Browsing by Author "Kreidenweis, Sonia, advisor"
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Item Unknown Characteristics of atmospheric ice nucleating particles associated with biomass burning in the US: prescribed burns and wildfires(Colorado State University. Libraries, 2013) McCluskey, Christina S., author; Kreidenweis, Sonia, advisor; DeMott, Paul, advisor; Pierce, Jeffrey, committee member; Volckens, John, committee memberInsufficient knowledge regarding the sources and number concentrations of atmospheric ice nucleating particles (INP) leads to large uncertainties in understanding the interaction of aerosols with cloud processes, such as cloud life time and precipitation rates. An increasingly important source of aerosol in the United States is biomass burning, particularly in the form of prescribed burns and wildfires in the southeastern and western U.S., respectively. Prior field and laboratory observations have suggested that biomass burning can be a source of INP. However, emissions from biomass burning are complex, varying with combustion efficiency, fuel type, plume age and dilution. Thus, this potentially important source of INP is poorly characterized. This study utilizes measurements of INP from a diverse set of biomass burning events to better understand INP associated with biomass burning in the U.S. Prescribed burns in Georgia and Colorado, two Colorado wildfires and two laboratory burns were monitored for INP number concentrations (nINP) using the Colorado State University continuous-flow diffusion chamber (CFDC) to activate INP in the condensation/immersion freezing nucleation mode. Additional measurements included total particle number concentrations, number concentrations of particles with diameters larger than 500 nm, aerosol mass concentrations, carbon monoxide concentrations and chemically-speciated bulk aerosol filter samples. Additionally, activated INP were collected onto TEM grids downstream of the CFDC, isolating INP for single particle chemical and morphological analyses. These fires varied by fuel type, including wiregrass, longleaf pine and ponderosa pine, and also varied by combustion efficiency, ranging from highly flaming to a mixture of flaming and smoldering. Additionally, plume histories were different between the fires including aged plumes from the wildfires and freshly emitted smoke from the prescribed and laboratory burns. The relationship between nINP and total particle number concentrations, evident within prescribed burning plumes, was degraded within aged smoke plumes from the wildfires, limiting the utility of this relationship for comparing laboratory and field data. Larger particles, represented by n500nm, are less vulnerable to plume processing and have previously been evaluated for their relation to nINP. Our measurements indicated that for a given n500nm, nINP associated with the wildfires were nearly an order of magnitude higher than nINP found in prescribed fire emissions. That is, nINP represented a much larger fraction of n500nm in wildfires as compared with prescribed fires. Further, an existing parameterization for "global" nINP that relates INP abundance to n500nm largely under-predicted and over-predicted nINP emitted from wildfires and prescribed burns, respectively. Reasons for the differences between INP characteristics in these emissions were explored, including variations in combustion efficiency, fuel type, transport time and environmental conditions. Combustion efficiency and fuel type were eliminated as controlling factors by comparing samples with contrasting combustion efficiencies and fuel types. Transport time was eliminated because the expected impact would be to reduce n500nm, thus resulting in the opposite effect from the observed change. Bulk aerosol chemical composition analyses support the potential role of elevated soil dust particle concentrations during the fires, contributing to the population of INP, but the bulk analyses do not target INP composition directly. Predictions from the Naval Aerosol Analysis and Prediction System model further indicate elevated dust mass concentrations during the wildfire periods, suggesting impact of mineral dust from long-range transport (LRT). It is hypothesized that both hardwood burning and soil lofting are responsible for the elevated production of INP in the Colorado wildfires in addition to LRT of mineral dust. The chemical compositions of INP were probed directly via TEM imaging. Single particle analyses of residual INP showed that they comprised various C-containing particle types, but with a higher abundance of mineral and metal oxide containing INP in emissions from flaming phase combustion. Fractal soot was found as an INP type comprising up to 60% of collected INP in young smoke emissions from the Georgia prescribed burns. In a series of laboratory combustion experiments, the use of a new instrumental set up, pairing the CFDC with a single particle soot photometer, revealed up to a 60% decrease in active INP after the removal of refractory black carbon from smoke aerosol emitted from a highly flaming burn of wiregrass, supporting that soot particles serve as INP in fire emissions. The presence of soil minerals was clearly evident in TEM images of samples taken during the wildfires in addition to tarballs, carbon balls most commonly associated with aged smoke plumes. These results demonstrate that the ice nucleating particles observed in the wildfires were influenced by other factors not represented in the smoke emitted from the laboratory or prescribed burns. Finally, an INP parameterization was developed based on the temperature dependent relationship between nINP and n500nm, following methods used by previous studies. This parameterization is likely only representative of the Hewlett and High Park wildfires due to the apparent impact of non-biomass-burning aerosol. However, all wildfires are typically associated with vigorous localized convection and arid soils, required for the lofting of the soils and dusts similar to these wildfires. It will be useful to compare future wildfires in various regions to the proposed parameterization.Item Open Access Characterizing the influence of anthropogenic emissions and transport variability on sulfate aerosol concentrations at Mauna Loa Observatory(Colorado State University. Libraries, 2013) Potter, Lauren E., author; Kreidenweis, Sonia, advisor; Maloney, Eric, committee member; Farmer, Delphine, committee member; Cooley, Daniel, committee memberSulfate aerosol in the atmosphere has substantial impacts on human health and environmental quality. Most notably, atmospheric sulfate has the potential to modify the earth's climate system through both direct and indirect radiative forcing mechanisms (Meehl et al., 2007). Emissions of sulfur dioxide, the primary precursor of sulfate aerosol, are now globally dominated by anthropogenic sources as a result of widespread fossil fuel combustion. Economic development in Asian countries since 1990 has contributed considerably to atmospheric sulfur loading, particularly China, which currently emits approximately 1/3 of global anthropogenic SO2 (Klimont et al., 2013). Observational and modeling studies have confirmed that anthropogenic pollutants from Asian sources can be transported long distances with important implications for future air quality and global climate change. Located in the remote Pacific Ocean (19.54Ā°N, 155.58Ā°W) at an elevation of 3.4 kilometers above sea level, Mauna Loa Observatory (MLO) is an ideal measurement site for ground-based, free tropospheric observations and is well situated to experience influence from springtime Asian outflow. This study makes use of a 14-year data set of aerosol ionic composition, obtained at MLO by the University of Hawaii at Manoa. Daily filter samples of total aerosol concentrations were made during nighttime downslope (free-tropospheric) transport conditions, from 1995 to 2008, and were analyzed for aerosol-phase concentrations of the following species: nitrate (NO3-), sulfate (SO42-), methanesulfonate (MSA), chloride (Cl-), oxalate, sodium (Na+), ammonium (NH4+), potassium (K+), magnesium (Mg2+), and calcium (Ca2+). An understanding of the factors controlling seasonal and interannual variations in aerosol speciation and concentrations at this site is complicated by the relatively short lifetimes of aerosols, compared with greenhouse gases which have also been sampled over long time periods at MLO. Aerosol filter data were supplemented with observations of gaseous radon (Rn222) and carbon monoxide (CO), used as tracers of long distance continental influence. Our study applied trajectory analysis and multiple linear regression to interpret the relative roles of aerosol precursor emissions and large-scale transport characteristics on observed MLO sulfate aerosol variability. We conclude that observed sulfate aerosol at MLO likely originated from a combination of anthropogenic, volcanic, and biogenic sources that varied seasonally and from year to year. Analysis of chemical continental tracer concentrations and HYSPLIT back trajectories suggests that non-negligible long distance influence from either the Asian or North American continents can be detected at MLO during all seasons although large interannual variability was observed. Possible influence of circulation changes in the Pacific Basin related to the El NiƱo-Southern Oscillation were found to be both species and seasonally dependent. We further found an increasing trend in monthly mean sulfate aerosol concentrations at MLO of 4.8% (7.3 ng m-3) per year during 1995-2008, significant at the 95% confidence level. Multiple linear regression results suggest that the observed trend in sulfate concentrations at MLO cannot reasonably be explained by variations in meteorology and transport efficiency alone. An increasing sulfate trend of 5.8 ng m-3 per year, statistically significant at the 90% confidence level, was found to be associated with the variable representing East Asian SO2 emissions. The results of this study provide evidence that MLO sulfate aerosol observations during 1995-2008 reflect, in part, recent trends in anthropogenic SO2 emissions which are superimposed onto the natural meteorological variability affecting transport efficiency.Item Unknown Constraining marine ice nucleating particle parameterizations in atmospheric models using observations from the Southern Ocean(Colorado State University. Libraries, 2020) Moore, Kathryn A., author; Kreidenweis, Sonia, advisor; DeMott, Paul, advisor; Farmer, Delphine, committee member; Pierce, Jeffrey, committee memberThe limited anthropogenic and terrestrial aerosol sources impacting the Southern Ocean (SO) make it a unique site to study the production of primary sea spray aerosols (SSA) and their role in modifying cloud properties. Previous observations of low ice nucleating particle (INP) concentrations and recent modeling work support the idea that the SO INP population is dominated by SSA. These marine INPs are hypothesized to strongly influence the lifetime, formation, and optical properties of the supercooled and mixed phase clouds that are common in the region, though direct observational evidence for this is lacking. This study focuses on improving our understanding of INP emissions in the marine boundary layer over the SO, with applicability to other ocean regions, and to provide in situ measurements with which to validate and improve INP parameterizations in global and cloud resolving models. Measurements of INPs and aerosols in the marine boundary layer were made during the Clouds, Aerosols, Precipitation Radiation and atmospherIc Composition Over the southeRN ocean 2 (CAPRICORN-2) study on the R/V Investigator during Jan. - March 2018. An initial focus of this thesis was on increasing speed and reproducibility of processing online INP measurements, as well as improving the determination of statistical significance and uncertainty bounds. Different approaches to parameterizing INPs in models are explored for SO aerosols, including the use of aerosol surface area and number concentrations. With an eye towards augmenting global datasets of INPs, a comparison of particle surface area measurements from four different techniques is presented, for use in developing and testing INP parameterizations for different sources and atmospheric conditions. Surface area concentrations derived from Wideband Integrated Bioaerosol Sensor (WIBS) and nephelometer observations are strongly correlated with direct particle size distribution measurements, and can be used in their stead. Uncertainty bounds for both techniques and a scaling factor for WIBS measurements are provided to aid in these estimates. INP concentrations observed during CAPRICORN-2 are very low across the entire temperature range measured (to -30 Ā°C), even compared to previous measurements of marine-dominated airmasses. Unlike INPs from other sources, Southern Ocean marine INPs appear most correlated with accumulation, rather than coarse mode, particles, and are dominated by submicron particles. Commonly used relationships between coarse mode particle number and total aerosol surface area show no significant correlation with SO INP concentrations, indicating a different functional form or different independent variable may be needed to accurately parameterize marine INPs in models.Item Unknown Fire and ice: analyzing ice nucleating particle emissions from western U.S. wildfires(Colorado State University. Libraries, 2019) Barry, Kevin Robert, author; Kreidenweis, Sonia, advisor; DeMott, Paul, advisor; Barnes, Elizabeth, committee member; Farmer, Delphine, committee memberWildfires in the western U.S. can have impacts on health and air quality and are forecasted to increase in the future. Some of the particles released from wildfires can affect cloud formation through serving as ice nucleating particles (INPs). INPs are necessary for heterogenous ice formation in mixed-phase clouds at temperatures warmer than about -38 Ā°C and can have climate implications from radiative impacts on cloud phase and by affecting cloud lifetime. Wildfires have been shown to be a potential source of INPs from previous ground-based measurement studies, but almost no data exist at the free tropospheric level that is relevant for cloud formation. The Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN) campaign that was conducted in summer 2018 utilized the NSF/NCAR C-130 to sample many smoke plumes of various ages in the free troposphere and aged smoke in the boundary layer. INP measurements were made with the CSU Continuous Flow Diffusion Chamber (CFDC) and with aerosol filter collections to analyze offline with the CSU Ice Spectrometer (IS). The results presented in this thesis indicate a contribution of smoke to the INP number concentration budget over the plume-background air, but much variability exists in concentrations and in INP composition among fires. Treatments of the filter suspensions show a dominant organic influence in all plume filters analyzed while a biological INP population is evident in several cases. For the South Sugarloaf fire, which had a primary fuel of sagebrush shrubland, the highest INP concentrations of the campaign were measured, and the unique INP temperature spectrum suggests lofting of material from uncombusted plant material. Normalization of INP concentrations measured in WE-CAN confirms that smoke is not an especially efficient source of ice nucleating particles, however emissions impacts may still occur regionally. The determination of a Normalized Excess Mixing Ratio (NEMR) of INP emissions for the first time will permit modeling of such impacts, and possible INP in-plume production will be explored in future research.Item Unknown Ice nucleating particles in the Arctic: measurement and source tracking(Colorado State University. Libraries, 2024) Barry, Kevin Robert, author; Kreidenweis, Sonia, advisor; DeMott, Paul, advisor; van den Heever, Susan, committee member; Fischer, Emily, committee member; Trivedi, Pankaj, committee memberThe Arctic landscape is rapidly changing in a warming climate, with sea ice melting and permafrost thawing. Its near-surface air temperature is warming 3.8 times faster than other regions around the world. This rapid warming is known as Arctic amplification. Clouds contribute to this amplification, with their presence and phase is important for determining the surface energy budget. Arctic mixed-phase clouds can last for several days but are not represented well in climate models. Special aerosols, called ice nucleating particles (INPs) trigger ice formation in the atmosphere at temperatures warmer than -38 Ā°C, and thus are important for determining the initiation, lifetime, and radiative properties of these clouds. Observations of INPs, especially over the central Arctic, are limited, and many sources are unknown. This dissertation has the overarching goal of increasing understanding of Arctic INPs. This is achieved through first presenting a full year of INP measurements in the central Arctic, as well as a full year of their composition, using coincident sampling of bacteria and fungi to gain insight into airmass origin. Next, some of the potentially most active Arctic INP sources are explored. Permafrost, which was known previously to contain high levels of INPs, was tested for its activity and persistence in water, and ability to be aerosolized through bubble bursting over several weeks. Then, sources of INPs were surveyed in a region that is controlled by permafrost (a thermokarst landscape). This included field measurements of permafrost, vegetation, sediment, active layer soil, water, and aerosol samples. A high temperature heat test was developed as a diagnostic tool to differentiate sources. Coincidentally, clean working methods to measure INPs were optimized, as efforts to reduce contamination are needed to accurately sample in this region. The main findings from this work suggest a regionally relatively homogenous population of Arctic INPs at most times of year, which is encouraging for efforts to represent them in numerical models across scales and understand their changes in the future. Permafrost-sourced INPs showed high activity and were enhanced near the coast. Unexpectedly, other components of the thermokarst landscape were found to be rich, organic INP reservoirs, emphasizing that the Arctic tundra is a diverse collection of potential contributors to the aerosol.Item Unknown Making real time measurements of ice nuclei concentrations at upper tropospheric temperatures: extending the capabilities of the continuous flow diffusion chamber(Colorado State University. Libraries, 2009) Richardson, Mathews, author; Kreidenweis, Sonia, advisorDue to their ubiquity, cirrus clouds are important drivers of climate. Researchers have developed a parameterization that predicts the onset of homogeneous freezing for particles of varying chemical composition. This parameterization is widely used to model cold cloud formation, but the applicability of this parameterization to real atmospheric aerosol has yet to be determined. The field-ready version of Colorado State University's continuous-flow diffusion chamber (CFDC-1H) is one of the few instruments capable of measuring atmospheric ice nuclei concentrations in real time. In this study, we examined the operational limits of the CFDC-1H at low temperature through a series of controlled laboratory studies using (NH 4)2SO4 particles at different operating conditions. We found that residence time played a dominant role in the CFDC-1H's ability to detect the onset of freezing at conditions closer to those predicted. Numerical studies confirmed this and indicated that at warmer temperatures the inability of the CFDC-1H to observe freezing onset conditions as predicted was attributable to the inability of particles to dilute rapidly enough while at colder temperatures the limited availability of water vapor in conjunction with limited residence times inhibited cloud particle growth. The final portion of this study focused on measurements of the freezing onset conditions of an ambient aerosol. Using water uptake measurements, we found that the hygroscopicity (Īŗ) of the ambient aerosol (0.1 to 0.2) was significantly lower than that of ammonium sulfate (0.6). However, as predicted by theory, there was no observably significant difference between the onset conditions of size-selected (NH4)2SO4 and size-selected ambient aerosol. Freezing activation curves for the total ambient aerosol indicated that size plays an important role in the fraction freezing and should be considered when making conclusions regarding chemical composition as a function of fraction freezing. The chemical composition of ice crystal residuals was dominated by mineral type elements and carbon containing particles, contrary to expectations. Further work is necessary for any conclusive statement regarding the chemical composition of the freezing nuclei.Item Unknown Measurement of low-altitude aerosol layers surrounding convective cold pool passage observed by uncrewed aircraft(Colorado State University. Libraries, 2024) Heffernan, Brian, author; Kreidenweis, Sonia, advisor; Perkins, Russell, advisor; Pierce, Jeffrey, committee member; Jathar, Shantanu, committee memberConvectively generated cold pools can have myriad impacts on local aerosol concentrations. Passage of cold pools may loft dust, pollen or other aerosols from the surface, and precipitation and humidity changes accompanying cold pools also impact local aerosols in several ways. The vertical profile of aerosols can have important effects on meteorology, however, the effects of cold pools on the vertical distribution of aerosol are largely unstudied. During the BioAerosol and Convective Storms (BACS) field campaigns in the Colorado plains in spring of 2022 and 2023, Uncrewed Aircraft (UA) were utilized to observe the vertical profile of aerosol, and how this vertical profile may be affected by the passage of cold pools. UAs with mounted aerosol and meteorological instrument packages were deployed in a vertical column to profile different atmospheric variables. Flights were conducted before, during, and after the passage of cold pools, and UA data were contextualized using radiosonde measurements and surface-based aerosol and meteorological instruments. A discussion of the challenges of UA-mounted aerosol sampling is presented. Validation experiments were conducted to assess the reliability of UA-mounted Optical Particle Counters (OPCs), and analyzed to show that UA-mounted OPCs can provide reliable data under certain circumstances. Two primary issues are discussed in detail: sensor drift and suppressed OPC sampling flow. A calibration procedure was developed and utilized to address the issue of sensor drift, while suppressed OPC sample flow was addressed by removing all data below a determined critical threshold flow rate. These methodologies lead to the creation of a robust data product for the measurement of aerosol vertical profiles using UA-mounted OPCs. Using these OPC data, an analysis of the vertical profiles observed during the BACS campaign is provided, up to 350m above the surface. We find that a common feature of a post cold pool environment is a layer of enhanced submicron aerosol concentration measured 120m above the surface. This feature and its evolution are examined in detail for several case studies, and different possible explanations are presented. Potential causes of this observed feature include pollen-rupture, low temperature inversions trapping aerosol in a low stable layer of elevated aerosol concentration, and emission and/or deposition of aerosols, but these explanations each appear to be insufficient. This feature appears to be caused by the dynamics of the cold pool, which can entrain and redistribute airmasses from different levels of the atmosphere.Item Open Access Metro West Middle College pilot program: an embedded case study(Colorado State University. Libraries, 2008) Huffman, Arlie C., III, author; Harbour, Clifford P., advisor; Kreidenweis, Sonia, advisorIn the early 1970's, a cooperative educational concept known as middle college was started to help underachieving and disenfranchised New York City public school students understand that college is an attainable goal. In 2004, the Career and Technical Education high school in Harris County Public School district, Harris Tech, and Metro West Community College (MWCC), all pseudonyms, joined to create their own middle college focusing on Career and Technical Education students. This pilot project, known as Metro West Middle College (MWMC), operated with the goals of helping students transition between secondary and postsecondary institutions, and increasing the level of collaboration between the two agencies. This research used an embedded case study qualitative methodology to investigate the levels of success of these goals. Three cases were embedded in the overall case study of MWMC. The first case consisted of state and district level administrators who were interviewed regarding statutes and policies that affected the operation of middle colleges. Administrators and faculty members from both Harris Tech and MWCC were surveyed in the second embedded case to provide the institutional context to the project. The third case was comprised of students who enrolled in MWMC during the first year of operation and parents of students who enrolled during the first two years. Data were compared to a set of six design principles developed by the Middle College National Consortium in 2005. The MWCC project planners addressed all of the design principles in general, but the data collected in this study showed that several key elements were missing. As a result, my research concluded that state-level middle college funding mechanisms were missing or contradictory, the program mission and goals were not clearly formulated and thus were not well communicated, collaborative program governance strategies were not used, the student selection process was not explicitly defined, and a formalized, ongoing student support structure was not provided. While these missing pieces had a deleterious effect on the overall success of the program, levels of student success were generally high, and most stakeholders reported a strong desire to continue developing this type of program.Item Open Access Nationwide decadal source apportionment of PM2.5 with a focus on iron(Colorado State University. Libraries, 2021) NiƱo, Lance, author; Kreidenweis, Sonia, advisor; Barnes, Elizabeth, committee member; Bond, Tami, committee memberFine particulate matter pollution (PM2.5) has detrimental effects on human health, visibility, and the environment. One component of PM2.5, aerosol-phase iron, also has a multi-faceted effect on climate. In its largely insoluble iron oxide form, found in dust aerosol, it absorbs shortwave radiation. Emissions from anthropogenic processes, primarily industry and coal combustion, also contain iron, with most of that iron in soluble forms. Soluble iron is an important phytoplankton nutrient and thus its atmospheric abundance is intertwined with carbon sequestration. To ascertain the various sources of PM2.5 as well as aerosol-phase iron across the contiguous United States, we used the ME-2 version of PMF to obtain a 10-factor source apportionment solution using IMPROVE data from 2011-2019. The percentage of anthropogenic iron at various sites during that time span varied from nearly none in the inter-mountain West to over 50% over the eastern half of the US. The percentage of total iron detected that was classified as soluble iron reached over 20% along coastal sites but was only around 3% of the total iron emitted. Trends in PM2.5 component factors showed a pronounced decrease in PM2.5 from coal combustion and various industrial sources during the time period, but trends were mixed and not significant for other sources. Further research is needed applying source apportionment to nationwide speciated datasets like IMPROVE, and a more comprehensive global PM2.5 observation network would enable source apportionment on a global scale.