Cloud Scavenging Effects on Aerosol Radiative and Cloud-nucleating Properties - Final Technical Report PDF Download

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Languages : en
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The optical properties of aerosol particles are the controlling factors in determining direct aerosol radiative forcing. These optical properties depend on the chemical composition and size distribution of the aerosol particles, which can change due to various processes during the particles' lifetime in the atmosphere. Over the course of this project we have studied how cloud processing of atmospheric aerosol changes the aerosol optical properties. A counterflow virtual impactor was used to separate cloud drops from interstitial aerosol and parallel aerosol systems were used to measure the optical properties of the interstitial and cloud-scavenged aerosol. Specifically, aerosol light scattering, back-scattering and absorption were measured and used to derive radiatively significant parameters such as aerosol single scattering albedo and backscatter fraction for cloud-scavenged and interstitial aerosol. This data allows us to demonstrate that the radiative properties of cloud-processed aerosol can be quite different than pre-cloud aerosol. These differences can be used to improve the parameterization of aerosol forcing in climate models.

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Languages : en
Pages : 996

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Book Description
The optical properties of aerosol particles are the controlling factors in determining direct aerosol radiative forcing. These optical properties depend on the chemical composition and size distribution of the aerosol particles, which can change due to various processes during the particles' lifetime in the atmosphere. Over the course of this project we have studied how cloud processing of atmospheric aerosol changes the aerosol optical properties. A counterflow virtual impactor was used to separate cloud drops from interstitial aerosol and parallel aerosol systems were used to measure the optical properties of the interstitial and cloud-scavenged aerosol. Specifically, aerosol light scattering, back-scattering and absorption were measured and used to derive radiatively significant parameters such as aerosol single scattering albedo and backscatter fraction for cloud-scavenged and interstitial aerosol. This data allows us to demonstrate that the radiative properties of cloud-processed aerosol can be quite different than pre-cloud aerosol. These differences can be used to improve the parameterization of aerosol forcing in climate models.

Author: Constantin Andronache
Publisher: Elsevier
ISBN: 012810550X
Category : Science
Languages : en
Pages : 302

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Mixed-Phase Clouds: Observations and Modeling presents advanced research topics on mixed-phase clouds. As the societal impacts of extreme weather and its forecasting grow, there is a continuous need to refine atmospheric observations, techniques and numerical models. Understanding the role of clouds in the atmosphere is increasingly vital for current applications, such as prediction and prevention of aircraft icing, weather modification, and the assessment of the effects of cloud phase partition in climate models. This book provides the essential information needed to address these problems with a focus on current observations, simulations and applications. Provides in-depth knowledge and simulation of mixed-phase clouds over many regions of Earth, explaining their role in weather and climate Features current research examples and case studies, including those on advanced research methods from authors with experience in both academia and the industry Discusses the latest advances in this subject area, providing the reader with access to best practices for remote sensing and numerical modeling

Author: Panel on Aerosol Radiative Forcing and Climate Change
Publisher: National Academies Press
ISBN: 0309588871
Category : Science
Languages : en
Pages : 180

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This book recommends the initiation of an "integrated" research program to study the role of aerosols in the predicted global climate change. Current understanding suggest that, even now, aerosols, primarily from anthropogenic sources, may be reducing the rate of warming caused by greenhouse gas emissions. In addition to specific research recommendations, this book forcefully argues for two kinds of research program integration: integration of the individual laboratory, field, and theoretical research activities and an integrated management structure that involves all of the concerned federal agencies.

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Languages : en
Pages : 11

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Anthropogenic aerosols influence the earth's radiation balance and climate directly, by scattering shortwave (solar) radiation in cloud-free conditions and indirectly, by increasing concentrations of cloud droplets thereby enhancing cloud shortwave reflectivity. These effects are thought to be significant in the context of changes in the earth radiation budget over the industrial period, exerting a radiative forcing that is of comparable magnitude to that of increased concentrations of greenhouse gases over this period but opposite in sign. However the magnitudes of both the direct and indirect aerosol effects are quite uncertain. Much of the uncertainty of the indirect effect arises from incomplete ability to describe changes in cloud properties arising from anthropogenic aerosols. This paper examines recent studies pertaining to the influence of anthropogenic aerosols on loading and properties of aerosols affecting their cloud nucleating properties and indicative of substantial anthropogenic influence on aerosol and cloud properties over the North Atlantic.

Author: Beth Friedman
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 151

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Aerosol-cloud interactions represent a significant uncertainty with respect to radiative forcing and future climate change. Both particle composition and size play key, yet poorly understood, roles in determining the cloud nucleating capabilities of aerosols. The following describes ambient and laboratory measurements of cloud condensation nuclei (CCN) and ice nuclei (IN) measurements from a variety of sources, with the goal of understanding how composition and size interact in forming cloud droplets and ice crystals and the potential importance of aerosol composition and atmospheric aging processes on constraining uncertainties associated with the cloud nucleating properties of aerosols. Motivated by the anthropogenic emissions of soot particles as well as the potential properties of aged soot particles, ice formation and droplet activation of soot particles of various size and composition were studied. Generated soot particles were coated with a variety of atmospherically relevant acids of varying solubility properties. The particles were also exposed to ozone in order to simulate atmospheric oxidation and aging. A custom-built ice chamber was utilized to show that both uncoated and coated soot particles comparable to those generated in our studies are unlikely to significantly contribute to the global budget of heterogeneous IN at relevant atmospheric temperatures. This result is emphasized by comparison to an efficient ice nucleus, such as mineral dust. Coatings and oxidation by ozone also did not significantly alter the ice nucleation behavior of soot particles but aided in the uptake of water, suggesting the altered composition of a hydrophobic particle is important to take into account for cloud droplet activation. To assess the importance of particle composition in cloud droplet activation, measurements of CCN concentrations, single particle composition, and number size distributions were conducted at a high-elevation research site. The temporal evolution of detailed single particle chemical composition was compared with changes in CCN activation. A variety of particle types were observed; CCN activation largely followed the behavior of the sulfate-containing particle types; biomass burning particles also contained hygroscopic material that impacted CCN activation. The observed particles were largely aged; few local sources contributed to the particle composition due to the high elevation of the site. The results were also interpreted in terms of the assumed hygroscopicity of free tropospheric aerosol. As a further examination of the impacts of aging processes on aerosol hygroscopicity measurements of CCN concentrations, aerosol composition, and number size distributions were conducted during the winter season from of a variety of air masses, including aged marine, continental, and urban sources. Based on the measured chemistry and size properties of the ambient aerosol, CCN concentrations were predicted in order to assess the amount of composition detail necessary to explain droplet activation. Direct measurements of the composition of the activated droplets were also conducted with a novel technique to separate activated droplets from un-activated aerosol. Results suggest the importance of inorganic species in droplet activation, with non-oxidized organic species having negligible impacts on total aerosol hygroscopicity. Using the same novel separation technique, measurements of the single particle composition of activated droplet residual particles were determined at an urban site in the summertime, with similar air mass trajectories as the previous wintertime site, as well as influence from local urban aerosol sources. As a function of atmospheric supersaturation conditions the composition of activated droplet residual particles was compared to the ambient aerosol composition. The study was utilized to determine the level of composition and size detail required to describe droplet activation at a site with similar aged air mass trajectories to the previous study.

Author:
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ISBN:
Category :
Languages : en
Pages : 20

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Clouds play an important role in weather and climate. In addition to their key role in the hydrologic cycle, clouds scatter incoming solar radiation and trap infrared radiation from the surface and lower atmosphere. Despite their importance, feedbacks involving clouds remain as one of the largest sources of uncertainty in climate models. To better simulate cloud processes requires better characterization of cloud microphysical processes, which can affect the spatial extent, optical depth and lifetime of clouds. To this end, we developed a new parameterization to be used in numerical models that describes the variation of ice nuclei (IN) number concentrations active to form ice crystals in mixed-phase (water droplets and ice crystals co-existing) cloud conditions as these depend on existing aerosol properties and temperature. The parameterization is based on data collected using the Colorado State University continuous flow diffusion chamber in aircraft and ground-based campaigns over a 14-year period, including data from the DOE-supported Mixed-Phase Arctic Cloud Experiment. The resulting relationship is shown to more accurately represent the variability of ice nuclei distributions in the atmosphere compared to currently used parameterizations based on temperature alone. When implemented in one global climate model, the new parameterization predicted more realistic annually averaged cloud water and ice distributions, and cloud radiative properties, especially for sensitive higher latitude mixed-phase cloud regions. As a test of the new global IN scheme, it was compared to independent data collected during the 2008 DOE-sponsored Indirect and Semi-Direct Aerosol Campaign (ISDAC). Good agreement with this new data set suggests the broad applicability of the new scheme for describing general (non-chemically specific) aerosol influences on IN number concentrations feeding mixed-phase Arctic stratus clouds. Finally, the parameterization was implemented into a regional cloud-resolving model to compare predictions of ice crystal concentrations and other cloud properties to those observed in two intensive case studies of Arctic stratus during ISDAC. Our implementation included development of a prognostic scheme of ice activation using the IN parameterization so that the most realistic treatment of ice nuclei, including their budget (gains and losses), was achieved. Many cloud microphysical properties and cloud persistence were faithfully reproduced, despite a tendency to under-predict (by a few to several times) ice crystal number concentrations and cloud ice mass, in agreement with some other studies. This work serves generally as the basis for improving predictive schemes for cloud ice crystal activation in cloud and climate models, and more specifically as the basis for such a scheme to be used in a Multi-scale Modeling Format (MMF) that utilizes a connected system of cloud-resolving models on a global grid in an effort to better resolve cloud processes and their influence on climate.

Author:
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ISBN:
Category :
Languages : en
Pages : 10

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The formation of clouds is an essential element in understanding the Earth's radiative budget. Liquid water clouds form when the relative humidity exceeds saturation and condensedphase water nucleates on atmospheric particulate matter. The effect of aerosol properties such as size, morphology, and composition on cloud droplet formation has been studied theoretically as well as in the laboratory and field. Almost without exception these studies have been limited to parallel measurements of aerosol properties and cloud formation or collection of material after the cloud has formed, at which point nucleation information has been lost. Studies of this sort are adequate when a large fraction of the aerosol activates, but correlations and resulting model parameterizations are much more uncertain at lower supersaturations and activated fractions.

Author: Zev Levin
Publisher: Springer Science & Business Media
ISBN: 1402086903
Category : Science
Languages : en
Pages : 399

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Book Description
Life on Earth is critically dependent upon the continuous cycling of water between oceans, continents and the atmosphere. Precipitation (including rain, snow, and hail) is the primary mechanism for transporting water from the atmosphere back to the Earth’s surface. It is also the key physical process that links aspects of climate, weather, and the global hydrological cycle. Changes in precipitation regimes and the frequency of extreme weather events, such as floods, droughts, severe ice/snow storms, monsoon fluctuations and hurricanes are of great potential importance to life on the planet. One of the factors that could contribute to precipitation modification is aerosol pollution from various sources such as urban air pollution and biomass burning. Natural and anthropogenic changes in atmospheric aerosols might have important implications for precipitation by influencing the hydrological cycle, which in turn could feed back to climate changes. From an Earth Science perspective, a key question is how changes expected in climate will translate into changes in the hydrological cycle, and what trends may be expected in the future. We require a much better understanding and hence predictive capability of the moisture and energy storages and exchanges among the Earth’s atmosphere, oceans, continents and biological systems. This book is a review of our knowledge of the relationship between aerosols and precipitation reaching the Earth's surface and it includes a list of recommendations that could help to advance our knowledge in this area.

Author: Stefano Guerzoni
Publisher: Springer Science & Business Media
ISBN: 0792342941
Category : Science
Languages : en
Pages : 415

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The atmosphere is an important pathway for the transport of continentally-derived material to the oceans. In this respect the Mediterranean Sea is of special importance because its atmosphere receives inputs of anthropogenic aerosols from the north and desert- derived Saharan dusts from the south. The dusts, much of which is transported in the form of seasonal `pulses', have important effects on climate, marine chemistry and sedimentation in the Mediterranean Sea. This volume brings together reviews and specific-topic papers on the following aspects of Saharan dust transport to the Mediterranean Sea: (i) the modelling of Saharan dust transport, (ii) the chemistry and mineralogy of the dusts and their effect on precipitation, (iii) the contribution of the dusts to marine sedimentation, (iv) the aerobiology of the dusts, and (v) climatic implications of Saharan dust transport. The volume is aimed at students and researchers with an interest in the climate, biogeochemistry and geology of the Mediterranean Sea.