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Atmospheric Science Papers (Blue Books)

Permanent URI for this collectionhttps://hdl.handle.net/10217/100334

Much of this digital collection of Blue Books comes from CSU's Department of Atmospheric Science. Included are student theses and dissertations and project reports dating from 1959 to 2007. The works focus on different areas of atmospheric science research such as climate change, severe weather, climatology, solar radiation, remote sensing, wind forecasting, and air quality.

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Browsing Atmospheric Science Papers (Blue Books) by Subject "Aerosols -- Environmental aspects"

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    Cloud processing of aerosol using a hybrid LES/parcel model with solute-following microphysics
    (Colorado State University. Libraries, 1995-08) Richardson, Wendy A., author; Kreidenweis, Sonia M., author; Cotton, William R., author
    The importance of climate forcings due to direct and indirect aerosol influences have been theorized, observed, and modeled, and are accepted on a qualitative level. Though these effects have been identified, the magnitude of their effect locally and globally has been difficult to estimate. Enhancement of the existing Regional Atmospheric Modeling System (RAMS) developed at CSU provides a way to investigate these impacts. The RAMS explicit microphysics has been expanded to include both an aerosol distribution stored in 14 size categories and separate solute mass and concentration information for each water drop size category. The initial aerosol distribution is activated according to chemical and physical principles; that is, it is not some parameterized function. The aerosol is subsequently followed as solute in each water bin, where each droplet size category independently stores a solute concentration. Because the aerosol mass is followed as solute in the drops, information on the changes in aerosol size and number due to cloud processing of an evaporating cloud is available. Schemes for bin representation, aerosol activation, solute transfer during droplet growth, and aerosol regeneration from evaporating droplets were tested in a standalone box model. To determine the effectiveness of using the expanded microphysics in a full scale LES model, a series of tests using a RAMS simulation of a two dimensional hill cap cloud were performed. A hybrid LES/parcel model was also developed. Several passive tracer trajectory environmental profiles through the hill cap cloud were determined during the full RAMS simulation. These profiles were used to drive a parcel model having the same explicit microphysics as the full RAMS simulation. Additionally, the hybrid LES/parcel model was used to drive parcels derived from a RAMS simulation of the same cloud with bulk microphysics. Direct comparisons of aerosol and droplet distributions in time and space were made for the full LES model and for the hybrid LES/parcel simulations. The hybrid LES/parcel model shows promise in its ability to combine very dynamically complex cloud types with complex cloud microphysics and chemistry. Cloud microphysical features, such as cloud base supersaturation maximum, were not well represented in the RAMS simulation, but were in the parcel model simulations. Aerosol which have deliquesced and/or activated to cloud droplets serve as sites for aqueous chemical reactions which can enhance the aerosol mass. An aqueous chemistry module (Kreidenweis, 1992), appropriate for use as a stand-alone model, has been extended. The expanded version can be used to represent both externally and internally mixed aerosol. A seasalt aerosol option is included which can be used to represent marine aerosol distributions. Seasalt constituents that directly affect the chemistry are represented explicitly, along with a parameterization for seasalt alkalinity. Options for multiple droplet sizes and concurrent droplet growth have been created, for incorporation into a dynamical/microphysical cloud model.
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    Preliminary results from a two-moment aerosol model applied to a three-dimensional model of the global sulfur cycle
    (Colorado State University. Libraries, 1995-12) Kreidenweis, Sondra M., author; Harrington, Debra Y., author; Walton, John J., author; Penner, Joyce E., author
    The focus of this work is the development and application of a two-mode, two-moment model of sulfate aerosol dynamics that is coupled to the Lawrence Livermore National Laboratory (LLNL) three dimensional transport, transformation, and deposition model, GRANTOUR. The new aerosol model predicts two moments of the distribution, particle number concentration and particle mass concentration; earlier studies of the global sulfur cycle have predicted only a single moment of the aerosol, the total mass of particulate sulfate. Two modes are used to represent the fine aerosol fraction in this study. The treatment of sulfuric acid vapor is also modified from earlier studies, from a diagnostic variable usually set equal to zero, to a prognostic variable which drives the gas-to-particle conversion in the aerosol model. The parameterized two-moment aerosol model was developed for computational efficiency and the small number of prognostic variables, which reduce storage requirements in the large-scale model. The addition of this simple aerosol scheme nearly tripled the computational time needed to complete a month of simulation, relative to that for a chemistry-only run. The implementation of the aerosol model in GRANTO UR is described, and preliminary steady-state results from perpetual July simulations are presented and discussed. Anthropogenic and natural sources of sulfur gases were used as input, with simple oxidation schemes converting the gases to sulfuric acid. No direct emissions of particulate matter or other sources of aerosol mass were considered. Predictions of aerosol sulfate mass concentrations at the surface are nearly identical to previous results from the single moment aerosol scheme, and are highest in industrialized regions with large anthropogenic emissions. However, the spatial distribution of number concentration is markedly different from that for the particulate mass. In particular, the predicted monthly mean surface number concentrations in continental regions are much lower than observations. This result is interpreted as indicating that direct emissions of particulate matter are the strongest regulator of particle number concentration in such regions, and must be included to improve comparisons with observations. At 355 mb, however, the predicted number concentrations are generally higher than those at the surface, and show a latitudinally banded structure similar to some observations. This result is interpreted as signifying a lessening of the importance of surf ace primary emissions in determining the number concentrations of free tropospheric aerosol. A trajectory analysis is performed for one parcel which was lifted to a 300 mb height after picking up emissions in the marine boundary layer of the western North Atlantic. Several thousand particles cm3 were nucleated in this parcel in the free troposphere. It was later brought to the surface in subsiding air over northern Africa, where it contributed to an unexpectedly high monthly mean number concentration in this region. The analysis, although limited in scope, supports the idea that the free troposphere may serve as a source of aerosol number to the boundary layer.
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    Studies of ice formation behaviors of upper tropospheric aerosol and their chemical compositions by continuous flow thermal diffusion chamber
    (Colorado State University. Libraries, 1999-10) Chen, Yalei, author
    Studies were conducted to investigate ice formation by aerosol particles at upper tropospheric conditions. The continuous flow thermal diffusion chamber ( CFD) was used in both field and lab experiments to determine the conditions for the onset of ice formation in ambient and lab aerosols. After confirming the capability of the CFD to separate ice nucleating particles (IN) from non-IN, we collected samples of both IN and non-IN from the upper troposphere (UT) and the lower stratosphere during the 1996 NASA SUCCESS airborne field campaign. The chemical compositions of these particles were measured by electron microscopy, an individual particle analysis technique. From these results, as well as previous studies, ammoniated sulfates, sulfuric acid, and soot particles with different coatings were selected as representative UT aerosols for further laboratory investigation of their ice formation behaviors. In controlled laboratory studies, the phase states of (NH4)2SO4 and NH4HSO4 particles were found to have important impacts on their ice formation capabilities. Dry (NH4)2SO4 particles nucleated ice only at high relative humidity with respect to water at temperatures between -40°C and -60°C. Ammonium sulfate particles that entered the diffusion chamber in a liquid state froze by homogenous freezing at relative humidities that were 10% lower than where ice nucleated on dry particles. Likewise, crystalline or partially crystallized (as letovicite) NH4HSO 4 particles required higher relative humidities for ice nucleation than did initially liquid bisulfate particles . Based on our observations, 0.2 μm particles composed of either ammonium sulfate or bisulfate in a liquid solution freeze at lower RH at UT temperatures than do 0.05 μm sulfuric acid aerosol particles. The results indicate that, for liquid droplets, the size effect may be more important than the degree of ammoniation of the sulfate compound. Soot particles with different coating treatments were investigated in a similar manner as the sulfates. Submicron particles of commercial soot were coated with H2S04 in amounts of zero to several percent by weight. Untreated soot particles showed activity as deposition/sorption ice nuclei; and soot particles with approximately one monolayer equivalent coating of sulfuric acid froze at humidities slightly higher than those of untreated soot. These observations suggest that dilution of sulfuric acid was required before homogeneous freezing. Heterogeneous freezing was observed on particles with multilayer coverage at cold temperatures (< -53°C). We also generated soot particles by combustion of jet fuels and examined the freezing behavior of 0.05 μm monodisperse particles. The jet fuel soot particles contain about 10% by weight soluble matter, and did not freeze below 95% RH. Similarities existed in the ice formation behaviors of these jet fuel soot particles and 0.016 μm pure sulfuric acid particles. These laboratory results suggest that small solution droplets, with diameters of several hundredths of microns, require relatively high humidity to freeze homogeneously, and are therefore unlikely to be the particles that form cirrus clouds with continental origins. Dry crystals of sulfate form ice near water saturation. Sulfuric acid coating changes the ice formation properties of soot particles dramatically. With multilayer sulfuric acid coating, soot particles initiate homogeneous freezing at cirrus cloud conditions at cold temperatures. This suggests a heterogeneous nucleation pathway for continental cirrus formation. Pure soot particles and those with a small amount of sulfuric acid coating, like fresh aircraft exhaust, only form contrails near water saturation.
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    Studies of the relationship between submicron marine aerosol and initial marine stratus properties
    (Colorado State University. Libraries, 1993-12) Jensen-Leute, Tara L., author; Kreidenweis, Sonia M., author
    A systematic study of the relationship between submicron aerosols and the marine stratus cloud properties has been undertaken. The first part of the study included participation in the Atlantic Stratocumulus Transition Experiment - Marine Aerosol and Gas Exchange (ASTEX/MAGE) cooperative research experiment Measurements of submicron marine aerosol were collected using the Differential Mobility Particle Sizing (DMSP) system for determining the typical chemical composition and aerosol size distribution of marine aerosol. The second part of the investigation involved cloud process simulation with the Colorado State University dynamic cloud chamber. Marine aerosol distribution measurements were taken over a 25 day period from June 1 to June 25, 1992. Analysis of the data showed that the distributions were generally bimodal in clean air masses with total number concentrations ranging from 100 to 900 particles cm-3, while distributions were generally monomodal in polluted air masses with total number concentrations ranging from 800 to 1400 particles cm-3. Using the '"typical" thermodynamic and aerosol characteristics observed during the field project, the Colorado State University dynamic cloud chamber was used to conduct a well controlled study of the effects of submicron aerosol on the formation of marine stratus type clouds. Selected size distributions of ammonium sulfate were injected into the chamber and exposed to adiabatic expansions that simulated typical marine updraft velocities. Observations from the experiments were compared to model predictions from a one dimensional cloud model as well as other published modeling results. The dynamic cloud chamber, as configured for this study, was shown to be suitable for use in making stratus cloud simulations at updraft velocities greater than 1.0 m s-1. Mean diameter, liquid water content and dispersion coefficient values appeared to be comparable to the model predictions. Nucleated aerosol fraction trends agreed with model results. Details of the design, implementation and data interpretation are presented.