global mean net surface solar flux by about 5 W m−2 and produces a decrease in precipitation in the tropics as a result of decreased temperature contrast between this area and the middle to high latitudes, which suppresses tropical convection. These decreases have partially corrected the overestimates in the surface solar flux and precipitation in the UCLA AGCM simulations without the aerosol effect. The experiment with increased aerosol optical depths in China shows a noticeable increase in precipitation in the southern part of China in July due to the cooling in the midlatitudes that leads to the strengthening of the Hadley circulation. Aerosol types play an important role in the determination of the global mean radiation budget and regional climate. While sulfates mainly reflect solar radiation and induce negative forcing at the surface, black carbon and large dust particles absorb substantial solar radiation and have a positive solar forcing at the top of the atmosphere, but reduce the solar radiation reaching the surface. Large dust particles also have a significant effect on thermal IR radiation under clear conditions, but this effect is largely masked by clouds generated from the model in AGCM simulations. Black carbon and large dust particles in China would heat the air column in the middle to high latitudes and tend to move the simulated precipitation inland, i.e., toward the Himalayas. The inclusion of black carbon in our simulations has not produced the “north drought/south flooding” precipitation pattern that has frequently occurred in China during the past 50 years.

Effects of Externally-Through-Internally-Mixed Soot Inclusions within Clouds and Precipitation on Global Climate

This paper examines the incremental global climate response of black carbon (BC), the main component of soot, due to absorption and scattering by BC inclusions within cloud and precipitation particles. Modeled soot is emitted as an externally mixed aerosol particle. It evolves to an internal mixture through condensation, hydration, dissolution, dissociation, crystallization, aqueous chemistry, coagulation, and cloud processing. Size-resolved cloud liquid and ice particles grow by condensation onto size-resolved soot and other particles. Cloud particles grow to precipitation by coagulation and the Bergeron process. Cloud and precipitation particles also undergo freezing, melting, evaporation, sublimation, and coagulation with interstitial aerosol particles. Soot, which is tracked in cloud and precipitation particles of all sizes, is removed by rainout, washout, sedimentation, and dry deposition. Two methods of treating the optics of BC in size-resolved cloud liquid, ice and graupel are compared: the core-shell approximation (CSA) and the iterative dynamic effective medium approximation (DEMA). The 10-year global near-surface incremental temperature response due to fossil fuel (ff), biofuel (bf), and biomass burning (bb) BC within clouds with the DEMA was slightly stronger than that with the CSA, but both enhancements were <+0.05 K. The ff+bf portion may be approximately 60% of the total, suggesting that BC inclusions within clouds may enhance the near-surface temperature response of ff+bf soot due to all processes (estimated as approximately 0.27 K), by <10%, strengthening the possible climate impact of BC. BC cloud absorption was also found to increase water vapor, decrease precipitation, and decrease cloud fraction. The increase in water vapor at the expense of precipitation contributed to warming in addition to that of the cloud BC absorption itself. Aerosol-hydrometeor coagulation followed by hydrometeor evaporation may have caused almost twice the BC internal mixing as aerosol-aerosol coagulation.

Sensitivity of global‐scale climate change attribution results to inclusion of fossil fuel black carbon aerosol

It is likely that greenhouse gas emissions caused most of the global mean warming observed during the 20th century, and that sulphate aerosols counteracted this warming to some extent, by reflecting solar radiation to space and thereby cooling the planet. However, the importance of another aerosol, namely black carbon, could be underestimated. Here we include fossil fuel black carbon aerosol in a detection and attribution analysis with greenhouse gas and sulphate aerosols. We find that most of the warming of the 20th Century is attributable to changes in greenhouse gases offset by net aerosol cooling. However the pattern of temperature change due to black carbon is currently indistinguishable from the sulphate aerosol pattern of temperature change. The attribution of temperature change due to greenhouse gases is not sensitive to the inclusion of black carbon. We can be confident about the overall attribution of total aerosols, but less so about the contributions of black carbon emissions to 20th century climate change. This work presents no evidence that black carbon aerosol forcing outweighed the cooling due to sulphate aerosol.

The effect of black carbon on scattering and absorption of solar radiation by cloud droplets

Scattering and absorption characteristics of water cloud droplets containing black carbon (BC) inclusions are calculated at a visible wavelength of 0.55 μm by a combination of ray-tracing and Monte Carlo techniques. In addition, Lorenz–Mie calculations are performed assuming that the same amount of BC particles are mixed with water droplets externally. The results show that it is unlikely under normal conditions that BC aerosols can modify scattering and absorption properties of cloud droplets in any significant way except for geographical locations very close to major sources of BC. The differences in the single-scattering co-albedo and asymmetry parameter between BC-fraction-equivalent internal and external mixtures are negligibly small for normal black carbon loadings, which makes possible the use of the much simpler external mixing model in radiative transfer modeling irrespective of the actual form of mixing. For a fixed amount of BC internally mixed with cloud droplets, the absorption is maximal when the effective radius of the BC inclusions is about 0.05– 0.06 μm .

Response Characteristics of the Particle Measuring Systems Active Scattering Aerosol Spectrometer Probes

Predictions of the size response of various light-scattering aerosol counters manufactured by Particle Measuring Systems are reported. Models that exploit the high intensity of light available within the cavity of a He-Ne gas laser (generically referred to by the manufacturer as ''active scattering aerosol spectrometer probes'') are considered. The new response function properly averages over particle trajectories through nodes, antinodes, and intermediate regions of the intracavity laser beam. Our studies address probes having two basic scattering geometries: those that collect light scattered over a relatively narrow solid angle (subtending angles between 4° and 22° from the laser beam axis, as in the model ASASP-300 and ASASP-300X probes) and those that collect light over a rather large solid angle (between 35° and 120° , as in the ASASP-X, ASASP-100X, LAS-250X, LAS-X, and HS-LAS probes). The theoretical response predictions for both narrow-angle and wide-angle probes are compared to previous measurements of monodisperse test aerosols of polystyrene latex, dyoctylphthalate, nigrosin dye, and carbon black. The new response function predicts smoother dependence on particle size than the previous response function of Pinnick and Auvermann (1979) and is in better agreement with measurement. Response calculations for common atmospheric aerosol (water, sulfuric acid, ammonium sulfate, and black carbon) reveal the considerable sensitivity of the response to particle dielectric properties. Response functions for internal mixtures (black carbon inclusions in water droplets, quartz in sulfuric acid, carbon in ammonium sulfate, and metal in sulfuric acid) are somewhat different than those for homogeneous particles. Comparison of response calculations with the manufacturer's calibration reveal conditions for which the manufacturer's calibration is most appropriate and the potential for errors (as much as a factor of two in sizing) when it is blindly applied. Finally, response functions for multiline laser operation, as the manufacturer suggests might be appropriate for the HS-LAS and LAS-X probes, are nearly the same as for single-line lasing. These results should help the user of these instruments to more realistically interpret size distribution measurements.