scholarly journals Influence of light-absorbing particles on snow spectral irradiance profiles

2019 ◽  
Vol 13 (8) ◽  
pp. 2169-2187 ◽  
Author(s):  
Francois Tuzet ◽  
Marie Dumont ◽  
Laurent Arnaud ◽  
Didier Voisin ◽  
Maxim Lamare ◽  
...  
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Black Carbon ◽  
Mineral Dust ◽  
Surface Energy Budget ◽  
Spectral Irradiance ◽  
Light Extinction ◽  
Attractive Alternative ◽  
Chemical Measurements ◽  
Radiative Impact

Abstract. Light-absorbing particles (LAPs) such as black carbon or mineral dust are some of the main drivers of snow radiative transfer. Small amounts of LAPs significantly increase snowpack absorption in the visible wavelengths where ice absorption is particularly weak, impacting the surface energy budget of snow-covered areas. However, linking measurements of LAP concentration in snow to their actual radiative impact is a challenging issue which is not fully resolved. In the present paper, we point out a new method based on spectral irradiance profile (SIP) measurements which makes it possible to identify the radiative impact of LAPs on visible light extinction in homogeneous layers of the snowpack. From this impact on light extinction it is possible to infer LAP concentrations present in each layer using radiative transfer theory. This study relies on a unique dataset composed of 26 spectral irradiance profile measurements in the wavelength range 350–950 nm with concomitant profile measurements of snow physical properties and LAP concentrations, collected in the Alps over two snow seasons in winter and spring conditions. For 55 homogeneous snow layers identified in our dataset, the concentrations retrieved from SIP measurements are compared to chemical measurements of LAP concentrations. A good correlation is observed for measured concentrations higher than 5 ng g−1 (r2=0.81) despite a clear positive bias. The potential causes of this bias are discussed, underlining a strong sensitivity of our method to LAP optical properties and to the relationship between snow microstructure and snow optical properties used in the theory. Additional uncertainties such as artefacts in the measurement technique for SIP and chemical contents along with LAP absorption efficiency may explain part of this bias. In addition, spectral information on LAP absorption can be retrieved from SIP measurements. We show that for layers containing a unique absorber, this absorber can be identified in some cases (e.g. mineral dust vs. black carbon). We also observe an enhancement of light absorption between 350 and 650 nm in the presence of liquid water in the snowpack, which is discussed but not fully elucidated. A single SIP acquisition lasts approximately 1 min and is hence much faster than collecting a profile of chemical measurements. With the recent advances in modelling LAP–snow interactions, our method could become an attractive alternative to estimate vertical profiles of LAP concentrations in snow.

scholarly journals Influence of light absorbing particles on snow spectral irradiance profiles

2019 ◽  
Author(s):  
François Tuzet ◽  
Marie Dumont ◽  
Laurent Arnaud ◽  
Didier Voisin ◽  
Maxim Lamare ◽  
...  
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Black Carbon ◽  
Mineral Dust ◽  
Strong Dependence ◽  
Surface Energy Budget ◽  
Spectral Irradiance ◽  
Light Extinction ◽  
Chemical Measurements ◽  
Radiative Impact

Abstract. Light Absorbing Particles (LAP) such as black carbon or mineral dust are some of the main drivers of snow radiative transfer. Small amounts of LAP significantly increase snowpack absorption in the visible wavelengths where ice absorption is particularly weak, impacting the surface energy budget of snow-covered areas. However, linking measurements of LAP concentration in snow to their actual radiative impact is a challenging issue which is not fully resolved. In the present paper, we point out a new method based on Spectral Irradiance Profile (SIP) measurements which makes it possible to identify the radiative impact of LAP on visible light extinction in homogeneous layers of the snowpack. From this impact on light extinction it is possible to infer LAP concentrations present in each layer using radiative transfer theory. This study relies on a unique dataset composed of 26 spectral irradiance profile measurements in the wavelength range 350–950 nm with concomitant profile measurements of snow physical properties and LAP concentrations, collected in the Alps over two snow seasons in winter and spring conditions. For 55 homogeneous snow layers identified in our dataset, the concentrations retrieved from SIP measurements are compared to chemical measurements of LAP concentrations. A good correlation is observed for measured concentrations higher than 5 ng g−1 (r2 = 0.74) despite a clear positive bias. The potential causes of this bias are discussed, underlining a strong dependence of our method to LAP optical properties and to the relationship between snow microstructure and snow optical properties used in the theory. Additional uncertainties such as artefacts in the measurement technique for SIP and chemical contents along with LAP absorption efficiency, may explain part of this bias. In addition, spectral information on LAP absorption can be retrieved from SIP measurements. We show that for layers containing a unique absorber, this absorber can be identified in some cases (e.g: mineral dust vs black carbon). We also observe an enhancement of light absorption between 350 and 650 nm in presence of liquid water in the snowpack which is discussed but not fully elucidated. A single SIP acquisition lasts approximately one minute and is hence much faster than collecting a profile of chemical measurements. With the recent advances in modelling LAP-snow interactions, our method could become an attractive alternative to estimate vertical profiles of LAP concentrations in snow.

scholarly journals Sensitivity of aerosol radiative effects to different mixing assumptions in the AEROPT 1.0 submodel of the EMAC atmospheric-chemistry–climate model

2014 ◽  
Vol 7 (5) ◽  
pp. 2503-2516 ◽  
Author(s):  
K. Klingmüller ◽  
B. Steil ◽  
C. Brühl ◽  
H. Tost ◽  
J. Lelieveld
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Black Carbon ◽  
Atmospheric Chemistry ◽  
Radiative Forcing ◽  
Climate Model ◽  
Mixing Rule ◽  
Aerosol Optical Properties ◽  
Internal Mixing ◽  
Aerosol Radiative

Abstract. The modelling of aerosol radiative forcing is a major cause of uncertainty in the assessment of global and regional atmospheric energy budgets and climate change. One reason is the strong dependence of the aerosol optical properties on the mixing state of aerosol components, such as absorbing black carbon and, predominantly scattering sulfates. Using a new column version of the aerosol optical properties and radiative-transfer code of the ECHAM/MESSy atmospheric-chemistry–climate model (EMAC), we study the radiative transfer applying various mixing states. The aerosol optics code builds on the AEROPT (AERosol OPTical properties) submodel, which assumes homogeneous internal mixing utilising the volume average refractive index mixing rule. We have extended the submodel to additionally account for external mixing, partial external mixing and multilayered particles. Furthermore, we have implemented the volume average dielectric constant and Maxwell Garnett mixing rule. We performed regional case studies considering columns over China, India and Africa, corroborating much stronger absorption by internal than external mixtures. Well-mixed aerosol is a good approximation for particles with a black-carbon core, whereas particles with black carbon at the surface absorb significantly less. Based on a model simulation for the year 2005, we calculate that the global aerosol direct radiative forcing for homogeneous internal mixing differs from that for external mixing by about 0.5 W m−2.

scholarly journals Modelling the mineralogical composition and solubility of mineral dust in the Mediterranean area with CHIMERE 2017r4

2020 ◽  
Vol 13 (4) ◽  
pp. 2051-2071 ◽  
Author(s):  
Laurent Menut ◽  
Guillaume Siour ◽  
Bertrand Bessagnet ◽  
Florian Couvidat ◽  
Emilie Journet ◽  
...  
Keyword(s):  
Optical Properties ◽  
Transport Model ◽  
Mineral Dust ◽  
Mineralogical Composition ◽  
Mediterranean Area ◽  
Mineral Species ◽  
Chemistry Transport Model ◽  
Deposition Fluxes ◽  
Global Databases ◽  
Radiative Impact

Abstract. Modelling of mineral dust is often done using one single mean species. But for biogeochemical studies, it could be useful to access to a more detailed information on differentiated mineral species and the associated chemical composition. Differentiating between mineral species would also induce different optical properties and densities and then different radiative impact, transport and deposition. In this study, the mineralogical differentiation is implemented in the CHIMERE regional chemistry-transport model, by using global databases. The results show that this implementation does not change the results much in terms of aerosol optical depth, surface concentrations and deposition fluxes. But the information on mineralogy, with a high spatial (a few kilometres) and temporal (1 h) resolution, is now available and is ready to be used for future biogeochemical studies.

scholarly journals Sensitivity of aerosol extinction to new mixing rules in the AEROPT submodel of the ECHAM5/MESSy1.9 atmospheric chemistry (EMAC) model

2014 ◽  
Vol 7 (3) ◽  
pp. 3367-3402
Author(s):  
K. Klingmüller ◽  
B. Steil ◽  
C. Brühl ◽  
H. Tost ◽  
J. Lelieveld
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Black Carbon ◽  
Atmospheric Chemistry ◽  
Radiative Forcing ◽  
Strong Dependence ◽  
Mixing Rule ◽  
Aerosol Optical Properties ◽  
Volume Average ◽  
Internal Mixing

Abstract. The modelling of aerosol radiative forcing is a major cause of uncertainty in the assessment of global and regional atmospheric energy budgets and climate change. One reason is the strong dependence of the aerosol optical properties on the mixing state of aerosol components like black carbon and sulphates. Using a new column version of the aerosol optical properties and radiative transfer code of the atmospheric chemistry-climate model EMAC, we study the radiative transfer applying various mixing states. The aerosol optics code builds on the AEROPT submodel which assumes homogeneous internal mixing utilising the volume average refractive index mixing rule. We have extended the submodel to additionally account for external mixing, partial external mixing and multi-layered particles. Furthermore, we have implemented the volume average dielectric-constant and Maxwell Garnett Mixing rule. We performed regional case studies considering columns over China, India and Africa, corroborating much stronger absorption by internal than external mixtures. Well mixed aerosol is a good approximation for particles with a black carbon core, whereas particles with black carbon at the surface absorb significantly less. Based on a model simulation for the year 2005 we calculate that the global aerosol direct radiative-forcing for homogeneous internal mixing differs from that for external mixing by about 0.5 W m−2.

scholarly journals Black carbon fractal morphology and short-wave radiative impact: a modelling study

2011 ◽  
Vol 11 (8) ◽  
pp. 23103-23137
Author(s):  
M. Kahnert ◽  
A. Devasthale
Keyword(s):  
Optical Properties ◽  
Fractal Dimension ◽  
Black Carbon ◽  
Radiative Forcing ◽  
Homogeneous Sphere ◽  
Radiative Impacts ◽  
Radiative Impact ◽  
Sphere Approximation ◽  
Carbon Aerosols ◽  
Black Carbon Aerosols

Abstract. We investigate the impact of the morphological properties of freshly emitted black carbon aerosols on optical properties and on radiative forcing. To this end, we model the optical properties of fractal black carbon aggregates by use of numerically exact solutions to Maxwell's equations within a spectral range from the UVC to the mid-IR. The results are coupled to radiative transfer computations, in which we consider six realistic case studies representing different atmospheric pollution conditions and surface albedos. The spectrally integrated radiative impacts of black carbon are compared for two different fractal morphologies, which brace the range of recently reported experimental observations of black carbon fractal structures. We also gauge our results by performing corresponding calculations based on the homogeneous sphere approximation, which is commonly employed in climate models. We find that at top of atmosphere the aggregate models yield radiative impacts that can be as much as 2 times higher than those based on the homogeneous sphere approximation. An aggregate model with a low fractal dimension can predict a radiative impact that is higher than that obtained with a high fractal dimension by a factor ranging between 1.1–1.6. Although the lower end of this scale seems like a rather small effect, a closer analysis reveals that the single scattering optical properties of more compact and more lacy aggregates differ considerably. In radiative flux computations there can be a partial cancellation due to the opposing effects of differences in the optical cross sections and asymmetry parameters. However, this cancellation effect can strongly depend on atmospheric conditions and is therefore quite unpredictable. We conclude that the fractal morphology of black carbon aerosols and their fractal parameters can have a profound impact on their radiative forcing effect, and that the use of the homogeneous sphere model introduces unacceptably high biases in radiative impact studies. We emphasise that there are other potentially important morphological features that have not been addressed in the present study, such as sintering and coating of freshly emitted black carbon by films of organic material.

scholarly journals Impact of mineral dust on shortwave and longwave radiation: evaluation of different vertically-resolved parameterizations in 1-D radiative transfer computations

2018 ◽  
Author(s):  
Maria José Granados-Muñoz ◽  
Michael Sicard ◽  
Roberto Román ◽  
Jose Antonio Benavent-Oltra ◽  
Rubén Barragán ◽  
...  
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Mineral Dust ◽  
Radiative Properties ◽  
Radiative Fluxes ◽  
Microphysical Properties ◽  
Aerosol Radiative

Abstract. Aerosol radiative properties are investigated in South-eastern Spain during a dust event on June 16–17, 2013 in the framework of the ChArMEx/ADRIMED (Chemistry-Aerosol Mediterranean Experiment/Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region) campaign. Particle optical and microphysical properties from ground-based sun/sky photometer and lidar measurements, as well as in situ measurements onboard the SAFIRE ATR 42 French research aircraft are used to create a set of different levels of input parameterizations which feed the 1-D radiative transfer model (RTM) GAME (Global Atmospheric ModEl). We consider three datasets: 1) a first parametrization based on the retrievals by an advanced aerosol inversion code (GRASP; Generalized Retrieval of Aerosol and Surface Properties) applied to combined photometer and lidar data; 2) a parameterization based on the photometer columnar optical properties and vertically-resolved lidar retrievals with the two-component Klett-Fernald algorithm; and 3) a parametrization based on vertically-resolved optical and microphysical aerosol properties measured in situ by the aircraft instrumentation. Once retrieved, the outputs of the RTM in terms of both shortwave and longwave radiative fluxes are contrasted against ground-, satellite- and in situ airborne measurements. In addition, the outputs of the model in terms of the aerosol direct radiative effect are discussed with respect to the different input parameterizations. Results show that calculated atmospheric radiative fluxes differ no more than 7 % to the measured ones. The three parametrization datasets produce aerosol radiative effects with differences up to 10 W m−2 in the shortwave spectral range (mostly due to differences in the aerosol optical depth), and 2 W m−2 for the longwave (mainly due to differences in the aerosol optical depth but also to the coarse mode radius used to calculate the radiative properties). The study reveals the complexity of parameterizing 1-D RTMs as sizing and characterising the optical properties of mineral dust is challenging. The use of advanced remote sensing data and processing, in combination with closure studies on the optical/microphysical properties from in situ aircraft measurements when available, is recommended.

scholarly journals Perturbations of the optical properties of mineral dust particles by mixing with black carbon: a numerical simulation study

2015 ◽  
Vol 15 (12) ◽  
pp. 6913-6928 ◽  
Author(s):  
B. V. Scarnato ◽  
S. China ◽  
K. Nielsen ◽  
C. Mazzoleni
Keyword(s):  
Optical Properties ◽  
Black Carbon ◽  
Dust Particle ◽  
Mineral Dust ◽  
Complex Mixture ◽  
Ambient Air ◽  
Dust Particles ◽  
Field Observations ◽  
Chemical Transformations ◽  
Large Variability

Abstract. Field observations show that individual aerosol particles are a complex mixture of a wide variety of species, reflecting different sources and physico-chemical transformations. The impacts of individual aerosol morphology and mixing characteristics on the Earth system are not yet fully understood. Here we present a sensitivity study on climate-relevant aerosols optical properties to various approximations. Based on aerosol samples collected in various geographical locations, we have observationally constrained size, morphology and mixing, and accordingly simulated, using the discrete dipole approximation model (DDSCAT), optical properties of three aerosols types: (1) bare black carbon (BC) aggregates, (2) bare mineral dust, and (3) an internal mixture of a BC aggregate laying on top of a mineral dust particle, also referred to as polluted dust. DDSCAT predicts optical properties and their spectral dependence consistently with observations for all the studied cases. Predicted values of mass absorption, scattering and extinction coefficients (MAC, MSC, MEC) for bare BC show a weak dependence on the BC aggregate size, while the asymmetry parameter (g) shows the opposite behavior. The simulated optical properties of bare mineral dust present a large variability depending on the modeled dust shape, confirming the limited range of applicability of spheroids over different types and size of mineral dust aerosols, in agreement with previous modeling studies. The polluted dust cases show a strong decrease in MAC values with the increase in dust particle size (for the same BC size) and an increase of the single scattering albedo (SSA). Furthermore, particles with a radius between 180 and 300 nm are characterized by a decrease in SSA values compared to bare dust, in agreement with field observations. This paper demonstrates that observationally constrained DDSCAT simulations allow one to better understand the variability of the measured aerosol optical properties in ambient air and to define benchmark biases due to different approximations in aerosol parametrization.

scholarly journals Composition, size distribution, optical properties and radiative effects of re-suspended local mineral dust of Rome area by individual-particle microanalysis and radiative transfer modelling

2015 ◽  
Vol 15 (9) ◽  
pp. 13347-13393
Author(s):  
A. Pietrodangelo ◽  
R. Salzano ◽  
C. Bassani ◽  
S. Pareti ◽  
C. Perrino
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Size Distribution ◽  
Solar Irradiance ◽  
Mineral Dust ◽  
Road Dust ◽  
Individual Particle ◽  
Mineral Species ◽  
X Ray ◽  
Transfer Modelling

Abstract. New information on the PM10 mineral dust from site-specific (Rome area, Latium) outcropped rocks, and on the microphysics, optical properties and radiative effects of mineral dust at local level were gained in this work. A multi-disciplinary approach was used, based on individual-particle scanning electron microscopy with X-ray energy-dispersive microanalysis (SEM XEDS), X-ray diffraction (XRD) analysis of dust, size distribution of mineral particles, and radiative transfer modelling (RTM).The mineral composition of Rome lithogenic PM10 varies between an end-member dominated by silicate minerals and one exclusively composed of calcite. The first is obtained from volcanic lithotypes, the second from travertine or limestones; lithogenic PM10 with intermediate composition derives mainly from siliciclastic rocks or marlstones of Rome area. Size and mineral species of PM10 particles of silicate-dominated dust types are tuned mainly by weathering and, to lesser extent, by debris formation or crystallization; chemical precipitation of CaCO3 plays a major role in calcite-dominated types. These differences are evidenced by the diversity of volume distributions, within either dust types, or mineral species. Further differences are observed between volume distributions of calcite from travertine (natural source) and from road dust (anthropic source), specifically on the width, shape and enrichment of the fine fraction (unimodal at 5 μm a.d. for travertine, bimodal at 3.8 and 1.8 μm a.d. for road dust). Log-normal probability density functions of volcanics and travertine dusts affect differently the single scattering albedo (SSA) and the asymmetry parameter (g) in the VISible and Near Infrared (NIR) regions, depending also on the absorbing/non-absorbing character of volcanics and travertine, respectively. The downward component of the BOA solar irradiance simulated by RTM for a volcanics-rich or travertine-rich atmosphere shows that volcanics contribution to the solar irradiance differs significantly from that of travertine in the NIR region, while similar contributions are modelled in the VIS.

scholarly journals Optical properties of laboratory grown sea ice doped with light absorbing impurities (black carbon)

2017 ◽  
Author(s):  
Amelia A. Marks ◽  
Maxim L. Lamare ◽  
Martin D. King
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Sea Ice ◽  
Black Carbon ◽  
Penetration Depth ◽  
Cross Sections ◽  
Absorption Cross ◽  
Light Penetration ◽  
Irradiance Data ◽  
Snow Model

Abstract. Sea ice radiative-transfer models are of great importance for prediction of future sea ice trends but they are limited by uncertainty in models and requirement for evaluation of modelled irradiance data against measured irradiance data. Presented here are the first results from the Royal Holloway sea ice simulator used to evaluate the output of the TUV-snow radiative-transfer model against the optical properties from the simulated sea ice. The sea ice simulator creates a realistic sea ice environment where both optical (reflectance and light penetration depth (e-folding depth)) and physical (temperature, salinity, density) properties of a ∼ 30 cm thick sea ice can be monitored and measured. Using albedo and e-folding depth data measured from simulated sea ice, scattering and absorption cross-sections of the ice are derived using the TUV-snow model. Absorption cross-sections for the ice are highly wavelength dependent, suggesting the addition of a further absorbing impurity in the ice matching the absorption spectrum of algae. Scattering cross-sections were wavelength independent with values ranging from 0.012 and 0.032 cm2 kg−1 for different ice created in the simulator. Reflectance and light penetration depth (e-folding depth) of sea ice is calculated from the derived values of the scattering and absorption cross-section using the TUV-snow model within error of the experiment. The model is also shown to replicate ice optical properties for sea ice with an extra layer doped with black carbon, well within error of the experiment. Particulate black carbon at mass ratios of 75, 150 and 300 ng g−1 in a 5 cm ice layer lowers the albedo by 97 %, 90 %, and 79 % compared to clean ice at a wavelength of 500 nm.

scholarly journals Impact of mineral dust on shortwave and longwave radiation: evaluation of different vertically resolved parameterizations in 1-D radiative transfer computations

2019 ◽  
Vol 19 (1) ◽  
pp. 523-542 ◽  
Author(s):  
María José Granados-Muñoz ◽  
Michael Sicard ◽  
Roberto Román ◽  
Jose Antonio Benavent-Oltra ◽  
Rubén Barragán ◽  
...  
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Mineral Dust ◽  
Radiative Properties ◽  
Radiative Fluxes ◽  
Microphysical Properties ◽  
Aerosol Radiative

Abstract. Aerosol radiative properties are investigated in southeastern Spain during a dust event on 16–17 June 2013 in the framework of the ChArMEx/ADRIMED (Chemistry-Aerosol Mediterranean Experiment/Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region) campaign. Particle optical and microphysical properties from ground-based sun/sky photometer and lidar measurements, as well as in situ measurements on board the SAFIRE ATR 42 French research aircraft, are used to create a set of different levels of input parameterizations, which feed the 1-D radiative transfer model (RTM) GAME (Global Atmospheric ModEl). We consider three datasets: (1) a first parameterization based on the retrievals by an advanced aerosol inversion code (GRASP; Generalized Retrieval of Aerosol and Surface Properties) applied to combined photometer and lidar data, (2) a parameterization based on the photometer columnar optical properties and vertically resolved lidar retrievals with the two-component Klett–Fernald algorithm, and (3) a parameterization based on vertically resolved optical and microphysical aerosol properties measured in situ by the aircraft instrumentation. Once retrieved, the outputs of the RTM in terms of both shortwave and longwave radiative fluxes are compared against ground and in situ airborne measurements. In addition, the outputs of the model in terms of the aerosol direct radiative effect are discussed with respect to the different input parameterizations. Results show that calculated atmospheric radiative fluxes differ no more than 7 % from the measured ones. The three parameterization datasets produce a cooling effect due to mineral dust both at the surface and the top of the atmosphere. Aerosol radiative effects with differences of up to 10 W m−2 in the shortwave spectral range (mostly due to differences in the aerosol optical depth) and 2 W m−2 for the longwave spectral range (mainly due to differences in the aerosol optical depth but also to the coarse mode radius used to calculate the radiative properties) are obtained when comparing the three parameterizations. The study reveals the complexity of parameterizing 1-D RTMs as sizing and characterizing the optical properties of mineral dust is challenging. The use of advanced remote sensing data and processing, in combination with closure studies on the optical and microphysical properties from in situ aircraft measurements when available, is recommended.

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