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Browsing by Author "Kreidenweis, Sonia, committee member"

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    A simple parameterization of aerosol emissions in RAMS
    (Colorado State University. Libraries, 2013) Letcher, Theodore, author; Cotton, William, advisor; Kreidenweis, Sonia, committee member; Ramirez, Jorge, committee member
    Throughout the past decade, a high degree of attention has been focused on determining the microphysical impact of anthropogenically enhanced concentrations of Cloud Condensation Nuclei (CCN) on orographic snowfall in the mountains of the western United States. This area has garnered a lot of attention due to the implications this effect may have on local water resource distribution within the Region. Recent advances in computing power and the development of highly advanced microphysical schemes within numerical models have provided an estimation of the sensitivity that orographic snowfall has to changes in atmospheric CCN concentrations. However, what is still lacking is a coupling between these advanced microphysical schemes and a real-world representation of CCN sources. Previously, an attempt to representation the heterogeneous evolution of aerosol was made by coupling three-dimensional aerosol output from the WRF Chemistry model to the Colorado State University (CSU) Regional Atmospheric Modeling System (RAMS) (Ward et al. 2011). The biggest problem associated with this scheme was the computational expense. In fact, the computational expense associated with this scheme was so high, that it was prohibitive for simulations with fine enough resolution to accurately represent microphysical processes. To improve upon this method, a new parameterization for aerosol emission was developed in such a way that it was fully contained within RAMS. Several assumptions went into generating a computationally efficient aerosol emissions parameterization in RAMS. The most notable assumption was the decision to neglect the chemical processes in formed in the formation of Secondary Aerosol (SA), and instead treat SA as primary aerosol via short-term WRF-CHEM simulations. While, SA makes up a substantial portion of the total aerosol burden (much of which is made up of organic material), the representation of this process is highly complex and highly expensive within a numerical model. Furthermore, SA formation is greatly reduced during the winter months due to the lack of naturally produced organic VOC's. Because of these reasons, it was felt that neglecting SOA within the model was the best course of action. The actual parameterization uses a prescribed source map to add aerosol to the model at two vertical levels that surround an arbitrary height decided by the user. To best represent the real-world, the WRF Chemistry model was run using the National Emissions Inventory (NEI2005) to represent anthropogenic emissions and the Model Emissions of Gases and Aerosols from Nature (MEGAN) to represent natural contributions to aerosol. WRF Chemistry was run for one hour, after which the aerosol output along with the hygroscopicity parameter (κ) were saved into a data file that had the capacity to be interpolated to an arbitrary grid used in RAMS. The comparison of this parameterization to observations collected at Mesa Verde National Park (MVNP) during the Inhibition of Snowfall from Pollution Aerosol (ISPA-III) field campaign yielded promising results. The model was able to simulate the variability in near surface aerosol concentration with reasonable accuracy, though with a general low bias. Furthermore, this model compared much better to the observations than did the WRF Chemistry model using a fraction of the computational expense. This emissions scheme was able to show reasonable solutions regarding the aerosol concentrations and can therefore be used to provide an estimate of the seasonal impact of increased CCN on water resources in Western Colorado with relatively low computational expense.
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    A theoretical and numerical investigation of warm-phase microphysical processes
    (Colorado State University. Libraries, 2015) Igel, Adele, author; van den Heever, Susan, advisor; Kreidenweis, Sonia, committee member; Rutledge, Steven, committee member; Oprea, Iuliana, committee member
    Several studies examining microphysical processes are conducted with an emphasis on further understanding warm-phase processes, particularly condensation. In general, these studies progress from simple to complex representations of microphysical processes in models. In the first study, a theoretical, analytical expression for the condensational invigoration, that is the invigoration in the warm-phase of a cloud due to changes in the condensation rate, of a polluted, cloudy parcel of air relative to a clean, cloudy parcel of air is developed. The expression is shown to perform well compared to parcel model simulations, and to accurately predict the invigoration to within 30% or less. The expression is then used to explore the sensitivity of invigoration to a range of initial conditions. It is found that the invigoration, in terms of added kinetic energy, is more sensitive to the cloud base temperature than to the initial buoyancy of the parcels. Changes in vertical velocity between clean and polluted parcels of up to 4.5 m s−1 at 1 km above cloud base are theoretically possible, and the difference in vertical velocity decreases when the initial vertical velocity of either parcel is large. These theoretical predictions are expected to represent an upper limit to the magnitude of condensational invigoration and should be applicable to both shallow cumulus clouds as well as the warm phase of deep convection. In the second study, the focus shifts to the comparison of the representation of microphysical processes in single- and double-moment microphysics schemes. Single-moment microphysics schemes have long enjoyed popularity for their simplicity and efficiency. However, it is argued that the assumptions inherent in these parameterizations can induce large errors in the proper representation of clouds and their feedbacks to the atmosphere. For example, precipitation is shown to increase by 200% through changes to fixed parameters in a single-moment scheme and low cloud fraction in the RCE simulations drops from ~15% in double-moment simulations to ~2% in single-moment simulations. This study adds to the large body of work that has shown that double-moment schemes generally outperform single-moment schemes. It is recommended that future studies, especially those employing cloud-resolving models, strongly consider moving to the exclusive use of multi-moment microphysics schemes. An alternative to multi-moment schemes is a bin scheme. In the third study, the condensation rates predicted by bin and bulk microphysics schemes in the same model framework are compared in a novel way using simulations of non-precipitating shallow cumulus clouds. The bulk scheme generally predicts lower condensation rates than does the bin scheme when the saturation ratio and the integrated diameter of the droplet distribution are identical. Despite other fundamental disparities between the bin and bulk condensation parameterizations, the differences in condensation rates are predominantly explained by accounting for the width of the cloud droplet size distributions simulated by the bin scheme which can alter the rates by 50% or more in some cases. The simulations are used again in the fourth study in order to further investigate the dependency of condensation and evaporation rates to the shape parameter and how this dependency impacts the microphysical and optical properties of clouds. The double-moment bulk microphysics simulations reveal that the shape parameter can lead to large changes in the average condensation rates, particularly in evaporating regions of the cloud where feedbacks between evaporation and the depletion of individual droplets magnify the dependency of the evaporation rate on the shape parameter. As a result the average droplet number concentration increases as the shape parameter increases, but changes to the cloud water content are small. Taken together, these impacts lead to a decrease in the average cloud albedo. Finally, the simulations indicate that the value of the shape parameter in subsaturated cloudy air is more important than the value in supersaturated cloudy air, and that a constant shape parameter may not be a poor assumption for simulations of non-precipitating shallow cumulus clouds.
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    Aerosol size distribution changes in FIREX-AQ biomass burning plumes: the role of plume concentration on coagulation and OA condensation/evaporation
    (Colorado State University. Libraries, 2022) June, Nicole, author; Pierce, Jeffrey, advisor; Kreidenweis, Sonia, committee member; Jathar, Shantanu, committee member
    The evolution of organic aerosols and aerosol size distributions within smoke plumes are uncertain due to the variability in rates of coagulation and organic aerosol (OA) condensation/evaporation across different smoke plumes and potentially in different locations within a single plume. We use aircraft data from the western US portion of the FIREX-AQ campaign to evaluate differences in aerosol size distribution evolution (growing by 10s to over 100 nm in several hours), OA mass, and Oxygen to Carbon ratios (O:C) under different concentrations and amounts of dilution. The observations show diameter increasing more quickly in more concentrated plumes despite these plumes generally having more OA evaporation than in the less concentrated plumes. Initial observations of OA and O:C suggest that evaporation and/or secondary OA formation between emission and the first measurement is also influenced by plume concentration. We estimate the isolated role of coagulation on size changes using model simulations, and we estimate the role of OA condensation/evaporation on size changes using the observed time evolution of the observed OA enhancement. We find that coagulation alone explains the majority of the diameter growth in the transect averages, with more growth occurring in plumes with higher initial number and OA concentrations. Overall, for each of the smoke plumes analyzed, including OA evaporation/condensation has a relatively minor impact on the simulated diameter compared to the changes due to coagulation. Additionally, we examine differences in evolution between the dilute and concentrated sections of the plume based on CO concentration to expand the range of plume concentrations represented in the observations. To determine if these in-plume concentration gradients could be used to understand smoke plumes outside of the range of the sampled average concentration, we simulate the dilute and concentrated plume regions independently (no mixing). In these simulations of each smoke plume region, the model underestimates particle growth in the less-concentrated regions of the plume and overestimates particle growth in the more-concentrated regions. This poor comparison suggests that turbulent mixing between the more- and less-concentrated regions is occurring on timescales too fast for the regions to evolve independently, but slow enough that aerosol size differences are still seen between the regions. The mixing in the plume limits the ability for our conclusions on variations in growth and condensation/evaporation within a plume to be applied to other plumes of a similar concentration. Overall, we conclude that coagulation dominates growth with plume concentrations being important in determining how much coagulational growth is observed.
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    Air quality impacts from unconventional oil and gas development
    (Colorado State University. Libraries, 2024) Ku, I-Ting, author; Collett, Jeffrey L., Jr., advisor; Fischer, Emily V., committee member; Carlson, Kenneth H., committee member; Kreidenweis, Sonia, committee member
    Unconventional oil and natural gas development (UOGD) has expanded rapidly across the United States raising concerns about associated air quality impacts. While significant effort has been made to quantify and limit methane emissions, relatively few observations have been made of emitted Volatile Organic Compounds (VOCs). Extensive air monitoring during development of several large, multi-well pads in Broomfield, Colorado, in the Denver-Julesburg Basin, provides a novel opportunity to examine changes in local concentrations of air toxics and other VOCs during drilling and completions of new wells. With simultaneous measurements of methane and 50 VOCs from October 2018 to December 2022 at as many as 19 sites near well pads, in adjacent neighborhoods, and at a more distant reference location, we identify impacts from each phase of well development and production. In Part 1, we report how emissions from Broomfield pre-production and production operations influence air toxics and other VOC concentrations at nearby locations. Use of weekly, time-integrated canisters, a Proton Transfer Reaction Mass Spectrometer (PTR-MS), continuous photoionization detectors (PID) to trigger canister collection upon detection of VOC-rich plumes, and an instrumented vehicle, provided a powerful suite of measurements to characterize both transient plumes and longer-term changes in air quality. Prior to the start of well development, VOC gradients were small across Broomfield. Once drilling commenced, concentrations of oil and gas (O&G) related VOCs, including alkanes and aromatics, increased around active well pads. Concentration increases were clearly apparent during certain operations, including drilling, coil tubing/millout operations, and production tubing installation. Emissions of C8-C10 n-alkanes during drilling operations highlighted the importance of VOC emissions from a synthetic drilling mud chosen to reduce odor impacts. More than 90 transient plumes were sampled and connected with specific UOGD operations. The chemical signatures of these plumes differed by operation type. Concentrations of individual, O&G-related VOCs in these plumes were often several orders of magnitude higher than in background air, with maximum ethane and benzene concentrations of 79,600 and 819 ppbv, respectively. Study measurements highlight future emission mitigation opportunities during UOGD operations, including better control of emissions from shakers that separate drill cuttings from drilling mud, production separator maintenance operations, and periodic emptying of sand cans during flowback operations. In Part 2 OH reactivities (OHR) were calculated to examine the potential of emitted VOCs to contribute to regional ozone formation. NO2 was the largest contributor to OHR during winter when OHR values peaked, while VOCs dominated OH sinks during summer. Oxygenated VOCs and C3-C7 n-alkanes, closely associated with O&G activities, were primary contributors to OHR levels during the summer ozone season. In Part 3 we leverage observations from Broomfield and other Colorado O&G air quality studies to examine relationships between O&G emissions of methane and VOCs. A key goal is to determine whether more commonly measured methane emissions can serve as a surrogate to estimate emissions of less frequently measured compounds such as benzene, a key air toxic. While strong correlations are observed between benzene and methane emissions in some situations, considerable variability is observed in this relationship across locations and operations suggesting caution in assuming that reductions in methane emissions will yield proportionate reductions in releases of air toxics.
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    An observational and theoretical investigation of the evolution of biomass burning aerosol size distributions
    (Colorado State University. Libraries, 2015) Sakamoto, Kimiko M., author; Pierce, Jeffrey, advisor; Kreidenweis, Sonia, committee member; Volckens, John, committee member
    Biomass-burning aerosols contribute to aerosol radiative forcing on the climate system. The magnitude of this effect is partially determined by aerosol size distributions, which are functions of source fire characteristics (e.g. fuel type, MCE) and in-plume microphysical processing (occurring on a GCM sub-grid scale). The uncertainties in biomass-burning emission number size-distributions in climate model inventories lead to uncertainties in the CCN concentrations and forcing estimates derived from these models. This emphasizes the need for observational and modelling studies to better represent effective biomass-burning size-distributions in larger-gridbox models. The BORTAS-B measurement campaign was designed to sample boreal biomass-burning outflow over Eastern Canada in the summer of 2011. Using these BORTAS-B data, we implement plume criteria to isolate the characteristic size-distribution of aged biomass-burning emissions (aged ~ 1 - 2 days) from boreal wildfires in Northwestern Ontario. The composite median size-distribution yields a single dominant accumulation mode with Dpm = 230 nm (number-median diameter), σ = 1.5, which are comparable to literature values of other aged plumes of a similar type. The organic aerosol enhancement ratios (ΔOA/ΔCO) along the path of Flight b622 show values of 0.05-0.18 μg m⁻³ ppbv⁻¹ with no significant trend with distance from the source. This lack of enhancement ratio increase/decrease with distance suggests no detectable net OA production/evaporation within the aged plume over the sampling period. A Lagrangian microphysical model was used to determine an estimate of the freshly emitted size distribution and flux corresponding to the BORTAS-B aged size-distributions. The model was restricted to coagulation and dilution processes only based on the insignificant net OA production/evaporation derived from the ΔOA/ΔCO enhancement ratios. We estimate that the fresh-plume median diameter was in the range of 59-94 nm with modal widths in the range of 1.7-2.8 (the ranges are due to uncertainty in the entrainment rate). Thus, the size of the freshly emitted particles is relatively unconstrained due to the uncertainties in the plume dilution rates. Expanding on the fresh-plume coagulational modelling of the BORTAS-B plumes, a coagulation-only parameterization for effective biomass-burning size-distributions was developed using the SAM-TOMAS plume model and a gaussian emulator. Under a range of biomass-burning conditions, the SAM-TOMAS simulations showed increasing Dpm and decreasing σ (converging to 1.2) with distance from the emission source. Final Dpm also shows a strong dependence on dM/dx (Mass flux x Fire area/vg), with larger values resulting in more rapid coagulation and faster dDpm/dt. The SAM-TOMAS simulations were used to train the Gaussian Emulation Machine for Sensitivity Analysis (GEM-SA) to build a Dpm and σ parameterization based on seven inputs. The seven inputs are: emission Dpm0, emission σ0, mass flux, fire area, mean boundary layer wind (vg), time, and plume mixing depth (dmixing). These inputs are estimated to account for 81% of the total variance in the final size distribution Dpm, and 87% of the total variance in the final σ. The parameterization performs very well against non-training modelled SAM-TOMAS size-di stributions in both final Dpm (slope = 0.92, R² = 0.83, NMBE=-0.06) and final σ (slope = 0.91, R² = 0.93, NMBE = 0.01). These final size distribution parameters are meant to be inserted as effective biomass-burning aerosol size-distributions (single lognormal mode) into larger-scale atmospheric models.
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    Analysis of multiple new-particle growth pathways observed at the US DOE Southern Great Plains Field Site
    (Colorado State University. Libraries, 2016) Hodshire, Anna, author; Pierce, Jeff, advisor; Barsanti, Kelley, committee member; Farmer, Delphine, committee member; Kreidenweis, Sonia, committee member
    New-particle formation (NPF) is a significant source of aerosol particles to the atmosphere. However, these particles are initially too small to have climatic importance and must grow, primarily through net uptake of low-volatility species, from diameters 1 nm to 30-100 nm in order to potentially impact climate. There are currently uncertainties in the physical and chemical processes associated with the growth of these freshly formed particles that lead to uncertainties in aerosol-climate modeling. Four main pathways for new-particle growth have been identified: condensation of sulfuric acid vapor (and associated bases when available), condensation of organic vapors, uptake of organic acids through acid-base chemistry in the particle phase, and accretion of organic molecules in the particle phase to create a lower-volatility compound that then contributes to the aerosol mass. The relative importance of each pathway is uncertain and may vary by geographic location and atmospheric conditions. Assessing the relative importance is the focus of this work. The 2013 New Particle Formation Study (NPFS) measurement campaign took place at the DOE Southern Great Plains (SGP) facility in Lamont, Oklahoma, during spring 2013. Measured gas-and particle-phase compositions during these new-particle growth events suggest three distinct growth pathways: (1) growth by primarily organics; (2) growth by primarily sulfuric-acid/ammonia; and (3) growth by primarily sulfuric-acid/bases/organics. To supplement the measurements, we used the particle-growth model MABNAG (Model for Acid-Base chemistry in NAnoparticle Growth) to gain further insight into the growth processes on these three days at SGP. MABNAG simulates growth from (1) sulfuric-acid condensation (and subsequent salt formation with ammonia or amines); (2) near-irreversible condensation from non-reactive extremely-low-volatility organic compounds (ELVOCs); and (3) organic-acid condensation and subsequent salt formation with ammonia or amines. MABNAG is able to corroborate the observed differing growth pathways, while also predicting that ELVOCs contribute more to growth than organic salt formation. However, most MABNAG model simulations tend to underpredict the observed growth rates between 10-20 nm in diameter; this underprediction may come from neglecting the contributions to growth from semi-to-low-volatility species or accretion reactions. Our results suggest that in addition to sulfuric acid, ELVOCs are also very important for growth in this rural setting. We discuss the limitations of our study that arise from not accounting for semi- and low-volatility organics, as well as nitrogen-containing species beyond ammonia and amines in the model. Quantitatively understanding the overall budget, evolution, and thermodynamic properties of lower-volatility organics in the atmosphere will be essential for improving global aerosol models.
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    Assessing the impacts of cloud condensation nuclei on cumulus congestus clouds using a cloud resolving model
    (Colorado State University. Libraries, 2011) Sheffield, Amanda M., author; van den Heever, Susan C., advisor; Kreidenweis, Sonia, committee member; Eykholt, Richard, committee member
    Cumulus congestus clouds are mid-level clouds that form part of the trimodal tropical cloud distribution. They act to moisten the atmosphere and may become mixed-phase in their lifetime. Congestus typically surpass the tropical trade wind inversion from where they may either develop into deeper convection, or alternatively remain as terminal congestus. Such growth is dependent on multiple factors, including those which alter the local environment and the microphysical structure of the cloud. This study investigates the impacts of cloud condensation nuclei (CCN) on cumulus congestus clouds through the use of large domain, cloud-resolving model (CRM) simulations in radiative convective equilibrium (RCE). Previous studies have focused on the convective invigoration of congestus and their subsequent growth to deep convection in association with ice processes. This study will focus on the response of congestus clouds to more polluted conditions, with particular emphasis on the development and growth of congestus from the warm phase to beyond the freezing level. It is found that convection is invigorated in the more polluted cases in association with the enhanced latent heat released during the vapor diffusional growth of cloud droplets in the warm phase. Such invigoration results in stronger updraft speeds, enhanced vertical lofting of cloud water, and a subsequent increase in the number of clouds growing to above the freezing level. The lofted cloud water is available to form more ice, however the ice water produced is smaller in magnitude compared to cloud water amounts above the freezing level. The low amounts of ice result in relatively insignificant contributions of the latent heat of freezing to the updraft strength. The impacts of enhanced CCN concentrations on various other cloud characteristics and microphysical processes are also investigated.
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    Climate and health impacts of particulate matter from residential combustion sources in developing countries
    (Colorado State University. Libraries, 2018) Kodros, John K., author; Pierce, Jeffrey R., advisor; Volckens, John, committee member; Kreidenweis, Sonia, committee member; Ravishankara, A. R., committee member
    Globally, close to 2.8 billion people lack access to clean cooking technology, while 1.8 billion people lack access to electricity altogether. As a means to generate energy for residential tasks, it is common in many developing countries to rely on combustion of solid fuels (wood, dung, charcoal, trash, etc.). Solid fuel use (SFU) can emit substantial amounts of fine particulate matter (PM2.5), often in or in close proximity to residences, creating concerns for human health and climate; however, large uncertainties exist in indoor and outdoor concentrations and properties, limiting our ability to estimate these climate and health impacts. This work explores the uncertainty space in estimates of premature mortality attributed to exposure to PM2.5 from residential SFU (e.g., cooking, heating, lighting) and makes the first estimates of health and radiative effects from combustion of domestic waste (i.e., trash burning). Next, we investigate key uncertain parameters (emission size distribution, black carbon mixing state, and size-resolved respiratory deposition) that drive uncertainties in health and radiative impacts from SFU, in order to improve model estimates of aerosol impacts from all sources. In many developing regions, combustion of solid fuels for cooking and heating is not the only aerosol source impacting air quality and climate. While uncontrolled combustion of domestic waste has been observed in many countries, this aerosol source is not generally included in many global emissions inventories. Using a global chemical-transport model, we estimate exposure to ambient PM2.5 from domestic-waste combustion to cause 270,000 (5th-95th percentile: 213,000 to 328,000) adult mortalities per year, most of which occur in developing countries. Regarding aerosol radiative effects, we estimate the globally averaged direct radiative effect (DRE) to range from -40 mW m-2 to +4 mW m-2 and the aerosol indirect effect (AIE) to range from -4 mW m-2 to -49 mW m-2. In some regions with significant waste combustion, such as India and China, the aerosol radiative effects exceed −0.4 W m−2.The sign and magnitude of the global-mean DRE is strongly sensitive to assumptions on how black carbon (BC) is mixed with scattering particles, while the AIE is strongly sensitive to the emission size distribution. To determine what factors dominate the uncertainty space in mortality estimates from SFU, we perform a variance-based sensitivity analysis on premature mortality attributed to the combined exposure to ambient and household PM2.5 from SFU. We find that uncertainty in the percent of the population using solid fuels for energy contributes the most to the uncertainty in mortality (53-56% of uncertainty across Asia and South America) with the concentration-response function the next largest contributor (40-50%). In the second half of this dissertation, we explore several key uncertainties in climate and health estimates of aerosol from residential sources in order to reduce overall model uncertainty of aerosol impacts from any source. To test the sensitivity of the AIE to treatment of aerosol size distributions in global models, we estimate the AIE due to anthropogenic emissions with prognostic sectional aerosol microphysics and compare this to the AIE calculated when the simulated aerosol mass of each species is remapped onto a prescribed size distribution. Simulations using the prognostic scheme yield a global mean anthropogenic AIE of −0.87 W m−2, while the simulations with the prescribed scheme predict −0.66 W m−2. These differences suggest that simulations with prescribed size‐distribution mapping are unable to capture regional and temporal variability in size‐resolved aerosol number and thus may lead to biases in estimates of the AIE.
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    Combined multispectral/hyperspectral remote sensing of tropospheric aerosols for quantification of their direct radiative effect
    (Colorado State University. Libraries, 2013) McGarragh, Gregory R., author; Stephens, Graeme, advisor; Kreidenweis, Sonia, committee member; Vonder Haar, Thomas, committee member; Bartels, Randy, committee member
    Scattering and absorption of solar radiation by aerosols in the atmosphere has a direct radiative effect on the climate of the Earth. Unfortunately, according to the IPCC the uncertainties in aerosol properties and their effect on the climate system represent one of the largest uncertainties in climate change research. Related to aerosols, one of the largest uncertainties is the fraction of the incident radiation that is scattered rather than absorbed, or their single scattering albedo. In fact, differences in single scattering albedo have a significant impact on the magnitude of the cooling effect of aerosols (opposite to that of greenhouse gasses) which can even have a warming effect for strongly absorbing aerosols. Satellites provide a unique opportunity to measure aerosol properties on a global scale. Traditional approaches use multispectral measurements of intensity at a single view angle to retrieve at most two aerosol parameters over land but it is being realized that more detail is required for accurate quantification of the direct effect of aerosols, in particular its anthropogenic component, and therefore more measurement information is required. One approach to more advanced measurements is to use not only intensity measurements but also polarimetric measurements and to use multiple view angles. In this work we explore another alternative: the use of hyperspectral measurements in molecular absorption bands. Our study can be divided into three stages the first of which is the development of a fast radiative transfer model for rapid simulation of measurements. Our approach is matrix operator based and uses the Padé approximation for the matrix exponential to evaluate the homogeneous solution. It is shown that the method is two to four times faster than the standard and efficient discrete ordinate technique and is accurate to the 6th decimal place. The second part of our study forms the core and is divided into two chapters the first of which is a rigorous sensitivity and optimal estimation based information content study that explores the use of measurements made by a MODIS type instrument combined with measurements made by an instrument similar to GOSAT TANSO-FTS which supplies hyperspectral measurements of intensity and polarization in the O2 A-band and the 1.61- and 2.06-μm CO2 bands. It is found that the use of the hyperspectral bands provides a means to separate the effects of the surface and aerosol absorption from effects related to aerosol single scattering parameters. The amount of information increases significantly when the CO2 bands are included rather than just the more traditional O2 A-band, when polarization measurements are included, and when measurements are made at multiple view angles. We then present a retrieval using co-located observations of MODIS and GOSAT TANSO-FTS which are both also co-located with AERONET sites for validation purposes. We introduce an optimal estimation retrieval and perform this retrieval on our co-located observations. We choose a complete state vector to maximize the use of the information in our measurements and use an a priori constraint and regularization to arrive at a stable solution. In addition to the retrieved parameters, we also calculate a self contained estimation of the retrieval error. Validation with AERONET, for retrievals using MODIS plus TANSO-FTS measurements of intensity and polarization in all three bands indicate accuracies within 15% for optical thickness, 10% for fine mode mean radius, 35% for coarse mode mean radius, 15% for the standard deviation of fine mode mean radius, 25% for the standard deviation of the coarse mode mean radius, 0.04 for the real part of the index of refraction, and 0.05 for single scattering albedo. In addition to the retrieved parameters, we also validate the estimated retrieval error and find that the estimations have distributions that are tighter and within the broader distributions of real errors relative to AERONET. The third part of our study uses the retrieval results to calculate radiative fluxes, errors, and sensitivities at solar wavelengths along with aerosol radiative effect and effect efficiency. In addition, we outline how to propagate the errors in the retrieval through the flux calculations to provide an error estimation of the fluxes. These results are then validated against the corresponding AERONET products. It was found that the flux results were most sensitive to single scattering albedo while the size distribution and real part of the index of refraction also have significant effects. Relative to AERONET our fluxes are less accurate than an independent AERONET validation, due to uncertainties in our satellite based retrieval with accuracies within 13 Wm-2 for TOA upward, 9 Wm-2 for BOA upward, and 30 Wm-2 for BOA downward. The estimated errors also contained uncertainties but were in fact more conservative than the actual errors.
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    Design of an inhalable aerosol size spectrometer
    (Colorado State University. Libraries, 2015) Ndonga, Mwangi, author; Volckens, John, advisor; Reynolds, Stephen, committee member; Kreidenweis, Sonia, committee member
    Industrial hygienists lack the proper instruments to measure size distributions of inhalable particulate matter (0-100 μm) as defined by ACGIH/ISO/CEN. The Portable Inhalable Particle Spectrometer (PIPS) was designed to size-segregate IPM in calm-air environments – which constitute a majority of workplaces. The PIPS uses an upward air velocity to restrict particle aspiration into the device to diameters above a specified cut-size. A vertical test chamber was also designed to facilitate aerosol dispersion and experimental evaluation of the PIPS. Two PIPS tubes were tested (1.5 cm and 5 cm) at four face velocities (0.6, 1.35, 2.5 and 3.5 cm·s⁻¹) that correspond to cut-sizes of 20, 30, 40 and 50 μm in aerodynamic diameter, respectively. The observed performance of the PIPS deviated from model estimates as face velocity or tube diameter was increased. The fluid regime present inside the chamber, due to the operating PIPS, likely influenced the measured sampling efficiency of the PIPS.
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    Development of framework for predicting water production from oil and gas wells in Wattenberg field, Colorado
    (Colorado State University. Libraries, 2012) Bai, Bing, author; Carlson, Kenneth, advisor; Grigg, Neil, committee member; Kreidenweis, Sonia, committee member
    Water issues in the oil and gas industry have drawn attention from various stakeholders including the public, industry and environmental groups. With the increasing demand for energy, the number of oil and gas wells has increased greatly providing 60% of the energy in the United States. Besides the large volume of fresh water required for drilling and hydraulic fracturing, wastewater from the well can also lead to serious problems. The current approach for managing wastewater from oil and gas fields is deep well injection or evaporation both of which can potentially cause environmental issues. One of the best strategies to solve water issues from oil and gas operations is to reuse wastewater as drilling and fracturing water so the volume of fresh water required and wastewater disposed can be reduced. Information on both water quantity and quality are required when designing wastewater reuse treatment facilities. This study provides a framework for understanding water production trends from oil and gas wells in the Wattenberg field in Northern Colorado by analyzing historical data from Noble Energy Inc. The Arps equations were chosen for modeling water production from oil and gas wells. After studying 1,677 vertical and 32 horizontal wells in Wattenberg field, an exponential decline function was applied to model the produced water production of all the wells and the frac flowback water of horizontal wells. An Excel based 30-year water production prediction tool was developed based on the two protocols developed for vertical and horizontal wells in the Wattenberg field. Three case studies of different subsets of oil and gas wells were examined to illustrate the function of the tool. In addition, a comparison of exponential and harmonic functions was made in the third case study, and a significant difference was observed. The harmonic decline function predicts a less aggressive decline resulting in higher production volumes. It was concluded that in the absence of long term production data, the harmonic decline function should be used since the exponential decline function may underestimate the volume of produced water.
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    Effects of near-source coagulation of biomass burning aerosols on global predictions of aerosol size distributions and implications for aerosol radiative effects
    (Colorado State University. Libraries, 2018) Ramnarine, Emily, author; Pierce, Jeffrey, advisor; Kreidenweis, Sonia, committee member; Jathar, Shantanu, committee member
    Biomass burning is a significant global source of aerosol number and mass. In fresh biomass burning plumes, aerosol coagulation reduces aerosol number and increases the median size of aerosol size distributions, impacting aerosol radiative effects. Near-source biomass burning aerosol coagulation occurs at spatial scales much smaller than the grid boxes of global and many regional models. To date, these models ignore sub-grid coagulation and instantly mix fresh biomass burning emissions into coarse grid boxes. A previous study found that the rate of particle growth by coagulation within an individual smoke plume can be approximated using the aerosol mass emissions rate, initial size distribution median diameter and modal width, plume mixing depth, and wind speed. In this thesis, we use this parameterization of sub-grid coagulation in the GEOS-Chem-TOMAS global aerosol microphysics model to quantify the impacts on global aerosol size distributions, the direct radiative effect, and the cloud-albedo aerosol indirect effect. We find that inclusion of biomass burning sub-grid coagulation reduces the biomass burning impact on the number concentration of particles larger than 80 nm (a proxy for CCN-sized particles) by 37% globally. This CCN reduction causes our estimated global biomass burning cloud-albedo aerosol indirect effect to decrease from -76 to -43 mW m−2. Further, as sub-grid coagulation moves mass to sizes with more efficient scattering, including it increases our estimated biomass burning all-sky direct effect from -224 to -231 mW m−2 with assumed external mixing and from -188 to -197 mW m−2 with assumed internal mixing with core-shell morphology. However, due to differences in fire and meteorological conditions across regions, the impact of sub-grid coagulation is not globally uniform. We also test the sensitivity of the impact of sub-grid coagulation to two different biomass burning emission inventories, to various assumptions about the fresh biomass burning aerosol size distribution, and to two different timescales of sub-grid coagulation. The impacts of sub-grid coagulation are qualitatively the same regardless of these assumptions.
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    Exploring nanoaggregate structures of model asphaltenes using two dimensional infrared spectroscopy
    (Colorado State University. Libraries, 2015) Cyran, Jenée D., author; Krummel, Amber T., advisor; Bernstein, Elliot, committee member; Levinger, Nancy, committee member; Borch, Thomas, committee member; Kreidenweis, Sonia, committee member
    Asphaltenes have been an enigma in the scientific community; studies on the molecular masses have differed by orders of magnitude and structures have been debated between island or archipelago structures. Thus, the asphaltene community defines asphaltenes by their solubility. Asphaltenes are n-heptane-insoluble and toluene-soluble. The known nanoaggregation of asphaltenes at different timescales and concentrations causes issues to determine the molecular weight and structure of asphaltene molecules. This thesis is the first step to using two dimensional infrared (2D IR) spectroscopy to study the nanoaggregate structure of model asphaltenes. 2D IR spectroscopy is a vibrational spectroscopy that is advantageous over linear IR absorption due to the ability to spread the spectral information over two axes. The 2D IR spectra give rise to structurally sensitive cross-peaks, affording the ability to probe the structure of the nanoaggregates. The model asphaltenes used in this work are violanthrone-79 and lumogen orange, a perylene derivative. These model asphaltenes consist mostly of polycyclic aromatic hydrocarbons (PAHs), similar to asphaltenes. Violanthrone-79 and lumogen orange also have carbonyl functional groups, which provide vibrational probes. The carbonyl stretching and ring breathing vibrations are used to probe the stacked structure of the nanoaggregates. A quinone series of one, two and three ring systems was used to first study the coupling between the carbonyl stretching and ring breathing vibrational modes. The quinone series provided the foundation for the larger ring systems that emulate asphaltenes. The data from studying the stacked structure of nanoaggregate model asphaltenes can be used to reveal properties of nanoaggregate asphaltenes. This work will allow for continued study of the kinetics of nanoaggregation using 2D IR waiting time experiments for dynamic information. Thus, this work demonstrates the use of 2D IR spectroscopy, which offers femtosecond time resolution, as a viable technique for studying nanoaggregation.
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    Exploring post-cold frontal moisture transport in an idealized extratropical cyclone study
    (Colorado State University. Libraries, 2016) Sheffield, Amanda Marie, author; van den Heever, Susan C., advisor; Eykholt, Richard, committee member; Johnson, Richard, committee member; Kreidenweis, Sonia, committee member
    Moisture transport in extratropical cyclones (ETCs) has been studied in the past in the context of the warm conveyor belt (WCB), a 'conveyor belt' transferring moisture from the warm sector boundary layer to the free troposphere both eastward and poleward of the warm front. Recent research has highlighted a different, potentially important mechanism of transporting water vapor in ETCs by post-cold frontal (PCF) clouds. PCF clouds are typically boundary layer cumulus clouds located in the cold sector of an ETC that transfer moisture to the free troposphere through convective-evaporative processes. Recent studies have suggested that these PCF cumuli may vertically transport nearly equivalent amounts of moisture as the WCB. Therefore, not only are these PCF cumuli important in venting the PCF boundary layer, they also play a role in limiting the amount of moisture available for convergence in the source region of the WCB. This limitation can have important consequences for regional weather and climate through its impact on the timing and location of precipitation, the three-dimensional redistribution of water vapor, and the distribution of clouds within ETCs. The goal of this study is to investigate the role of PCF clouds in the moisture transport of an ETC, and the impacts of environmental factors such as SST and aerosol loading on this transport role. We have achieved this goal through the use of numerical simulations of such a storm system. Previous studies have utilized model simulations with relatively coarse grid resolutions and convective parameterization schemes. Here, we simulate a wintertime ETC over the Pacific Ocean using high spatial and temporal resolution, advanced microphysics and explicitly resolved convection. The results of this research demonstrate that PCF cumuli are found to vertically ventilate BL moisture over an expansive region behind the cold front. The free tropospheric moisture contents and stability profile of the cold sector exert a strong control over the size, depth and frequency of the PCF clouds, and varies with distance from the cold front. Increased aerosol loading results in the invigoration of the PCF clouds. This is associated with an increase in the upward vertical moisture flux, increased cloud condensate formation, and reduced precipitation rates. Sea surface temperature is found to be a significantly more important factor in the development of PCF cumuli than aerosol loading, where increasing SSTs are associated with increased cloud fraction, cloud top heights, and precipitation rates. The impact of PCF clouds on vertically redistributing water vapor from the cold sector is found to depend in varying degrees on the large-scale advection of water vapor by the ETC system, the surface evaporation rates, the updraft velocities, the precipitation rates, and the cloud fraction within the PCF region. The pathways of the vertically redistributed water vapor within the ETC were then examined through the use of massless, passive tracers. The results of these experiments show that the water vapor lofted out of the PCF BL by the cumulus clouds is advected hundreds of kilometers eastward within 8-12 hours of release of tracers in the PCF BL. Furthermore, cross frontal transport from behind the cold front to the WCB source region appears to be small, in contradiction to previously hypothesized results. This is due to the fact that the cold frontal boundary provides a zone of strong vertical lifting that does not allow tracers to converge further east.
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    Look up: probing the vertical profile of new particle formation and growth in the planetary boundary layer with models and observations
    (Colorado State University. Libraries, 2022) O'Donnell, Samuel, author; Pierce, Jeffrey, advisor; Jathar, Shantanu, committee member; Kreidenweis, Sonia, committee member
    The processes of new particle formation (NPF) and growth are important contributors to cloud condensation nuclei (CCN) concentrations, and CCN are important for climate from their impact on planetary radiative forcing. While the general ubiquity and importance of NPF is understood, the vertical extent and governing mechanisms of NPF and growth in the lower troposphere are uncertain. We present a two-part analysis of the vertical profile of NPF during the HI-SCALE field campaign at the Southern Great Plains observatory in Oklahoma, USA. Firstly, we analyzed airborne and ground-based observations of four NPF events. Secondly, we used a column aerosol chemistry and microphysics model, along with the observations, to probe factors that influence the vertical profile of NPF. During HI-SCALE, we found several instances of enhanced NPF occurring several hundred meters above the surface; however, the spatio-temporal characteristics of the observed NPF made comparisons between airborne- and ground-based observations difficult. For six unique events, the model represented the observed NPF (or lack of NPF) and particle growth at the surface to within 10 nm. The model predicted enhanced NPF rates in the upper mixed layer, and this enhancement is primarily due to the temperature dependence in the NPF schemes. The simulations were sensitive to the initial vertical profile of gas-phase species from HI-SCALE, such that vertical mixing in the model either enhanced or suppressed NPF rates, aerosol number concentrations, and particle growth rates at the surface. Finally, our analysis provides insights for future field campaigns and modeling efforts investigating the vertical profile of NPF.
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    Micrometeorological studies of a beef feedlot, dairy, and grassland: measurements of ammonia, methane, and energy balance closure
    (Colorado State University. Libraries, 2018) Shonkwiler, Kira Brianne, author; Collett, Jeffrey L., advisor; Ham, Jay M., committee member; Kreidenweis, Sonia, committee member; Schumacher, Russ, committee member; Archibeque, Shawn, committee member
    Ammonia emissions from concentrated animal feeding operations (CAFOs; most of which are beef feedlots) near the Colorado Front Range are suspected to be a large regional input of reactive nitrogen which has been found to accumulate and cause deleterious effects in nearby downwind Class I areas like Rocky Mountain National Park. Methane (CH4) is a strong greenhouse gas (GHG) emitted in large amounts from dairy anaerobic lagoons used for liquid manure management. Lagoon systems account for over half of the manure management-based CH4 emissions from agriculture in the US. There is a strong need for more emissions measurements from CAFOs like feedlots and dairies. For these data to be trusted, well-developed techniques must be utilized at emissions measurement sites and such techniques should be validated in ideal scenarios. Three micrometeorological studies were performed involving measurement of emissions using micrometeorological methods in the surface layer. The first study involved estimating summertime NH3 emissions from a 25,000-head beef feedlot in Northern Colorado. Two different NH3 sensors were used: a cavity ring down spectroscopy analyzer collected data at a single point while a long-path FTIR collected data along a 226-m long transect, both deployed along the same fenceline. Concentration data from these systems were used with two inverse dispersion models (FIDES, an inverse solution to the advection dispersion equation; and WindTrax, a backward Lagrangian stochastic model). Point sensor concentrations of NH3 were similar to line-integrated sensor concentrations suggesting some spatial uniformity in emissions. Emissions had a diurnal pattern (i.e., afternoon peak with minimum in early morning) that was driven by temperature. Emissions predicted by WindTrax were 25.2% higher than those from FIDES. Point vs. long-path measurements of NH3 had minimal effect on predicted emissions. The mean NH3 emission factor (EF) was 80 ± 39 g NH3 hd−1 d−1, with 40.0% of dietary-N emitted as NH3. The second study involved using eddy covariance and WindTrax to quantify CH4 emissions from a 3.9-ha anaerobic lagoon serving a 1400-head dairy in northern Colorado. Methane emissions followed a strong seasonal pattern correlated with temperature of the organic sludge layer on the bottom of the lagoon. Fluxes started increasing in late spring (May; ~10°C), increased rapidly in Jun (10-15°C) peaked in the summer (Jul/Aug; ~18-20°C) and remained high until mid-autumn (late Oct/early Nov; ~10°C). Fluxes then decreased and remained consistently low (up to 10 times less than peak emissions) until microbial activity ramped up again in May. The EC signal was very dependent on wind direction, with highest concentrations and fluxes associated with the direction of the lagoon. Gap-filled data showed a slight diurnal pattern to all seasons, with tenfold increases in diurnal values for summer over winter. Additionally, EFs for the lagoon varied by season with lows in the winter and highs in the summer with an annual mean of 819 ± 774 g CH4 hd-1 d-1. WindTrax overestimated EC for the lagoon (1163 ± 1049 g CH4 hd-1 d-1 versus 819 ± 774 g CH4 hd-1 d-1), but this difference may be attributable to differences in the sampling footprint and stability conditions. IPCC Tier 2-calculated EFs were extremely close to EC-based measurements and WT-based estimates. The third study involved using eddy covariance in an ideal environment (tallgrass prairie in Kansas) to test the reasons behind the "energy balance (EB) closure problem" at two landscape positions. This problem can cast uncertainty on flux measurements made by EC. One upland and one lowland EC tower each were used to measure EB components (i.e., net radiation, Rn; soil heat flux, G; total change in heat storage, deltaS; and sensible and latent heat fluxes, H and λE) during the summers of 2007 and 2008. To maximize closure, special attention was given to reduce all forms of instrumentation error and account for heat storage and photosynthesis between the soil and the reference height. Landscape position had little effect on G, H, and Rn; differences were ≤ 2% between sites. Lowland λE was 8% higher than upland λE because of greater biomass and soil moisture. On average, EB closure (i.e., Σ[λE+H] / Σ[Rn–G–ΔS]) was 0.88 and 0.94 at the upland and lowland sites, respectively. Closure was not correlated with friction velocity or the stability of the surface boundary layer. Given high confidence in Rn, G, and ΔS, turbulent fluxes depend directly on vertical velocity (w), and the fact that a systematic underestimation of w was recently found in literature, lack of closure may have resulted largely from anemometer-based underestimates of w.
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    Novel microfluidic devices for aerosol analysis
    (Colorado State University. Libraries, 2012) Mentele, Mallory M., author; Henry, Charles, advisor; Barisas, George, committee member; Reynolds, Melissa, committee member; Ladanyi, Branka, committee member; Kreidenweis, Sonia, committee member
    Widespread interest in microfluidic technology over the past 20 years has led to the development of microfluidic devices that are as varied in their complexity and capabilities as they are in the applications they are used for. This dissertation describes the development of two microfluidic devices, each designed for measurement of specific aerosol components. A microchip incorporating an interface between a continuous hydrodynamic sample flow and capillary electrophoresis separation was developed for analysis of atmospheric aerosols. The ability to separate and detect analytes from a continuous sample flow allows the microchip to be coupled to a particle-into-liquid aerosol sampler, providing a method for near real-time analysis of ionic aerosol components. Theoretical modeling of hydrodynamic and electroosmotic flows was used to predict flow behavior in the microchip and to optimize geometry. Separation and conductivity detection of common ionic aerosol components were carried out to observe device performance, and detection of nitrate and sulfate in Fort Collins air was accomplished with the coupled system. The simple design introduced here is the first example of a continuous flow microfluidic capillary electrophoresis device that incorporates conductivity detection, and is the first microfluidic device to be coupled to a continuous flow aerosol collector. A paper-based microfluidic device was also designed for the purpose of assessing occupational exposure to particulate metals. Assays were developed for colorimetric detection of metals on paper and these were employed in detection reservoirs of the device. A novel method was also developed for rapid digestion of particulate metals directly on a filter. Metal concentrations were quantified from color intensity images using a scanner in conjunction with image processing software. Finally, a standard incineration ash sample was aerosolized, collected on filters, and analyzed for the three metals of interest. This is the first paper-based device capable of multiplexed metal detection from a real, aerosolized sample.
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    NOx formation in methyl ester, alcohol, and alkane droplet autoignition and combustion: PLIF measurements and detailed kinetic modeling
    (Colorado State University. Libraries, 2014) Grumstrup, Torben, author; Marchese, Anthony J., advisor; Yalin, Azer, advisor; Kreidenweis, Sonia, committee member; Olsen, Daniel B., committee member
    Numerous studies have shown that diesel engines fueled by fatty-acid methyl ester biodiesel often exhibit slightly increased production of oxides of nitrogen (NOx) in comparison to petroleum diesel. A number of explanations for this increase have been proposed. One theory, which has been supported by optical engine test results, suggests that the presence of oxygen atoms in the methyl ester fuel molecule results in a leaner premixed autoignition zone, thereby increasing in-cylinder temperatures and promoting Zel'dovich NOx production. Other experiments have suggested that the unsaturated methyl esters in biodiesel cause an increase in CH radical production (and/or other potential precursors such as C2O) which in turn increases Fenimore NOx formation. In this work, these hypotheses are explored experimentally and computationally by considering autoignition and combustion of single, isolated methyl ester, alcohol and alkane droplets. Experiments were conducted in which the planar laser-induced fluorescence (PLIF) spectroscopy technique was applied to burning liquid fuel droplets in free-fall. A monodisperse stream of droplets was generated by a piezoelectric device and passed through a resistively heated ignition coil. A pulsed laser beam from a Nd:YAG-pumped dye laser (10 Hz, 10 ns width) was formed into a sheet and passed through the droplet flame. The dye laser was tuned to excite hydroxyl (OH) at 282.9 nm and nitric oxide (NO) at 226.0 nm. The resulting fluorescence was imaged by a Cooke Corporation DiCam Pro ICCD digital camera. Band pass filters were utilized to reject laser light scattering while admitting fluorescence wavelengths. Due to the small fluorescence signal, many fluorescence images were averaged together to create a useful average image; approximately 250 and 1000 images were averaged for OH and NO spectroscopy, respectively. Finally, pixel intensity of the averaged fluorescence image was integrated about the droplet center to create qualitative radial profiles of OH and NO concentration. Profiles were generated for a number of oxygenated fuels and one pure hydrocarbon: methanol, ethanol, 1-propanol, methyl butanoate, methyl decanoate, and n-heptane. To quantitatively interpret the contribution of Zel'dovich and Fenimore NOx mechanisms on NOx formation in the vicinity of igniting liquid droplets, detailed numerical droplet combustion simulations were conducted. The transient, spherically symmetric droplet combustion modeling featured detailed gas-phase kinetics, spectrally resolved radiant heat transfer, and multicomponent gas transport. New chemical kinetic mechanisms were created by appending NOx chemical kinetics to existing detailed methanol, methyl butanoate, and n-heptane mechanisms. In the computations, non-oxygenated (heptane) and oxygenated (methyl butanoate, methanol) fuel droplets are introduced into a hot (1150 K) air ambient whereupon the liquid vaporizes, thus producing a stratified fuel/air mixture that thermally autoignites after an ignition delay period. The computational results suggest that NOx formation in stratified fuel/air mixture in the vicinity of a cold liquid droplet is influenced greatly by the detailed full NOx chemistry (Fenimore, Zel'dovich and N2O) and cannot be fully explained by considering only the Zel'dovich NOx route. The computations also suggest, however, that the stoichiometry of the premixed autoignition zone in the laminar gas phase surrounding a spherical droplet differs from that observed in turbulent diesel spray ignition. In single droplets, irrespective of the fuel used, autoignition always initiates in the relatively hot lean region far from the droplet. In diesel sprays, depending on the thermodynamic conditions and fuel reactivity, ignition can occur in lean or rich regions by virtue of turbulent transport of heat and mass. In large molecular weight fuels like n-heptane or petroleum diesel fuel, this is often in mixtures which are quite rich (Φ ≈ 3). To underscore the difference between turbulent spray ignition and ignition of a single droplet, the most reactive mixture fraction and critical scalar dissipation rate were derived for the case of turbulent ignition The results show that for a turbulent non-premixed flame to ignite, two requirements must be met: (1) the fuel/air mixture fraction must be equal or similar to the most reactive mixture fraction, (2) the local scalar dissipation rate must be less than the critical scalar dissipation rate. Due to the effect of scalar dissipation rate on transport and mixing in turbulent, non-premixed flames, it is concluded that, at least as far as autoignition is concerned, autoignition of spherically-symmetric isolated fuel droplets has limitations as physical model for ignition of diesel sprays in compression ignition engines. However, the computations clearly show that transient NOx formation in presence of thermal and concentration gradients cannot be adequately described by the Zel'dovich NOx mechanism, which has consequences with regards to capability of computational engine simulations to accurately predict NOx formation.
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    Prediction of total lightning in Colorado and Alabama thunderstorms based on storm dynamical and microphysical variables
    (Colorado State University. Libraries, 2015) Basarab, Brett Michael, author; Rutledge, Steven, advisor; Deierling, Wiebke, committee member; Kreidenweis, Sonia, committee member; Reising, Steven, committee member
    Thunderstorms impact their environment in a variety of ways, including the production of nitrogen oxides (NOₓ) by lightning (LNOₓ). Accurate prediction of total lightning flash rate in thunderstorms is important to improve estimates of LNOₓ from the storm scale to the global scale. New flash rate parameterization schemes have been developed based on observed relationships between lightning flash rate and storm parameters for Colorado thunderstorms during the Deep Convective Clouds and Chemistry (DC3) experiment. Storm total flash rates are determined using an automated flash counting algorithm that clusters very high frequency (VHF) radiation sources emitted by electrical breakdown in clouds and detected by the northern Colorado lightning mapping array (LMA). Storm parameters such as hydrometeor echo volumes and ice masses are calculated from polarimetric radar retrievals. Measurements of updraft strength are obtained by synthesizing radial velocity retrievals from the CSU-CHILL and CSU-Pawnee radars to determine three-dimensional wind fields. Bulk storm parameters including the graupel echo volume, 30-dBZ echo volume, and precipitating ice mass are found to be robustly correlated to flash rate (R² ~ 0.8). It is shown that simple flash rate parameterization schemes based on these quantities predict gross flash rate behavior reasonably well. Updraft intensity-based flash rate schemes are also developed, but updraft parameters were not as strongly correlated to flash rate as storm volume quantities. The use of multiple storm parameters to predict flash rate is also investigated, since flash rate may be sensitive to multiple processes or characteristics within thunderstorms. A simple approach is found to be most effective: storm-total graupel and reflectivity echo volumes were split up into representative area and height dimensions and regressed against flash rate. The combined quantities predict flash rate variability somewhat better than simpler single-parameter flash rate schemes. All new flash rate schemes are tested against observations of Alabama thunderstorms documented during DC3 to examine their potential regional limitations. The flash rate schemes developed work best for strong Colorado storms with sustained high flash rates. Finally, relationships between total flash rate and flash size are discussed, with implications for the improved prediction of LNOₓ.
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    Spatial patterns and particle size distributions of atmospheric amines in northern Colorado
    (Colorado State University. Libraries, 2020) Bangs, Evelyn J., author; Collett, Jeffrey L., Jr., advisor; Kreidenweis, Sonia, committee member; Carter, Ellison, committee member; Benedict, Katherine B., committee member
    Emissions of reactive nitrogen along the Front Range in Northern Colorado have implications for sensitive and protected environments such as those in Rocky Mountain National Park (RMNP). Nitrogen-containing pollutants exert a variety of adverse effects on the environment, including visibility impairment and excessive nitrogen input to sensitive alpine ecosystems. Northern Colorado has many urban, agricultural, and oil and natural gas production activities that emit various forms of reactive nitrogen to the atmosphere. Model simulations and past measurements demonstrate that these emissions are capable of being transported long distances in gaseous and particulate forms. RMNP is particularly exposed to increased concentrations of reactive nitrogen pollutants during periods of easterly, upslope flow when emissions along the Front Range and sources from even farther away (e.g. the Western United States coast) are transported into the mountains. A detailed understanding of the composition of transported reactive nitrogen pollution is needed to predict environmental impacts within RMNP. While emissions of ammonia and nitrogen oxides have received significant attention in previous studies, relatively little is known about organic nitrogen pollution, despite its ability to contribute to excess N deposition and to formation of particulate matter (PM). Amines are organic analogs of ammonia, where one or more hydrogen atoms are replaced by organic functional groups. The animal agriculture industry is known to be a major source of some amines, while the beer and wine industry, sugar beet industry, leather manufacturing, and chemical manufacturing are also potentially important sources. Many of these industries are located along Colorado's Front Range, providing a good opportunity to study amine atmospheric chemistry. While the chemical lifetime of many gas phase amines is relatively short (hours), they are strong bases that can compete with ammonia to form longer-lived particles that are transported over substantial distances. The work carried out in this study focused on assessing a spatial gradient of particulate amines between RMNP, Fort Collins, and Greeley. Greater concentrations of many amines were typically observed near source emissions in Greeley and/or Fort Collins, but significant concentrations of amines such as dimethylamine, were also observed in the more remote environment at RMNP. To better understand amines, their chemistry and their contribution to PM, size distributions of 16 different amines were analyzed from measurements with a Micro-Orifice Uniform Deposit Impactor (MOUDI). Of 16 analyzed amines, nine were found above the detection limits in summertime Fort Collins and five during the winter. Several organic acids and inorganic acid anions particle size distributions were also assessed to understand contributions from potential anion species involved in salt formation with amine cations. Organic acid particle size distributions, particularly oxalate, overlap with fine particle mode size distributions of both ammonia and amine cations. The size distribution measurements also reveal important reactions between gaseous nitric acid and coarse soil particles to generate coarse mode nitrate particles. Continued measurements of amines and other species size distributions and spatial gradients at more locations would help improve understanding of amine PM chemistry. This understanding would allow necessary changes to be made to better protect the health of living beings and the sensitive ecosystems like those found in Rocky Mountain National Park.