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3. Light-absorbing black carbon and brown carbon components of smoke aerosol from DSCOVR EPIC measurements over North America and central Africa.

Author

Choi, Myungje, Lyapustin, Alexei, Schuster, Gregory L., Go, Sujung, Wang, Yujie, Korkin, Sergey, Kahn, Ralph, Reid, Jeffrey S., Hyer, Edward J., Eck, Thomas F., Chin, Mian, Diner, David J., Kalashnikova, Olga, Dubovik, Oleg, Kim, Jhoon, and Moosmüller, Hans

Subjects
INTERTROPICAL convergence zone, AIR quality, RADIATIVE forcing, TROPICAL forests, AEROSOLS, SOOT
Abstract

Wildfires and agricultural burning generate seemingly increasing smoke aerosol emissions, impacting societal and natural ecosystems. To understand smoke's effects on climate and public health, we analyzed the spatiotemporal distribution of smoke aerosols, focusing on two major light-absorbing components, namely black carbon (BC) and brown carbon (BrC) aerosols. Using NASA's Earth Polychromatic Imaging Camera (EPIC) instrument aboard NOAA's Deep Space Climate Observatory (DSCOVR) spacecraft, we inferred BC and BrC volume fractions and particle mass concentrations based on spectral absorption provided by the Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm with 1–2 h temporal resolution and ∼ 10 km spatial resolution over North America and central Africa. Our analyses of regional smoke properties reveal distinct characteristics for aerosol optical depth (AOD) at 443 nm, spectral single-scattering albedo (SSA), aerosol layer height (ALH), and BC and BrC amounts. Smoke aerosols in North America showed extremely high AOD up to 6, with elevated ALH (6–7 km) and significant BrC components up to 250 mg m -2 along the transport paths, whereas the smoke aerosols in central Africa exhibited stronger light absorption (i.e., lower SSA) and lower AOD, resulting in higher-BC mass concentrations and similar BrC mass concentrations than the cases in North America. Seasonal burning source locations in central Africa, following the seasonal shift in the Intertropical Convergence Zone and diurnal variations in smoke amounts, were also captured. A comparison of retrieved AOD 443 , SSA 443 , SSA 680 , and ALH with collocated AERONET and CALIOP measurements shows agreement with RMSE values of 0.2, 0.03–0.04, 0.02–0.04, and 0.8–1.3 km, respectively. An analysis of the spatiotemporal average reveals distinct geographical characteristics in smoke properties closely linked to burning types and meteorological conditions. Forest wildfires over western North America generated smoke with a small-BC volume fraction of 0.011 and a high ALH with large variability (2.2 ± 1.2 km), whereas smoke from wildfires and agricultural burning over Mexico region shows more absorption and low ALH. Smoke from savanna fires over central Africa had the most absorption, with a high-BC volume fraction (0.015) and low ALH with a small variation (1.8 ± 0.6 km) among the analyzed regions. Tropical forest smoke was less absorbing and had a high variance in ALH. We also quantify the estimation uncertainties related to the assumptions of BC and BrC refractive indices. The MAIAC EPIC smoke properties with BC and BrC volume and mass fractions and assessment of the layer height provide observational constraints for radiative forcing modeling and air quality and health studies. [ABSTRACT FROM AUTHOR]

Published
2024
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7. Observationally constrained regional variations of shortwave absorption by iron oxides emphasize the cooling effect of dust

Author

Universitat Politècnica de Catalunya. Departament d'Enginyeria de Projectes i de la Construcció, Obiso, Vincenzo, Gonçalves Ageitos, María, Pérez García-Pando, Carlos, Perlwitz, Jan, Schuster, Gregory L., Bauer, Susanne, di Biagio, C, Formenti, Paola, Tsigaridis, Kostas, Miller, Ron L., Universitat Politècnica de Catalunya. Departament d'Enginyeria de Projectes i de la Construcció, Obiso, Vincenzo, Gonçalves Ageitos, María, Pérez García-Pando, Carlos, Perlwitz, Jan, Schuster, Gregory L., Bauer, Susanne, di Biagio, C, Formenti, Paola, Tsigaridis, Kostas, and Miller, Ron L.

Abstract

The composition of soil dust aerosols derives from the mineral abundances in the parent soils that vary across dust source regions. Nonetheless, Earth system models (ESMs) have traditionally represented mineral dust as a globally homogeneous species. The growing interest in modeling dust mineralogy, facilitated by the recognized sensitivity of the dust climate impacts to composition, has motivated state-of-the-art ESMs to incorporate the mineral speciation of dust along with its effect upon the dust direct radiative effect (DRE). In this work, we enable the NASA Goddard Institute for Space Studies ModelE2.1 to calculate the shortwave (SW) DRE accounting for the regionally varying soil mineralogy. Mineral–radiation interaction at solar wavelengths is calculated according to two alternative coupling schemes: (1) external mixing of three mineral components that are optically distinguished, one of which contains embedded iron oxides; (2) a single internal mixture of all dust minerals with a dynamic fraction of iron oxides that varies regionally and temporally. We link dust absorption to the fractional mass of iron oxides based on recent chamber measurements using natural dust aerosol samples. We show that coupled mineralogy overall enhances the scattering by dust, and thus the global cooling, compared to our control run with globally uniform composition. According to the external mixing scheme, the SW DRE at the top of atmosphere (TOA) changes from -0.25 to -0.30Wm-2, corresponding to a change in the net DRE, including the longwave effect, from -0.08 to -0.12Wm-2. The cooling increase is accentuated when the internal mixing scheme is configured: the SW DRE at the TOA becomes -0.34Wm-2 with a net DRE of -0.15Wm-2. The varying composition modifies the regional distribution of single scattering albedo (SSA), whose variations in specific regions can be remarkable (above 0.03) and significantly modify the regional SW DRE. Evaluation against the AErosol RObotic NETwork (AERON, Vincenzo Obiso was supported by the NASA Postdoctoral Program at the NASA Goddard Institute for Space Studies, administered by Oak Ridge Associated Universities under contract with NASA. Additional support was provided by the NASA Modeling, Analysis and Prediction Program (NNG14HH42I) and the Earth Surface Mineral Dust Source Investigation (EMIT), a NASA Earth Ventures Instrument (EVI-4) mission, both of which also supported Ron L. Miller. Carlos Pérez García-Pando, María Gonçalves Ageitos and Vincenzo Obiso acknowledge funding by the European Research Council under the Horizon 2020 research and innovation program through the ERC Consolidator Grant FRAGMENT (grant agreement no. 773051), the AXA Research Fund through the AXA Chair on Sand and Dust Storms at the Barcelona Supercomputing Center (BSC), the EuropeanUnion’s Horizon2020research andinnovation program under grant agreement no. 821205 (FORCeS) and national grants HEAVY PID2022-140365OB-I00 and BIOTA PID2022 -Vincenzo Obiso was supported by the NASA Postdoctoral Program at the NASA Goddard Institute for Space Studies, administered by Oak Ridge Associated Universities under contract with NASA. Additional support was provided by the NASA Modeling, Analysis and Prediction Program (NNG14HH42I) and the Earth Surface Mineral Dust Source Investigation (EMIT), a NASA Earth Ventures Instrument (EVI-4) mission, both of which also supported Ron L. Miller. Carlos Pérez García-Pando, María Gonçalves Ageitos and Vincenzo Obiso acknowledge funding by the European Research Council under the Horizon 2020 research and innovation program through the ERC Consolidator Grant FRAGMENT (grant agreement no. 773051), the AXA Research Fund through the AXA Chair on Sand and Dust Storms at the Barcelona Supercomputing Center (BSC), the European Union’s Horizon2020 research and innovation program under grant agreement no. 821205 (FORCeS) and national grants HEAVY PID2022-140365OB-I00 and BIOTA PID2022., Objectius de Desenvolupament Sostenible::13 - Acció per al Clima, Postprint (published version)

Published
2024

9. Light-absorbing black carbon and brown carbon components of smoke aerosol from DSCOVR EPIC measurements over North America and Central Africa.

Author

Myungje Choi, Alexei Lyapustin, Schuster, Gregory L., Sujung Go, Yujie Wang, Korkin, Sergey, Kahn, Ralph, Reid, Jeffrey S., Hyer, Edward J., Eck, Thomas F., Mian Chin, Diner, David J., Kalashnikova, Olga, Dubovik, Oleg, Jhoon Kim, and Moosmüller, Hans

Abstract

Wildfires and agricultural burning generate seemingly increasing smoke aerosol emissions, impacting societal and natural ecosystems. To understand smoke's effects on climate and public health, we analyzed the spatiotemporal distribution of smoke aerosols, focusing on two major light-absorbing components, black carbon (BC) and brown carbon (BrC) aerosols. Using NASA's Earth Polychromatic Imaging Camera (EPIC) instrument aboard the NOAA's Deep Space Climate Observatory (DSCOVR) spacecraft, we inferred BC and BrC volume fractions and particle mass concentrations based on spectral absorption provided by the Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm with 1-2 hours temporal resolution and ~10 km spatial resolution over North America and Central Africa. Our analyses of regional smoke properties reveal distinct characteristics for aerosol optical depth (AOD) at 443 nm, spectral single scattering albedo (SSA), aerosol layer height (ALH), and BC and BrC amounts. Smoke cases in North America show extremely high AOD up to 6, with elevated ALH (6-7 km) and significant BrC components up to 250 mg/m2 along the transport paths, whereas the smoke aerosols in Central Africa exhibited stronger light absorption (i.e., lower SSA) and lower AOD, resulting in higher BC mass concentrations and similar BrC mass concentrations than the cases in North America. Seasonal burning source locations in Central Africa following the seasonal shift of Inter Tropical Convergence Zone and diurnal variations in smoke amounts were also captured. Comparison of retrieved AOD443, SSA443, SSA680, and ALH with collocated AERONET and CALIOP measurements shows agreement with rmse of 0.2, 0.03-0.04, 0.02-0.04, and 0.8-1.3 km, respectively. Analysis of spatiotemporally average reveals distinct geographical characteristics in smoke properties closely linked to burning types and meteorological conditions. Forest wildfires over western North America generated smoke with small BC volume fraction of 0.011 and high ALH with large variability (2.2 ± 1.2 km), whereas smoke from wildfires and agricultural burning over Mexico region shows more absorption and low ALH. Smoke from savanna fires over Central Africa has the most absorption with high BC volume fraction (0.015) and low ALH with small variation (1.8 ± 0.6 km) among the analyzed regions. Tropical forest smoke was less absorbing and had a high variance in ALH. We also quantify the estimation uncertainties related to the assumptions of BC and BrC refractive indices. The MAIAC EPIC smoke properties with BC and BrC volume and mass fractions and assessment of layer height provide observational constraints for radiative forcing modeling and air quality and health studies. [ABSTRACT FROM AUTHOR]

Published
2024
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10. Observationally constrained regional variations of shortwave absorption by iron oxides emphasize the cooling effect of dust.

Author

Obiso, Vincenzo, Gonçalves Ageitos, María, Pérez García-Pando, Carlos, Perlwitz, Jan P., Schuster, Gregory L., Bauer, Susanne E., Di Biagio, Claudia, Formenti, Paola, Tsigaridis, Kostas, and Miller, Ron L.

Subjects
MINERAL dusts, IRON oxides, DUST, SOIL mineralogy, GLOBAL cooling, AEROSOL sampling
Abstract

The composition of soil dust aerosols derives from the mineral abundances in the parent soils that vary across dust source regions. Nonetheless, Earth system models (ESMs) have traditionally represented mineral dust as a globally homogeneous species. The growing interest in modeling dust mineralogy, facilitated by the recognized sensitivity of the dust climate impacts to composition, has motivated state-of-the-art ESMs to incorporate the mineral speciation of dust along with its effect upon the dust direct radiative effect (DRE). In this work, we enable the NASA Goddard Institute for Space Studies ModelE2.1 to calculate the shortwave (SW) DRE accounting for the regionally varying soil mineralogy. Mineral–radiation interaction at solar wavelengths is calculated according to two alternative coupling schemes: (1) external mixing of three mineral components that are optically distinguished, one of which contains embedded iron oxides; (2) a single internal mixture of all dust minerals with a dynamic fraction of iron oxides that varies regionally and temporally. We link dust absorption to the fractional mass of iron oxides based on recent chamber measurements using natural dust aerosol samples. We show that coupled mineralogy overall enhances the scattering by dust, and thus the global cooling, compared to our control run with globally uniform composition. According to the external mixing scheme, the SW DRE at the top of atmosphere (TOA) changes from -0.25 to -0.30Wm-2 , corresponding to a change in the net DRE, including the longwave effect, from -0.08 to -0.12Wm-2. The cooling increase is accentuated when the internal mixing scheme is configured: the SW DRE at the TOA becomes -0.34Wm-2 with a net DRE of -0.15Wm-2. The varying composition modifies the regional distribution of single scattering albedo (SSA), whose variations in specific regions can be remarkable (above 0.03) and significantly modify the regional SW DRE. Evaluation against the AErosol RObotic NETwork (AERONET) shows that explicit representation of soil mineralogy and its regional variations reduces the low bias of model dust SSA while improving the range of variability across stations and calendar months. Despite these improvements, the moderate spatiotemporal correlation with AERONET reveals remaining modeling challenges and the need for more accurate measurements of mineral fractions in soils. [ABSTRACT FROM AUTHOR]

Published
2024
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12. Observationally constrained regional variations of shortwave absorption by iron oxides emphasize the cooling effect of dust

Author

Obiso, Vincenzo, Gonçalves Ageitos, María, Pérez García-Pando, Carlos, Schuster, Gregory L., Bauer, Susanne E., Biagio, Claudia, Formenti, Paola, Perlwitz, Jan P., Tsigaridis, Konstantinos, and Miller, Ronald L.

Abstract

The composition of soil dust aerosols derives from the mineral abundances in the parent soils that vary across dust source regions. Nonetheless, Earth System Models (ESMs) have traditionally represented mineral dust as a globally homogeneous species. The growing interest in modeling dust mineralogy, facilitated by the recognized sensitivity of the dust climate impacts to composition, has motivated state-of-the-art ESMs to incorporate the mineral speciation of dust along with its effect upon the dust direct radiative effect (DRE). In this work, we enable the NASA Goddard Institute for Space Studies ModelE2.1 to calculate the shortwave (SW) DRE by accounting for the regionally varying soil mineralogy. Mineral-radiation interaction at solar wavelengths is calculated according to two alternative coupling schemes: 1) external mixing of three mineral components that are optically distinguished, one of which contains embedded iron oxides; 2) a single internal mixture of all dust minerals with a dynamic fraction of iron oxides that varies regionally and temporally. We link dust absorption to the fractional mass of iron oxides based on recent chamber measurements using natural dust aerosol samples. We show that coupled mineralogy overall enhances the scattering by dust, and thus the global cooling, compared to our control run with globally uniform composition. According to the external mixing scheme, the SW DRE at the top of atmosphere (TOA) changes from -0.25 to -0.30 W · m-2, corresponding to a change in the net DRE, including the longwave effect, from -0.08 to -0.12 W · m-2. The cooling increase is accentuated when the internal mixing scheme is configured: SW DRE at TOA becomes -0.34 W · m-2 (with a net DRE of -0.15 W · m-2). The varying composition modifies the regional distribution of single scattering albedo (SSA), whose variations in specific regions can be remarkable (above 0.03) and significantly modify the regional DRE. Evaluation against the AErosol RObotic NETwork (AERONET) shows that explicit representation of soil mineralogy and its regional variations reduces the low bias of model dust SSA, while improving the range of variability across stations and calendar months. Despite these improvements, the moderate spatio-temporal correlation with AERONET reveals remaining modeling challenges and the need for more accurate measurements of mineral fractions in soils.

Published
2023

13. Modeling atmospheric brown carbon in the GISS ModelE Earth system model.

Author

DeLessio, Maegan A., Tsigaridis, Kostas, Bauer, Susanne E., Chowdhary, Jacek, and Schuster, Gregory L.

Subjects
ATMOSPHERIC models, BIOMASS burning, RADIATIVE forcing, VOLATILE organic compounds, CARBON-black
Abstract

Brown carbon (BrC) is an absorbing organic aerosol, primarily emitted through biomass burning, that exhibits light absorption unique from both black carbon (BC) and other organic aerosols (OA). Despite many field and laboratory studies seeking to constrain BrC properties, the radiative forcing of BrC is still highly uncertain. To better understand it's climate impact, we introduced BrC to the One-Moment Aerosol (OMA) module of the GISS ModelE Earth system model (ESM). We assessed ModelE sensitivity to primary BrC processed through a novel chemical aging scheme, as well as secondary BrC formed from biogenic volatile organic compounds (BVOCs). Initial results show BrC typically contributes a top of the atmosphere (TOA) radiative effect of 0.04 W m-2. Sensitivity tests indicate that explicitly simulating BrC (separating it from other OA), including secondary BrC, and simulating chemical bleaching of BrC all contribute distinguishable radiative effects and should be accounted for in BrC schemes. This addition of prognostic BrC to ModelE allows for greater physical and chemical complexity in OA representation with no apparent trade-off in model performance as evaluation of ModelE aerosol optical depth, with and without the BrC scheme, against AERONET and MODIS retrieval data reveals similar skill in both cases. Thus, BrC should be explicitly simulated to allow for more physically based chemical composition, which is crucial for more detailed OA study like comparisons to in-situ measurement campaigns. We include additional recommendations for BrC representation within ESMs at the end of this paper. [ABSTRACT FROM AUTHOR]

Published
2023
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15. Characteristics of In Situ Fine Fraction Aerosol Spectra from 300-700 nm Observed Around the Korean Peninsula During KORUS-OC

Author

Jordan, Carolyn E, Schuster, Gregory L, Stauffer, Ryan M, Lamb, Brian Thomas, Novak, Michael, Mannino, Antonio, Hudgins, Charles, Thornhill, Kenneth Lee, Crosbie, Ewan, Winstead, Edward, Anderson, Bruce, Martin, Robert, Shook, Michael, Ziemba, Luke D, Beyersdorf, Andreas Joel, and Corr, Chelsea

Subjects
Environment Pollution
Abstract

In situ aerosol extinction and absorption spectra covering the 300-700 nm range at ≤ 1 nm spectral resolution were measured aboard the R/V Onnuri during the Korea U.S. – Ocean Color (KORUS-OC) cruise around the Korean Peninsula from May 21 through June 3, 2016. Total absorption spectra were obtained from aerosols collected on glass fiber filters and subsequently placed in the center of an integrating sphere (Labsphere DRA-CA-30) attached to a dual beam spectrophotometer (Cary 100 Bio UV-Visible Spectrophotometer, 0.2 nm spectral resolution). Absorption spectra from methanol and deionized water extracts of aerosols collected on Teflon filters were measured in a liquid waveguide capillary cell (World Precision Instruments LWCC- 3100, ~0.4 nm spectral resolution). Extinction spectra were measured with a custom built instrument (SpEx, ~0.8 nm spectral resolution). The measurements were obtained at a height of ~10 m above the sea surface with an inlet that limited the measured aerosols to diameters ≤ 1.3 µm. All four sets of spectra exhibit curvature in log-log space with 2nd order polynomials providing a better fit to the measured spectra than power law fits. The deionized water extracts were also analyzed with an ion chromatograph (Dionex ICS-3000 Ion Chromatography System) and with an aerosol mass spectrometer (Aerodyne Research, Inc. HR-ToF High Resolution Aerosol Mass Spectrometer) to examine chemical composition. These data indicate the optical spectra are sensitive to differing chemical properties of the measured ambient aerosols and suggest differing sources and/or atmospheric processes influence the observed optical signatures. The measured suite of spectra are combined to examine the spectral characteristics of single scattering albedo, as well as to examine the contribution of soluble absorbing chromophores to the total absorption spectra. Additional measurements made during the affiliated Korea U.S. - Air Quality (KORUS-AQ) campaign will be used to provide further insight on the observed spectral characteristics.

Published
2018

16. Beyond the Ångström Exponent: Probing Additional Information in Spectral Curvature and Variability of In Situ Aerosol Hyperspectral (0.3–0.7 μm) Optical Properties

Author

Jordan, Carolyn E., primary, Anderson, Bruce E., additional, Barrick, John D., additional, Blum, Dani, additional, Brunke, Kathleen, additional, Chai, Jiajue, additional, Chen, Gao, additional, Crosbie, Ewan C., additional, Dibb, Jack E., additional, Dillner, Ann M., additional, Gargulinski, Emily, additional, Hudgins, Charles H., additional, Joyce, Emily, additional, Kaspari, Jackson, additional, Martin, Robert F., additional, Moore, Richard H., additional, O’Brien, Rachel, additional, Robinson, Claire E., additional, Schuster, Gregory L., additional, Shingler, Taylor J., additional, Shook, Michael A., additional, Soja, Amber J., additional, Thornhill, Kenneth L., additional, Weakley, Andrew T., additional, Wiggins, Elizabeth B., additional, Winstead, Edward L., additional, and Ziemba, Luke D., additional

Published
2022
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17. Spatial Representativeness Error in the Ground-Level Observation Networks for Black Carbon Radiation Absorption

Author

Wang, Rong, Andrews, Elisabeth, Balkanski, Yves, Boucher, Olivier, Myhre, Gunnar, Samset, Bjørn Hallvard, Schulz, Michael, Schuster, Gregory L, Valari, Myrto, and Tao, Shu

Subjects
Earth Resources And Remote Sensing
Abstract

There is high uncertainty in the direct radiative forcing of black carbon (BC), an aerosol that strongly absorbs solar radiation. The observation-constrained estimate, which is several times larger than the bottom-up estimate, is influenced by the spatial representativeness error due to the mesoscale inhomogeneity of the aerosol fields and the relatively low resolution of global chemistry-transport models. Here we evaluated the spatial representativeness error for two widely used observational networks (AErosol RObotic NETwork and Global Atmosphere Watch) by downscaling the geospatial grid in a global model of BC aerosol absorption optical depth to 0.1° × 0.1°. Comparing the models at a spatial resolution of 2° × 2° with BC aerosol absorption at AErosol RObotic NETwork sites (which are commonly located near emission hot spots) tends to cause a global spatial representativeness error of 30%, as a positive bias for the current top-down estimate of global BC direct radiative forcing. By contrast, the global spatial representativeness error will be 7% for the Global Atmosphere Watch network, because the sites are located in such a way that there are almost an equal number of sites with positive or negative representativeness error.

Published
2018
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19. Climatology of aerosol component concentrations derived from multi-angular polarimetric POLDER-3 observations using GRASP algorithm

Author

Li, Lei, primary, Derimian, Yevgeny, additional, Chen, Cheng, additional, Zhang, Xindan, additional, Che, Huizheng, additional, Schuster, Gregory L., additional, Fuertes, David, additional, Litvinov, Pavel, additional, Lapyonok, Tatyana, additional, Lopatin, Anton, additional, Matar, Christian, additional, Ducos, Fabrice, additional, Karol, Yana, additional, Torres, Benjamin, additional, Gui, Ke, additional, Zheng, Yu, additional, Liang, Yuanxin, additional, Lei, Yadong, additional, Zhu, Jibiao, additional, Zhang, Lei, additional, Zhong, Junting, additional, Zhang, Xiaoye, additional, and Dubovik, Oleg, additional

Published
2022
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20. Climatology of aerosol components concentration derived by GRASP algorithm from multi-angular polarimetric POLDER-3 observations

Author

Li, Lei, primary, Derimian, Yevgeny, additional, Chen, Cheng, additional, Zhang, Xindan, additional, Che, Huizheng, additional, Schuster, Gregory L., additional, Fuertes, David, additional, Litvinov, Pavel, additional, Lapyonok, Tatyana, additional, Lopatin, Anton, additional, Matar, Christian, additional, Ducos, Fabrice, additional, Karol, Yana, additional, Torres, Benjamin, additional, Gui, Ke, additional, Zheng, Yu, additional, Liang, Yuanxin, additional, Lei, Yadong, additional, Zhu, Jibiao, additional, Zhang, Lei, additional, Zhong, Junting, additional, Zhang, Xiaoye, additional, and Dubovik, Oleg, additional

Published
2022
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21. Identifying chemical aerosol signatures using optical suborbital observations: how much can optical properties tell us about aerosol composition?

Author

Kacenelenbogen, Meloë S. F., primary, Tan, Qian, additional, Burton, Sharon P., additional, Hasekamp, Otto P., additional, Froyd, Karl D., additional, Shinozuka, Yohei, additional, Beyersdorf, Andreas J., additional, Ziemba, Luke, additional, Thornhill, Kenneth L., additional, Dibb, Jack E., additional, Shingler, Taylor, additional, Sorooshian, Armin, additional, Espinosa, Reed W., additional, Martins, Vanderlei, additional, Jimenez, Jose L., additional, Campuzano-Jost, Pedro, additional, Schwarz, Joshua P., additional, Johnson, Matthew S., additional, Redemann, Jens, additional, and Schuster, Gregory L., additional

Published
2022
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22. Aerosol Absorption Retrieval at Ultraviolet Wavelengths in a Complex Environment

Author

Kazadzis, Stelios, Raptis, Panagiotis, Kouremeti, Natalia, Amirdis, Vassilis, Arola, Antti, Gerasopoulos, Evangelos, and Schuster, Gregory L

Subjects
Earth Resources And Remote Sensing
Abstract

We have used total and diffuse UV irradiance measurements from a multi-filter rotating shadow-band radiometer (UVMFR) in order to investigate aerosol absorption in the UV range for a 5-year period in Athens, Greece. This dataset was used as input to a radiative transfer model and the single scattering albedo (SSA) at 368 and 332 nm was calculated. Retrievals from a collocated CIMEL sun photometer were used to evaluate the products and study the absorption spectral behavior of retrieved SSA values. The UVMFR SSA, together with synchronous, CIMEL-derived retrievals of SSA at 440 nm, had a mean of 0.90, 0.87 and 0.83, with lowest values (higher absorption) encountered at the shorter wavelengths. In addition, noticeable diurnal variation of the SSA in all wavelengths is shown, with amplitudes up to 0.05. Strong SSA wavelength dependence is revealed for cases of low Angstrom exponents, accompanied by a SSA decrease with decreasing extinction optical depth, suggesting varying influence under different aerosol composition. However, part of this dependence for low aerosol optical depths is masked by the enhanced SSA retrieval uncertainty. Dust and brown carbon UV absorbing properties were also investigated to explain seasonal patterns.

Published
2016
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25. A Comprehensive Description of Multi-Term LSM for Applying Multiple a Priori Constraints in Problems of Atmospheric Remote Sensing: GRASP Algorithm, Concept, and Applications

Author

Dubovik, Oleg, primary, Fuertes, David, additional, Litvinov, Pavel, additional, Lopatin, Anton, additional, Lapyonok, Tatyana, additional, Doubovik, Ivan, additional, Xu, Feng, additional, Ducos, Fabrice, additional, Chen, Cheng, additional, Torres, Benjamin, additional, Derimian, Yevgeny, additional, Li, Lei, additional, Herreras-Giralda, Marcos, additional, Herrera, Milagros, additional, Karol, Yana, additional, Matar, Christian, additional, Schuster, Gregory L., additional, Espinosa, Reed, additional, Puthukkudy, Anin, additional, Li, Zhengqiang, additional, Fischer, Juergen, additional, Preusker, Rene, additional, Cuesta, Juan, additional, Kreuter, Axel, additional, Cede, Alexander, additional, Aspetsberger, Michael, additional, Marth, Daniel, additional, Bindreiter, Lukas, additional, Hangler, Andreas, additional, Lanzinger, Verena, additional, Holter, Christoph, additional, and Federspiel, Christian, additional

Published
2021
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26. Identifying Chemical Aerosol Signatures using Optical Suborbital Observations: How much can optical properties tell us about aerosol composition?

Author

Kacenelenbogen, Meloë S. F., primary, Tan, Qian, additional, Burton, Sharon P., additional, Hasekamp, Otto P., additional, Froyd, Karl D., additional, Shinozuka, Yohei, additional, Beyersdorf, Andreas J., additional, Ziemba, Luke, additional, Thornhill, Kenneth L., additional, Dibb, Jack E., additional, Shingler, Taylor, additional, Sorooshian, Armin, additional, Espinosa, Reed W., additional, Martins, Vanderlei, additional, Jimenez, Jose L., additional, Campuzano-Jost, Pedro, additional, Schwarz, Joshua P., additional, Johnson, Matthew S., additional, Redemann, Jens, additional, and Schuster, Gregory L., additional

Published
2021
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27. Understanding Top‐of‐Atmosphere Flux Bias in the AeroCom Phase III Models: A Clear‐Sky Perspective

Author

Su, Wenying, primary, Liang, Lusheng, additional, Myhre, Gunnar, additional, Thorsen, Tyler J., additional, Loeb, Norman G., additional, Schuster, Gregory L., additional, Ginoux, Paul, additional, Paulot, Fabien, additional, Neubauer, David, additional, Checa‐Garcia, Ramiro, additional, Matsui, Hitoshi, additional, Tsigaridis, Kostas, additional, Skeie, Ragnhild B., additional, Takemura, Toshihiko, additional, Bauer, Susanne E., additional, and Schulz, Michael, additional

Published
2021
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29. Supplementary material to "Inferring iron oxides species content in atmospheric mineral dust from DSCOVR EPIC observations"

Author

Go, Sujung, primary, Lyapustin, Alexei, additional, Schuster, Gregory L., additional, Choi, Myungje, additional, Ginoux, Paul, additional, Chin, Mian, additional, Kalashnikova, Olga, additional, Dubovik, Oleg, additional, Kim, Jhoon, additional, Silva, Arlindo da, additional, Holben, Brent, additional, and Reid, Jeffrey S., additional

Published
2021
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30. Active remote sensing of atmospheric dust using relationships between their depolarization ratios and reflectivity

Author

Zubko, Evgenij, primary, Shmirko, Konstantin, additional, Pavlov, Andrey, additional, Sun, Wenbo, additional, Schuster, Gregory L., additional, Hu, Yongxiang, additional, Stamnes, Snorre, additional, Omar, Ali, additional, Baize, Rosemary R., additional, McCormick, M. Patrick, additional, Loughman, Robert, additional, Arnold, Jessica A., additional, and Videen, Gorden, additional

Published
2021
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31. Remote sensing of aerosol water fraction, dry size distribution and soluble fraction using multi-angle, multi-spectral polarimetry.

Author

Diedenhoven, Bastiaan van, Hasekamp, Otto P., Cairns, Brian, Schuster, Gregory L., Stammes, Snorre, Shook, Michael A., and Ziemba, Luke D.

Subjects
REMOTE sensing, ATMOSPHERIC aerosols, POLARIMETRY, PARTICLE size distribution, ATMOSPHERIC models
Abstract

A framework to infer volume water fraction, soluble fraction and dry size distributions of fine mode aerosol from multi-angle, multi-spectral polarimetry retrievals of column-averaged ambient aerosol properties is presented. The method is applied to observations of the Research Scanning Polarimeter (RSP) obtained during two NASA aircraft campaigns, namely the Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) and the Cloud, Aerosol, and Monsoon Processes-Philippines Experiment (CAMP2Ex). All aerosol retrievals are statistically evaluated using in situ data. Volume water fraction is inferred from the retrieved ambient real part of the refractive index, assuming a dry refractive index of 1.54 and by applying a volume mixing rule to obtain the effective ambient refractive index. The uncertainties in inferred volume water fraction resulting from this simplified model are discussed and estimated to be lower than 0.2 and decreasing with increasing volume water fraction. The daily mean retrieved volume water fractions correlate well with the in situ values with a mean absolute difference of 0.09. Polarimeter-retrieved ambient effective radius for daily data is shown to increase as a function of volume water fraction as expected. Furthermore, the effective variance of the size distributions also increases with increasing effective radius, which we show is consistent with an external mixture of soluble and insoluble aerosol. The relative variations of effective radius and variance over an observation period are then used to estimate the soluble fraction of the aerosol. Daily results of soluble fraction correlate well with in situ observed sulfate mass fraction with a correlation coefficient of 0.79. Subsequently, inferred water and soluble fractions are used to derive dry fine-mode size distributions from their ambient counterparts. While dry effective radii obtained in situ and from RSP show similar ranges, in situ values are generally substantially smaller during the ACTIVATE deployments, which may be due to biases in RSP retrievals or in the in situ observations, or both. Both RSP and in situ observations indicate the dominance of aerosol with low hygroscopicity during the ACTIVATE and CAMP2Ex campaigns. Furthermore, RSP indicates a high degree of external mixing of particles with low and high hygroscopicity. These retrievals of fine mode water volume fraction and soluble fraction may be used for the evaluation of water uptake in atmospheric models. Furthermore, the framework allows to estimate the variation in the concentration of fine-mode aerosol larger than a specific dry radius limit, which can be used as a proxy for the variation in cloud condensation nucleus concentrations. This framework may be applied to multi-angle, multi-spectral satellite data expected to be available in the near future. [ABSTRACT FROM AUTHOR]

Published
2022
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33. Classification of Aerosol Retrievals from Spaceborne Polarimetry Using a Multiparameter Algorithm

Author

Russell, Philip B, Kacenelenbogen, Meloe, Livingston, John M, Hasekamp, Otto P, Burton, Sharon P, Schuster, Gregory L, Johnson, Matthew S, Knobelspiesse, Kirk D, Redemann, Jens, Ramachandran, S, and Holben, Brent

Subjects
Earth Resources And Remote Sensing
Abstract

In this presentation, we demonstrate application of a new aerosol classification algorithm to retrievals from the POLDER-3 polarimter on the PARASOL spacecraft. Motivation and method: Since the development of global aerosol measurements by satellites and AERONET, classification of observed aerosols into several types (e.g., urban-industrial, biomass burning, mineral dust, maritime, and various subtypes or mixtures of these) has proven useful to: understanding aerosol sources, transformations, effects, and feedback mechanisms; improving accuracy of satellite retrievals and quantifying assessments of aerosol radiative impacts on climate.

Published
2013

35. New in situ aerosol hyperspectral optical measurements over 300–700 nm – Part 1: Spectral Aerosol Extinction (SpEx) instrument field validation during the KORUS-OC cruise

Author

Jordan, Carolyn E., primary, Stauffer, Ryan M., additional, Lamb, Brian T., additional, Hudgins, Charles H., additional, Thornhill, Kenneth L., additional, Schuster, Gregory L., additional, Moore, Richard H., additional, Crosbie, Ewan C., additional, Winstead, Edward L., additional, Anderson, Bruce E., additional, Martin, Robert F., additional, Shook, Michael A., additional, Ziemba, Luke D., additional, Beyersdorf, Andreas J., additional, Robinson, Claire E., additional, Corr, Chelsea A., additional, and Tzortziou, Maria A., additional

Published
2021
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36. New in situ aerosol hyperspectral optical measurements over 300–700 nm – Part 2: Extinction, total absorption, water- and methanol-soluble absorption observed during the KORUS-OC cruise

Author

Jordan, Carolyn E., primary, Stauffer, Ryan M., additional, Lamb, Brian T., additional, Novak, Michael, additional, Mannino, Antonio, additional, Crosbie, Ewan C., additional, Schuster, Gregory L., additional, Moore, Richard H., additional, Hudgins, Charles H., additional, Thornhill, Kenneth L., additional, Winstead, Edward L., additional, Anderson, Bruce E., additional, Martin, Robert F., additional, Shook, Michael A., additional, Ziemba, Luke D., additional, Beyersdorf, Andreas J., additional, Robinson, Claire E., additional, Corr, Chelsea A., additional, and Tzortziou, Maria A., additional

Published
2021
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37. Climatology of aerosol components concentration derived by GRASP algorithm from multi-angular polarimetric POLDER-3 observations.

Author

Lei Li, Yevgeny Derimian, Cheng Chen, Xindan Zhang, Huizheng Che, Schuster, Gregory L., Fuertes, David, Litvinov, Pavel, Lapyonok, Tatyana, Lopatin, Anton, Matar, Christian, Ducos, Fabrice, Karol, Yana, Torres, Benjamin, Ke Gui, Yu Zheng, Yuanxin Liang, Yadong Lei, Jibiao Zhu, and Lei Zhang

Subjects
MINERAL dusts, CARBONACEOUS aerosols, AEROSOLS, CLIMATOLOGY, BIOMASS burning, AMMONIUM sulfate, IRON oxides
Abstract

The study presents a climatology of aerosol composition concentration obtained by a recently developed GRASP/Component (GRASP stands for the Generalized Retrieval of Atmosphere and Surface Properties algorithm) approach applied to the whole archive of POLDER-3 observations. The conceptual specific of the GRASP/Component approach is in direct retrieval of aerosol speciation (component fraction) without an intermediate retrievals of aerosol optical characteristics. Despite a global validation of the derived aerosol component product is challenging, the results obtained are in line with general knowledge about aerosol types in different regions. In addition, we compare the GRASP derived black carbon and dust components with those of the MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, version 2) product. Quite reasonable general agreement in spatial and temporal distribution of the species provided by GRASP and MERRA-2 was found, the differences however appeared in regions known for strong biomass burning and dust emissions; the reasons for the discrepancies are discussed. The other derived components, such as concentration of absorbing (black carbon, brown carbon, iron oxides content in mineral dust) and scattering (ammonium sulphate and nitrate, organic carbon, non-absorbing dust) aerosol, represent scarce but imperative information for validation and potential adjustment of chemical transport models. The aerosol optical properties derived by GRASP/Component were found to agree well with the AERONET ground reference data and fully consistent with the previous GRASP Optimized, High Precision and Models retrieval versions applied to POLDER-3 data. Thus, the presented extensive climatology product provides an opportunity for understanding variabilities and trends in global and regional distributions of aerosol species. The climatology of the aerosol components obtained in addition to the aerosol optical properties provides additional valuable, qualitatively new inside about aerosol distributions and, therefore, demonstrates advantages of multi-angular polarimetric satellite observations as the next frontier for aerosol inversion from advanced satellite observations. [ABSTRACT FROM AUTHOR]

Published
2022
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39. New In Situ Aerosol Hyperspectral Optical Measurements over 300–700 nm, Part 1: Spectral Aerosol Extinction (SpEx) Instrument Field Validation during the KORUS-OC cruise

Author

Jordan, Carolyn E., primary, Stauffer, Ryan M., additional, Lamb, Brian T., additional, Hudgins, Charles H., additional, Thornhill, Kenneth L., additional, Schuster, Gregory L., additional, Moore, Richard H., additional, Crosbie, Ewan C., additional, Winstead, Edward L., additional, Anderson, Bruce E., additional, Martin, Robert F., additional, Shook, Michael A., additional, Ziemba, Luke D., additional, Beyersdorf, Andreas J., additional, Robinson, Claire E., additional, Corr, Chelsea A., additional, and Tzortziou, Maria A., additional

Published
2020
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40. Supplementary material to "New In Situ Aerosol Hyperspectral Optical Measurements over 300–700 nm, Part 2: Extinction, Total Absorption, Water- and Methanol-soluble Absorption observed during the KORUS-OC cruise"

Author

Jordan, Carolyn E., primary, Stauffer, Ryan M., additional, Lamb, Brian T., additional, Novak, Michael, additional, Mannino, Antonio, additional, Crosbie, Ewan C., additional, Schuster, Gregory L., additional, Moore, Richard H., additional, Hudgins, Charles H., additional, Thornhill, Kenneth L., additional, Winstead, Edward L., additional, Anderson, Bruce E., additional, Martin, Robert F., additional, Shook, Michael A., additional, Ziemba, Luke D., additional, Beyersdorf, Andreas J., additional, Robinson, Claire E., additional, Corr, Chelsea A., additional, and Tzortziou, Maria A., additional

Published
2020
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41. New In Situ Aerosol Hyperspectral Optical Measurements over 300–700 nm, Part 2: Extinction, Total Absorption, Water- and Methanol-soluble Absorption observed during the KORUS-OC cruise

Author

Jordan, Carolyn E., primary, Stauffer, Ryan M., additional, Lamb, Brian T., additional, Novak, Michael, additional, Mannino, Antonio, additional, Crosbie, Ewan C., additional, Schuster, Gregory L., additional, Moore, Richard H., additional, Hudgins, Charles H., additional, Thornhill, Kenneth L., additional, Winstead, Edward L., additional, Anderson, Bruce E., additional, Martin, Robert F., additional, Shook, Michael A., additional, Ziemba, Luke D., additional, Beyersdorf, Andreas J., additional, Robinson, Claire E., additional, Corr, Chelsea A., additional, and Tzortziou, Maria A., additional

Published
2020
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42. Supplementary material to "New In Situ Aerosol Hyperspectral Optical Measurements over 300–700 nm, Part 1: Spectral Aerosol Extinction (SpEx) Instrument Field Validation during the KORUS-OC cruise"

Author

Jordan, Carolyn E., primary, Stauffer, Ryan M., additional, Lamb, Brian T., additional, Hudgins, Charles H., additional, Thornhill, Kenneth L., additional, Schuster, Gregory L., additional, Moore, Richard H., additional, Crosbie, Ewan C., additional, Winstead, Edward L., additional, Anderson, Bruce E., additional, Martin, Robert F., additional, Shook, Michael A., additional, Ziemba, Luke D., additional, Beyersdorf, Andreas J., additional, Robinson, Claire E., additional, Corr, Chelsea A., additional, and Tzortziou, Maria A., additional

Published
2020
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43. Constraining global aerosol emissions using POLDER/PARASOL satellite remote sensing observations

Author

Chen, Cheng, primary, Dubovik, Oleg, additional, Henze, Daven K., additional, Chin, Mian, additional, Lapyonok, Tatyana, additional, Schuster, Gregory L., additional, Ducos, Fabrice, additional, Fuertes, David, additional, Litvinov, Pavel, additional, Li, Lei, additional, Lopatin, Anton, additional, Hu, Qiaoyun, additional, and Torres, Benjamin, additional

Published
2019
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44. Retrieval of aerosol composition directly from satellite and ground-based measurements

Author

Li, Lei, Dubovik, Oleg, Derimian, Yevgeny, Schuster, Gregory L., Lapyonok, Tatyana, Litvinov, Pavel, Ducos, Fabrice, Fuertes, David, Chen, Cheng, Li, Zhengqiang, Lopatin, Anton, Torres, Benjamin, and Che, Huizheng

Subjects
respiratory system, complex mixtures, Physics::Atmospheric and Oceanic Physics
Abstract

This study presents a novel methodology for remote monitoring of aerosol composition over large spatial and temporal domains. The concept is realized within the GRASP (Generalized Retrieval of Aerosol and Surface Properties) algorithm to directly infer aerosol composition from the measured radiances. This approach is different from the conventional methods that use post-processing of the retrieved aerosol optical properties for aerosol typing. The proposed method assumes observed aerosols as mixtures of particles composed of black carbon, brown carbon, absorbing insoluble, non-absorbing insoluble embedded in a soluble host. The algorithm then derives size distribution and the fractions of these components. The complex refractive index of each component is fixed a priori and the complex refractive index of mixture is computed using mixing rules. The approach is first tested with synthetic data and the uncertainties are estimated. Then, it is applied to the real ground-based AERONET and space-borne POLDER/PARASOL observations, known to be sensitive to aerosol complex refractive index. The study presents a first attempt to derive aerosol composition from satellites. The obtained aerosol optical characteristics are highly consistent with the standard products (R of ~ 0.9 for aerosol optical thickness). The approach also presented an ability to separate between aerosol properties in fine and coarse size fractions, in case of POLDER/PARASOL and AERONET. Examples of application to POLDER/PARASOL on the global scale are presented. The obtained spatial and temporal patterns of the aerosol composition agree well with our knowledge on aerosol sources and transport features. Finally, limitations and perspectives are discussed.

Published
2019

45. Aerosol and Cloud Interaction Observed From High Spectral Resolution Lidar Data

Author

Su, Wenying, Schuster, Gregory L, Loeb, Norman G, Rogers, Raymond R, Ferrare, Richard A, Hostetler, Chris A, Hair, Johnathan W, and Obland, Michael D

Subjects
Meteorology And Climatology
Abstract

Recent studies utilizing satellite retrievals have shown a strong correlation between aerosol optical depth (AOD) and cloud cover. However, these retrievals from passive sensors are subject to many limitations, including cloud adjacency (or 3D) effects, possible cloud contamination, uncertainty in the AOD retrieval. Some of these limitations do not exist in High Spectral Resolution Lidar (HSRL) observations; for instance, HSRL observations are not a ected by cloud adjacency effects, are less prone to cloud contamination, and offer accurate aerosol property measurements (backscatter coefficient, extinction coefficient, lidar ratio, backscatter Angstrom exponent,and aerosol optical depth) at a neospatial resolution (less than 100 m) in the vicinity of clouds. Hence, the HSRL provides an important dataset for studying aerosol and cloud interaction. In this study, we statistically analyze aircraft-based HSRL profiles according to their distance from the nearest cloud, assuring that all profile comparisons are subject to the same large-scale meteorological conditions. Our results indicate that AODs from HSRL are about 17% higher in the proximity of clouds (approximately 100 m) than far away from clouds (4.5 km), which is much smaller than the reported cloud 3D effect on AOD retrievals. The backscatter and extinction coefficients also systematically increase in the vicinity of clouds, which can be explained by aerosol swelling in the high relative humidity (RH) environment and/or aerosol growth through in cloud processing (albeit not conclusively). On the other hand, we do not observe a systematic trend in lidar ratio; we hypothesize that this is caused by the opposite effects of aerosol swelling and aerosol in-cloud processing on the lidar ratio. Finally, the observed backscatter Angstrom exponent (BAE) does not show a consistent trend because of the complicated relationship between BAE and RH. We demonstrate that BAE should not be used as a surrogate for Angstrom exponent, especially at high RH.

Published
2008
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46. An Observational Study of the Relationship between Cloud, Aerosol and Meteorology in Broken Low-Level Cloud Conditions

Author

Loeb, Norman G and Schuster, Gregory L

Subjects
Meteorology And Climatology
Abstract

Global satellite analyses showing strong correlations between aerosol optical depth and 3 cloud cover have stirred much debate recently. While it is tempting to interpret the results as evidence of aerosol enhancement of cloud cover, other factors such as the influence of meteorology on both the aerosol and cloud distributions can also play a role, as both aerosols and clouds depend upon local meteorology. This study uses satellite observations to examine aerosol-cloud relationships for broken low-level cloud regions off the coast of Africa. The analysis approach minimizes the influence of large-scale meteorology by restricting the spatial and temporal domains in which the aerosol and cloud properties are compared. While distributions of several meteorological variables within 5deg 5deg latitude-longitude regions are nearly identical under low and high aerosol optical depth, the corresponding distributions of single-layer low cloud properties and top-of-atmosphere radiative fluxes differ markedly, consistent with earlier studies showing increased cloud cover with aerosol optical depth. Furthermore, fine-mode fraction and Angstrom Exponent are also larger in conditions of higher aerosol optical depth, even though no evidence of systematic latitudinal or longitudinal gradients between the low and high aerosol optical depth populations are observed. When the analysis is repeated for all 5deg 5deg latitude-longitude regions over the global oceans (after removing cases in which significant meteorological differences are found between the low and high aerosol populations), results are qualitatively similar to those off the coast of Africa.

Published
2008

47. Black Carbon Concentration from Worldwide Aerosol Robotic Network (AERONET) Measurements

Author

Schuster, Gregory L, Dubovik, Oleg, Holben, Brent N, and Clothiaux, Eugene E

Subjects
Environment Pollution
Abstract

The carbon emissions inventories used to initialize transport models and general circulation models are highly parameterized, and created on the basis of multiple sparse datasets (such as fuel use inventories and emission factors). The resulting inventories are uncertain by at least a factor of 2, and this uncertainty is carried forward to the model output. [Bond et al., 1998, Bond et al., 2004, Cooke et al., 1999, Streets et al., 2001] Worldwide black carbon concentration measurements are needed to assess the efficacy of the carbon emissions inventory and transport model output on a continuous basis.

Published
2006

48. Offshore Radiation Observations for Climate Research at the CERES Ocean Validation Experiment

Author

Rutledge, Charles K, Schuster, Gregory L, Charlock, Thomas P, Denn, Frederick M, Smith, William L., Jr, Fabbri, Bryan E, Madigan, James J., Jr, and Knapp, Robert J

Subjects
Meteorology And Climatology
Abstract

When radiometers on a satellite are pointed towards the planet with the goal of understanding a phenomenon quantitatively, rather than just creating a pleasing image, the task at hand is often problematic. The signal at the detector can be affected by scattering, absorption, and emission; and these can be due to atmospheric constituents (gases, clouds, and aerosols), the earth's surface, and subsurface features. When targeting surface phenomena, the remote sensing algorithm needs to account for the radiation associated with the atmospheric constituents. Likewise, one needs to correct for the radiation leaving the surface, when atmospheric phenomena are of interest. Rigorous validation of such remote sensing products is a real challenge. In visible and near infrared wavelengths, the jumble of effects on atmospheric radiation are best accomplished over dark surfaces with fairly uniform reflective properties (spatial homogeneity) in the satellite instrument's field of view (FOV). The ocean's surface meets this criteria; land surfaces - which are brighter, more spatially inhomogeneous, and more changeable with time - generally do not. NASA's Clouds and the Earth's Radiant Energy System (CERES) project has used this backdrop to establish a radiation monitoring site in Virginia's coastal Atlantic Ocean. The project, called the CERES Ocean Validation Experiment (COVE), is located on a rigid ocean platform allowing the accurate measurement of radiation parameters that require precise leveling and pointing unavailable from ships or buoys. The COVE site is an optimal location for verifying radiative transfer models and remote sensing algorithms used in climate research; because of the platform's small size, there are no island wake effects; and suites of sensors can be simultaneously trained both on the sky and directly on ocean itself. This paper describes the site, the types of measurements made, multiple years of atmospheric and ocean surface radiation observations, and satellite validation results.

Published
2006

50. The Angstrom Exponent and Bimodal Aerosol Size Distributions

Author

Schuster, Gregory L, Dubovik, Oleg, and Holben, Brent H

Subjects
Geophysics
Abstract

Powerlaws have long been used to describe the spectral dependence of aerosol extinction, and the wavelength exponent of the aerosol extinction powerlaw is commonly referred to as the Angstrom exponent. The Angstrom exponent is often used as a qualitative indicator of aerosol particle size, with values greater than two indicating small particles associated with combustion byproducts, and values less than one indicating large particles like sea salt and dust. In this study, we investigate the relationship between the Angstrom exponent and the mode parameters of bimodal aerosol size distributions using Mie theory calculations and Aerosol Robotic Network (AERONET) retrievals. We find that Angstrom exponents based upon seven wavelengths (0.34, 0.38, 0.44, 0.5, 0.67, 0.87, and 1.02 micrometers) are sensitive to the volume fraction of aerosols with radii less then 0.6 micrometers, but not to the fine mode effective radius. The Angstrom exponent is also known to vary with wavelength, which is commonly referred to as curvature; we show how the spectral curvature can provide additional information about aerosol size distributions for intermediate values of the Angstrom exponent. Curvature also has a significant effect on the conclusions that can be drawn about two-wavelength Angstrom exponents; long wavelengths (0.67, 0.87 micrometers) are sensitive to fine mode volume fraction of aerosols but not fine mode effective radius, while short wavelengths (0.38, 0.44 micrometers) are sensitive to the fine mode effective radius but not the fine mode volume fraction.

Published
2005

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