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Author: Sara Lance
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages :
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Book Description
It has been historically assumed that most of the uncertainty associated with the aerosol indirect effect on climate can be attributed to the unpredictability of updrafts. We assess the sensitivity of cloud droplet number density to realistic variations in aerosol chemical properties and to variable updraft velocities using a 1-dimensional cloud parcel model. The results suggest that aerosol chemical variability may be as important to the aerosol indirect effect as the effect of unresolved cloud dynamics, especially in polluted environments. We next used a continuous flow streamwise thermal gradient Cloud Condesnation Nuclei counter (CCNc) to study the water-uptake properties of the ambient aerosol, by exposing an aerosol sample to a controlled water vapor supersaturation and counting the resulting number of droplets. The heat transfer properties and droplet growth within the CCNc were first modeled and experimentally characterized. We describe results from the MIRAGE field campaign at a ground-based site during March, 2006. Size-resolved CCN activation spectra and hygroscopic growth factor distributions of the ambient aerosol in Mexico City were obtained, and an analytical technique was developed to quantify a probability distribution of solute volume fractions for the CCN, as well as the aerosol mixing-state. The CCN were shown to be much less CCN active than ammonium sulfate, with water uptake properties more consistent with low molecular weight organic compounds. We also describe results from the GoMACCS field study, an airborne field campaign in Houston, Texas during August-September, 2006. GoMACCS tested our ability to predict CCN for highly polluted conditions with limited chemical information. Assuming the particles were composed purely of ammonium sulfate, CCN closure was obtained with a 10% overprediction bias on average for CCN concentrations ranging from less than 100 cm-3 to over 10,000 cm-3, but with on average 50% variability. Assuming measured concentrations of organics to be internally mixed and insoluble tended to reduce the overprediction bias for less polluted conditions, but led to underprediction bias in the most polluted conditions. Comparing the two campaigns, it is clear that the chemistry of the particles plays an important role in our ability to predict CCN concentrations.
Author: Sara Lance
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages :
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Book Description
It has been historically assumed that most of the uncertainty associated with the aerosol indirect effect on climate can be attributed to the unpredictability of updrafts. We assess the sensitivity of cloud droplet number density to realistic variations in aerosol chemical properties and to variable updraft velocities using a 1-dimensional cloud parcel model. The results suggest that aerosol chemical variability may be as important to the aerosol indirect effect as the effect of unresolved cloud dynamics, especially in polluted environments. We next used a continuous flow streamwise thermal gradient Cloud Condesnation Nuclei counter (CCNc) to study the water-uptake properties of the ambient aerosol, by exposing an aerosol sample to a controlled water vapor supersaturation and counting the resulting number of droplets. The heat transfer properties and droplet growth within the CCNc were first modeled and experimentally characterized. We describe results from the MIRAGE field campaign at a ground-based site during March, 2006. Size-resolved CCN activation spectra and hygroscopic growth factor distributions of the ambient aerosol in Mexico City were obtained, and an analytical technique was developed to quantify a probability distribution of solute volume fractions for the CCN, as well as the aerosol mixing-state. The CCN were shown to be much less CCN active than ammonium sulfate, with water uptake properties more consistent with low molecular weight organic compounds. We also describe results from the GoMACCS field study, an airborne field campaign in Houston, Texas during August-September, 2006. GoMACCS tested our ability to predict CCN for highly polluted conditions with limited chemical information. Assuming the particles were composed purely of ammonium sulfate, CCN closure was obtained with a 10% overprediction bias on average for CCN concentrations ranging from less than 100 cm-3 to over 10,000 cm-3, but with on average 50% variability. Assuming measured concentrations of organics to be internally mixed and insoluble tended to reduce the overprediction bias for less polluted conditions, but led to underprediction bias in the most polluted conditions. Comparing the two campaigns, it is clear that the chemistry of the particles plays an important role in our ability to predict CCN concentrations.
Author: Wiesje Mooiweer
Publisher: ProQuest
ISBN: 9781109180466
Category : Atmospheric aerosols
Languages : en
Pages : 182
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Book Description
Particulates that form the atmospheric aerosol play a significant role in determining Earth's climate, both directly through scattering and absorption of solar radiation, and indirectly by impacting cloud formation processes. They are present in a large range of sizes, concentrations, chemical compositions, and compositional inhomogeneities, complicating our ability to quantify the aerosol's direct and indirect effects. This work investigates the dependence of aerosol light scattering on relative humidity (RH) and chemical composition, and the effect of organic material on scattering enhancement and implied particle growth characteristics. It utilizes measurements carried out in the Elk Mountain/Laramie Aerosol Characterization Experiment (EMLACE), in which observations were made at both a clean high-altitude mid-continental site (Elk Mountain, WY) in summer (2006), and in a small urban environment (Laramie, WY) during both summer (2005) and winter (2006). High time resolution measurements of scattering extinction from both dry and humidified PM 1 aerosols were obtained together with time resolved measurements of PM 1 volatile aerosol chemical composition and mass loading. Variabilities in particle chemical composition and optical behavior with location and season are documented. Scattering extinction is positively correlated with aerosol mass loading. Enhanced scattering, due to water uptake by the particles at high RH, is described by a scattering enhancement factor (f(RH)), which is found to be smaller with increasing mass fraction of organic material. Observed f(RH) values are interpreted in terms of mass weighted contributions (f(RH high) Inorg and f(RH high) Org) from the particulate inorganic and organic material at high RH. Analyses show that whereas f(RH high) Inorg varies continually, depending on the physical and chemical properties of the aerosol, the experimental data can, in general, be adequately interpreted using a value of 1.0 for f(RH high) Org (though values up to 1.1 are occasionally indicated), suggesting that organic material does not significantly promote increased scattering at high RH. Numerical values of f(RH high) Inorg and f(RH high) Org were used to develop an empirical parameterization of changes in aerosol optical properties with increasing RH, based solely on variations in particulate chemical composition. This parameterization successfully reconstructs variations in f(RH) for the observed ambient aerosols over the entire range of RH values employed in the experiments.
Author: Xueying Qin
Publisher:
ISBN:
Category :
Languages : en
Pages : 353
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Book Description
Aerosols are solid or liquid particles suspended in the air. They are generated from a range of natural and anthropogenic sources. Aerosols also experience various reactions such as photo-oxidation and aqueous-phase processing, which constantly change their physical and chemical properties. Therefore, in order to determine the emission inventory, it is important to study aerosol reactions and transformation mechanisms in ambient atmosphere. The research described in this dissertation aimed to characterize temporal, spatial, and seasonal variations on ambient aerosol chemical compositions and formation mechanisms. The results contribute to the understanding of air pollution, climate change, and human health problems, and to devising necessary strategies and policies to resolve these problems.
Author: Jessie Marie Creamean
Publisher:
ISBN: 9781267646668
Category :
Languages : en
Pages : 236
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Book Description
Atmospheric aerosols have significant implications for human health and climate. For instance, aerosols impact climate directly by scattering and absorbing solar and terrestrial radiation and indirectly by acting as cloud condensation nuclei (CCN) and ice nuclei (IN), which facilitate cloud droplet and ice crystal formation, respectively. Changes in chemistry, size, and number concentrations between different locations and over time alter how aerosols impact air quality and cloud formation, and can have broader implications on precipitation efficiency and phase. Further, aerosol composition largely depends on meteorology, which influences sources and chemical transformation in the atmosphere. Aerosol-cloud-precipitation interactions represent one of the largest sources of uncertainty in climate science; therefore, a better understanding of the aerosols that contribute to these effects is needed. To address this source of uncertainty, the chemical composition of individual ambient aerosols and aerosols as insoluble residues in precipitation samples was determined using aerosol time-of-flight mass spectrometry (ATOFMS) and provided insight into their potential to serve as cloud seeds at three different locations over time. A three-year summer study (2005-2007) in Riverside, CA afforded information on the inter-annual variability of the urban aerosol due to changes in aerosol transport and meteorological conditions. In the summer of 2008 in Atlanta, GA, tropical cyclones shifted the representative aged urban aerosol to a less-aged, less-CCN active aerosol population, having implications on regional cloud formation after extreme weather events. At a remote site in the Sierra Nevada Mountains in the winter of 2009, observations of newly-formed aerosols presented a new source of CCN. Inter-annual trends in precipitation at the same remote site showed how IN transported from the Sahara and Asia potentially influenced precipitation processes during three winter seasons (2009-2011). Investigating changes in cloud seeds represents a longer-term goal to reduce uncertainties associated with modeling aerosol-cloud-precipitation interactions. Larger spatial and temporal coverage is needed to better understand trends in cloud formation and precipitation and to provide more detail for regional and global model parameterization. The results presented herein represent a noteworthy advancement towards understanding variation in composition and sources of cloud seeds in different regions and in most cases long time periods.
Author: Beth Friedman
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 151
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Book Description
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: J. E. Penner
Publisher:
ISBN:
Category : Aerosol propellants
Languages : en
Pages : 68
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Book Description
Author: Kirill Ya. Kondratyev
Publisher: Springer Science & Business Media
ISBN: 3540376984
Category : Science
Languages : en
Pages : 595
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Book Description
This book provides the first comprehensive analysis of how aerosols form in the atmosphere through in situ processes as well as via transport from the surface (dust storms, seas spray, biogenic emissions, forest fires etc.). Such an analysis has been followed by the consideration of both observation data (various field observational experiments) and numerical modeling results to assess climate impacts of aerosols bearing in mind that these impacts are the most significant uncertainty in studying natural and anthropogenic causes of climate change.
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: Luz Teresa Padro Martinez
Publisher:
ISBN:
Category : Atmospheric aerosols
Languages : en
Pages :
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Book Description
It is well known that atmospheric aerosols provide the sites for forming cloud droplets, and can affect the Earth's radiation budget through their interactions with clouds. The ability of aerosols to act as cloud condensation nuclei is a strong function of their chemical composition and size. The compositional complexity of aerosol prohibits their explicit treatment in atmospheric models of aerosol-cloud interactions. Nevertheless, the cumulative impact of organics on CCN activity is still required, as carbonaceous material can constitute up to 90% of the total aerosol, 10-70% of which is water soluble. Therefore it is necessary to characterize the water soluble organic carbon fraction by CCN activation, droplet growth kinetics, and surface tension measurements. In this thesis, we investigate the water soluble properties, such as surface tension, solubility, and molecular weight, of laboratory and ambient aerosols and their effect on CCN formation. A mechanism called Curvature Enhanced Solubility is proposed and shown to explain the apparent increased solubility of organics. A new method, called Köhler Theory Analysis, which is completely new, fast, and uses minimal amount of sample was developed to infer the molar volume (or molar mass) of organics. Due to the success of the technique in predicting the molar volume of laboratory samples, it was applied to aerosols collected in Mexico City. Additionally the surface tension, CCN activity, and droplet growth kinetics of these urban polluted aerosols were investigated. Studies performed for the water soluble components showed that the aerosols in Mexico City have surfactants present, can readily become CCN, and have growth similar to ammonium sulfate. Finally, aerosols from three different polluted sources, urban, bovine, and ship emissions, were collected and characterized. The data assembled was used to predict CCN concentrations and access our understanding of the system. From these analyses, it was evident that knowledge of the chemical composition and mixing state of the aerosol is necessary to achieve agreement between observations and predictions. The data obtained in this thesis can be introduced and used as constraints in aerosol-cloud interaction parameterizations developed for global climate models, which could lead to improvements in the indirect effect of aerosols.
Author: Peter Knippertz
Publisher: Springer
ISBN: 9401789789
Category : Science
Languages : en
Pages : 526
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Book Description
This volume presents state-of-the-art research about mineral dust, including results from field campaigns, satellite observations, laboratory studies, computer modelling and theoretical studies. Dust research is a new, dynamic and fast-growing area of science and due to its multiple roles in the Earth system, dust has become a fascinating topic for many scientific disciplines. Aspects of dust research covered in this book reach from timescales of minutes (as with dust devils, cloud processes and radiation) to millennia (as with loess formation and oceanic sediments), making dust both a player and recorder of environmental change. The book is structured in four main parts that explore characteristics of dust, the global dust cycle, impacts of dust on the Earth system, and dust as a climate indicator. The chapters in these parts provide a comprehensive, detailed overview of this highly interdisciplinary subject. The contributions presented here cover dust from source to sink and describe all the processes dust particles undergo while travelling through the atmosphere. Chapters explore how dust is lifted and transported, how it affects radiation, clouds, regional circulations, precipitation and chemical processes in the atmosphere and how it deteriorates air quality. The book explores how dust is removed from the atmosphere by gravitational settling, turbulence or precipitation, how iron contained in dust fertilizes terrestrial and marine ecosystems, and about the role that dust plays in human health. We learn how dust is observed, simulated using computer models and forecast. The book also details the role of dust deposits for climate reconstructions. Scientific observations and results are presented, along with numerous illustrations. This work has an interdisciplinary appeal and will engage scholars in geology, geography, chemistry, meteorology and physics, amongst others with an interest in the Earth system and environmental change. body>
