Mountain Scholar :: Browsing by Author "Kreidenweis, Sonia M., committee member"

Browsing by Author "Kreidenweis, Sonia M., committee member"

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Open Access
Air toxic assessment for short-term ambient air pilot study at private house in Battlement Mesa near oil and gas drilling site
(Colorado State University. Libraries, 2011) Alhaji, Hussain, author; Reynolds, Stephen J., advisor; Brazile, William Joseph, committee member; Kreidenweis, Sonia M., committee member
This pilot study evaluated the ambient air concentrations in Battlement Mesa, Colorado at private house near a well pad, for the four-day period of February 7 through February 10 of 2011. The natural gas site was operating in the production phase of oil and gas development process, and there were 12 wells commercial line. The overlying purpose of the study was to provide preliminary evaluation of air quality characteristics within Battlement Mesa with particular attention to Speciated Non-Methane Organic Compounds/Volatile Organic Compounds (SNMOC/VOCs), fine particulate matter (PM2.5) and total volatile organic compounds (TVOC's). SNMOCs including benzene, toluene, ethylbenezene, and xylene (BTEX) compounds were collected and analyzed using a modified EPA Organic Compendium Method TO-12 over a 22-hour period using Summa-polished stainless steel canisters. PM2.5 levels were measured using a directing reading photometer, a Personal Data RAM (pDR-1200) for 24-hour sampling period. Total VOCs, were measured in real-time using a Rae Systems PPB Rae 3000 photo ionization detector (PID). To measure the meteorological data, a portable weather station was deployed at the fire station site (FR) during the sampling period (about half mile from the sampling location). Sampling was performed at two locations around the private house, and background samples were collected at the FR for each parameter. The large percentage of detection (high prevalence i.e. ~95%) in samples from all sites appears to indicate that local VOCs sources do have impacts on air pollution levels. Compounds that were detected in the highest concentrations were light alkanes (i.e. ethane, propane) and the BTEX group (benzene, toluene, ethylbenzene and xylenes). The BTEX group, benzene in particular, recorded a potential health risk compared to the Risk Based Concentration (RBC) developed by the Environmental Protection Agency (EPA). In general, the SNMOCs/VOCs levels detected were low for all samples. TVOCs levels were also low and are consistent with the BTEX group where the background site recoded higher levels than the sampling sites (Upstream "UP" and Downstream "DN" sites). No exceedances of Federal National Ambient Air Quality Standards were recorded for PM2.5. In addition, PM2.5 concentrations were generally highest in the UP site which is close to the well pad. Comparisons of PM2.5 data to data from other studies in Garfield County show that PM2.5 concentrations in Battlement Mesa (oil and gas development area) are similar to or higher than the Rifle area (urban area) Meteorological monitoring was performed on a continuous basis with one-hour averages being generated. Wind speed and precipitation (snow) are the most pronounced meteorological parameters that are correlated with VOCs and PM2.5 levels. Overall for the study, pollutant levels were found to be generally very low as compared to the standards and suggested guidelines. In some locations, it is likely that more elevated pollutant levels are the result of local or individual sources. BTEX emissions sources should be evaluated more thoroughly and benzene in particular since elevated levels were observed. Given that benzene recorded a potential health hazard in the area (exceeded lower level for cancer risk), it is recommended that a comprehensive air study that measures VOCs at different seasons and at other well-development processes be conducted. The background site (FR) is affected by several emission sources. Therefore, it is recommended to relocate the background site to have a better representative background. A direct reading photometer method using the Personal Data RAM (pDR1200) is not the best method to collect the particulates during the winter season due to instrument related temperature bias. Therefore, an alternative method to measure the particulate matter is advised.
Open Access
Aqueous atmospheric organic processing: effects of fog and cloud composition
(Colorado State University. Libraries, 2016) Boris, Alexandra Jeanne, author; Collett, Jeffrey L., advisor; Farmer, Delphine K., committee member; Kreidenweis, Sonia M., committee member; Pierce, Jeffrey R., committee member
Cloud and fog droplets are well-suited venues for organic reactions leading to the formation of suspended particulate matter in the atmosphere. Suspended particulate matter formed through aqueous reactions is called "aqueous secondary organic aerosol" or aqSOA, and can interact with solar radiation and adversely impact human and ecosystem health. Although atmospheric observations and lab simulations have verified the formation of aqSOA, little is known about where and when it occurs in the atmosphere. The organic (carbonaceous) reactions leading to aqSOA formation also degrade chemicals in the atmosphere, impacting the potential health effects of fog water deposited to ecosystems and crops. In the present work, studies are described that approach these aqueous oxidation reactions from field and lab perspectives, capturing both complex and simple experiments. Some results will be presented that capture the dynamics of aqSOA formation from studies of in-situ fog chemistry, but the lack of control over environmental variables in these observations will be highlighted. Lab-based reactions of fog and cloud water will also be presented, which oppositely underscore the missing variables in such simplified lab experiments. Despite the need for more advanced experimental design to quantify aqSOA formation and identify its sensitivities to real atmospheric variables, these field and lab approaches have garnered new insight into some key aspects of aqueous oxidation. Fog at Baengnyeong Island (BYI) in the Yellow Sea of Korea was collected in July 2014. Fog chemistry was exemplary of aged atmospheric components: sulfur was almost entirely oxidized (98.9 to 99.8% was present as S(VI) versus S(IV)), and peroxides, which can serve as oxidants, were depleted. Organic acids at times accounted for >50% of the total organic carbon (TOC) by carbon mass, indicating that organic matter was highly oxidized. Although formic and acetic acids were the most abundant, concentrations of ten out of the 18 organic acids quantified were above 1 μM. Some organic sulfur and organic nitrogen species were additionally observed, which may have formed during aqueous reactions in the fog or in humid conditions as air traveled to BYI. Back trajectories demonstrated that the relative humidities of the air masses arriving at BYI were typically >80%, suggesting that oxidation could have taken place in the aqueous phase. The Southern California coast is frequently foggy during the summer months, but in contrast to BYI, is closer to many atmospheric chemical emissions sources. Fog water was collected at Casitas Pass (CP) near Ventura, California in June 2015. Regional oil drilling and/or refinery emissions influenced the composition of foggy air, as did biogenic and marine emissions. Only 20% of TOC on average was contributed by organic acids, suggesting influence of fresher organic emissions than observed at BYI. After 3-5 hours of foggy conditions, however, organic sulfur and organic nitrogen species were observed, suggesting possible in-fog oxidation. A contrast between the 2015 study and a 1985/6 study demonstrated improved air quality compared to 1985/6, with lower concentrations of anthropogenically derived species (NH4+, NO3-, SO42-, acetate, formate, and formaldehyde), but similar concentrations of naturally derived species (Na+, Cl-, Ca2+, and Mg2+). Lab work involving aqueous oxidation within real cloud water revealed that organic constituents of cloud water caused oxidation reactions to slow due to competition for oxidant. Inorganic species (NH4+, SO42- and NO3-) at concentrations relevant to polluted cloud water did not have a statistically significant effect on oxidation. Mechanisms of oxidation were also surprisingly unaffected by cloud water components: similar low molecular mass organic acids were observed as products of oxidation in pure and cloud water. Oxidation of real cloud water sample constituents in the lab revealed that organosulfate species were produced when sufficient SO42- and organic species concentrations were present. Four fog and cloud water samples were oxidized, demonstrating different oxidation regimes: a BYI fog was clearly more aged such that organosulfate esters were formed; cloud water from Mount Tai, China contained biomass burning and anthropogenic aromatic emissions and produced organic acids similar to those observed from nitrophenol chemical standard oxidations; and fog water from CP containing fresher emissions produced mainly low molecular mass organic acids. The aqueous oxidation of biomass burning emissions collected using a mist chamber resulted in the formation of a variety of low molecular mass organic acids. No apparent structure-activity relationship was observed: aliphatic and aromatic species were oxidized at similar rates when exposed to OH radicals. The degradation of potentially toxic organic nitrogen species as well as net production of semi-volatile organic acid products were observed, demonstrating that in-cloud oxidation of biomass burning emissions likely contributes to the chemical evolution and organic aerosol mass within smoke plumes. Overall, there is still a need for advanced experiment development in the field of aqueous organic atmospheric chemistry. The finding that physical processes obscured effects of aqueous reactions during fog field studies should, likewise, guide future field work toward the concurrent measurement of microphysical parameters and possible development of higher efficiency techniques for droplet collection and/or real-time chemical analyses. However, the combination of bulk reactions and fog studies employed within this thesis has allowed the effects of real fog and cloud water chemistry on aqSOA formation to be demonstrated. The common oxidation products identified under most aqueous atmospheric regimes, including low molecular mass organic acid species, but specific environmental requirements for other products such as organosulfates, should guide future research in identifying molecular tracers of aqSOA and sensitivity studies of aqSOA formation to environmental factors.
Open Access
Aqueous phase sulfate production in clouds at Mt. Tai in eastern China
(Colorado State University. Libraries, 2011) Shen, Xinhua, author; Collett, Jeffrey L., advisor; Kreidenweis, Sonia M., committee member; Rutledge, Steven A., committee member; Reynolds, Stephen J., committee member
Clouds play an important role in the oxidation of sulfur dioxide to sulfate, since aqueous phase sulfur dioxide oxidation is typically much faster than oxidation in the gas phase. Important aqueous phase oxidants include hydrogen peroxide, ozone and oxygen (catalyzed by trace metals). Because quantities of emitted sulfur dioxide in China are so large, however, it is possible that they exceed the capacity of regional clouds for sulfate production, leading to enhanced long-range transport of emitted SO2 and its oxidation product, sulfate. In order to assess the ability of regional clouds to support aqueous sulfur oxidation, four field campaigns were conducted in 2007 and 2008 at Mt. Tai in eastern China. Single and 2-stage Caltech Active Strand Cloudwater Collectors were used to collect bulk and drop size-resolved cloudwater samples, respectively. Key species that determine aqueous phase sulfur oxidation were analyzed, including cloudwater pH, S(IV), H2O2, Fe, and Mn. Gas phase SO2, O3, and H2O2 were also measured continuously during the campaigns. Other species in cloudwater, including inorganic ions, total organic carbon (TOC), formaldehyde, and organic acids were also analyzed to provide a fuller view of cloud chemistry in the region. Numerous periods of cloud interception/fog occurred during the four Mt. Tai field campaigns; more than 500 cloudwater samples were collected in total. A wide range of cloud pH values was observed, from 2.6 to 7.6. SO42-, NO3-, and NH4+ were the major inorganic species for all four campaigns. TOC concentrations were also very high in some samples (up to 200 ppmC), especially when clouds were impacted by emissions from agricultural biomass burning. Back-trajectory analysis also indicated influence by dust transport from northern China in a few spring cloud events. Differences between the compositions of small and large cloud droplets were observed, but generally found to be modest for major solute species and pH. Mt. Tai clouds were found to interact strongly with PM2.5 sulfate, nitrate, and ammonium with average scavenging efficiencies of 80%, 75%, and 78%, respectively, across 7 events studied. Scavenging efficiencies for total sulfur (PM2.5 sulfate plus gaseous sulfur dioxide), however, averaged only 43%, indicating the majority of gaseous sulfur dioxide remained unprocessed in these cloud events. H2O2 was found to be the most important oxidant for aqueous sulfate production 68% of the time. High concentrations of residual H2O2 were measured in some samples, especially during summertime, implying a substantial capacity for additional sulfur oxidation. The importance of ozone as a S(IV) oxidant increased substantially as cloud pH climbed above pH 5 to 5.3. Overall, ozone was found to be the most important aqueous S(IV) oxidant in 21% of the sampling periods. Trace metal-catalyzed S(IV) autooxidation was determined to be the fastest aqueous sulfate production pathway in the remaining 11% of the cases. Complexation with formaldehyde was also found to be a potentially important fate for aqueous S(IV) and should be examined in more detail in future studies. Observed chemical heterogeneity among cloud drop populations was predicted to enhance rates of S(IV) oxidation by ozone and enhance or slow metal-catalyzed S(IV) autooxidation rates in some periods. These effects were found to be only of minor importance, however, as H2O2 was the dominant S(IV) oxidant most of the time.
Open Access
Atmospheric and air quality implications of C2-C5 alkane emissions from the oil and gas sector
(Colorado State University. Libraries, 2018) Tzompa Sosa, Zitely Asafay, author; Fischer, Emily, advisor; Kreidenweis, Sonia M., committee member; Pierce, Jeffrey, committee member; Jathar, Shantanu, committee member
Emissions of C2-C5 alkanes from the U.S. oil and gas sector have changed rapidly over the last decade. This dissertation quantifies the role of the oil and gas sector on light alkane emissions and abundances at local, regional, and global scales. First, we present an updated global ethane (C2H6) emission inventory based on 2010 satellite-derived CH4 fluxes with adjusted C2H6 emissions over the U.S. from the National Emission Inventory (NEI 2011). We contrast our global 2010 C2H6 emission inventory with one developed for 2001. The C2H6 difference between global anthropogenic emissions is subtle (7.9 versus 7.2 Tg yr-1), but the spatial distribution of the emissions is distinct. In the 2010 C2H6 inventory, fossil fuel sources in the Northern Hemisphere represent half of global C2H6 emissions and 95% of global fossil fuel emissions. Over the U.S., un-adjusted NEI 2011 C2H6 emissions produce mixing ratios that are 14-50 % of those observed by aircraft observations (2008-2014). When the NEI 2011 C2H6 emission totals are scaled by a factor of 1.4, the GEOS-Chem model largely reproduces a regional suite of observations, with the exception of the central U.S., where it continues to under- predict observed mixing ratios in the lower troposphere. Second, we use a nested GEOS-Chem simulation driven by updated 2011NEI emissions with aircraft, surface and column observations to 1) document spatial patterns in the emissions and observed atmospheric abundances of C2-C5 alkanes over the U.S., and 2) estimate the contribution of emissions from the U.S. oil and gas industry to these patterns. The oil and gas sector in the updated 2011NEI contributes >80% of the total U.S. emissions of C2H6 and propane (C3H8), and emissions of these species are largest in the central U.S. Observed mixing ratios of C2-C5 alkanes show enhancements over the central U.S. below 2 km. A nested GEOS-Chem simulation underpredicts observed C3H8 mixing ratios in the boundary layer over several U.S. regions and the relative underprediction is not consistent, suggesting C3H8 emissions should receive more attention moving forward. Our decision to consider only C4-C5 alkane emissions as a single lumped species produces a geographic distribution similar to observations. Due to the increasing importance of oil and gas emissions in the U.S., we recommend continued support of existing long-term measurements of C2-C5 alkanes. We suggest additional monitoring of C2-C5 alkanes downwind of northeastern Colorado, Wyoming and western North Dakota to capture changes in these regions. The atmospheric chemistry modeling community should also evaluate whether chemical mechanisms that lump ≤ C6 alkanes are sufficient to understand air quality issues in regions with large emissions of these species. Finally, we investigate the contribution of C2-C5 alkane emissions from the U.S. oil and gas industry to O3 abundances at regional and global scales. Emissions of C2-C5 alkanes from the oil and gas sector make the largest contribution to ozone (O3) production over the central U.S. compared to other regions. The Colorado Front Range is the 8-hour O3 non-attainment area with the highest summertime daytime average O3 enhancement attributed to the U.S. oil and gas sector. The global tropospheric contribution of C2-C5 alkane emissions from the U.S. oil and gas sector to the O3 burden is 0.5 Tg for the year 2011, which represents 0.27% of the Northern Hemisphere tropospheric O3 burden.
Open Access
Atmospheric nitrogen and sulfur deposition in Rocky Mountain National Park
(Colorado State University. Libraries, 2008) Beem, Katherine B., author; Collett, Jeffrey L., advisor; Davis, Jessica G., committee member; Kreidenweis, Sonia M., committee member
Rocky Mountain National Park (RMNP) is experiencing a number of adverse effects due to atmospheric nitrogen (N) and sulfur (S) compounds. Airborne nitrate and sulfate particles contribute to visibility degradation in the park while nitrogen deposition is producing changes in ecosystem function and surface water chemistry. Both sulfur and nitrogen compounds are essential nutrients for life; however, some environments have naturally limited supplies of sulfur and nitrogen which restrict biological activity. Increasing the amounts of these compounds can be toxic, even life threatening, to the ecosystem. Concerns about increasing deposition are especially important in national parks where excess nitrogen and sulfur can upset the delicate balance between species of flora and fauna in prized natural ecosystems. Measurements were made during the Rocky Mountain Airborne Nitrogen and Sulfur (RoMANS) study to quantify both N and S wet and dry deposition and to determine the most important species and pathways contributing to N deposition. Gas and particle concentrations were measured and precipitation samples were collected to gain a better understanding of nitrogen and sulfur transport to and deposition in RMNP. Samples were collected at 12 sites across the state of Colorado in March and April 2006 and at 13 sites in north central Colorado in July and August 2006. Historical data suggest that these are the seasons when N deposition in RMNP is greatest. The majority of wet deposition in the spring was from a single, large upslope snowstorm, while in the summer wet deposition inputs were spread across many more events. Total wet deposition of N in the summer was larger than during spring. Ammonium was the largest contributor to both spring and summer wet deposition in the park, followed by nitrate. Organic nitrogen, which is not routinely measured, contributed an average of 616.39 μg N/m2/event in the spring and 847.2 μg N/m2/event in the summer at the core sampling site. These deposition amounts were 22% and 16%, respectively, of total wet nitrogen deposition at this site. Dry deposition in RMNP was dominated by gaseous species which feature higher deposition velocities than accumulation mode aerosol particles. Ammonia, which is not routinely measured, was the largest contributor to dry N deposition followed by nitric acid. Dry deposition of fine particle nitrate and ammonium made only small contributions to total N deposition. Total N inputs were dominated by wet processes during both spring and summer. Wet deposition of organic nitrogen and dry deposition of gaseous ammonia comprised the 3rd and 4th largest contributions to the total N deposition budget. Together these pathways contributed nearly one-third of total measured N deposition, suggesting they should be examined more closely in assessing nitrogen impacts on national park ecosystems.
Open Access
Baseline evaluation of indoor air quality from Nicaraguan households using traditional cook stoves
(Colorado State University. Libraries, 2010) Bazemore, Heather, author; Reynolds, Stephen J., advisor; Peel, Jennifer L., advisor; Kreidenweis, Sonia M., committee member
Indoor cook stoves are still used as a primary energy source across the world in many developing countries. Inefficient stoves cause incomplete combustion of biomass fuel, resulting in an unhealthy increase of indoor air pollutants, including carbon monoxide (CO) and particle matter (PM). Use of these stoves is a global problem that must be addressed to help reduce indoor air pollutant exposures and combustion emissions. Most studies assessing traditional cook stoves are limited; the extended length and thorough exposure assessment of this study make it unique, providing better data for evaluation. This part of the study will assess the baseline exposure data from a longitudinal study of 123 Nicaraguan households collected over the summer of 2008. Fine particulate matter (PM2.5) was assessed continuously via 48-hour indoor monitoring using the UCB Particle Monitor. Indoor and personal carbon monoxide levels were assessed continuously via 48-hour indoor and personal monitoring using the lightweight, portable, data-logging Drager Pac 7000. PM2.5 and carbon monoxide indoor sampling devices were collocated inside the kitchen at a height representative of breathing zones. The personal carbon monoxide device was worn by the participant during the day and placed by her bedside overnight. Regression exposure models were developed using variables from the kitchen that can predict ventilation, including amount of eave space, kitchen volume, number of windows, number of doors, number of walls, and primary type of wall material. Cooking practices and activities were also considered in the models including exposure to environmental tobacco smoke, hours spent cooking per day, hours fire burns per day, and hours spent in the room with the fire burning per day. At the end of the summer baseline collection, improved cook stoves were installed in each participating household. High concentrations of indoor air pollution were recorded in households using traditional cook stoves. For indoor carbon monoxide, mean concentrations were 146 ppm (1-hour max), 67 ppm (8-hour max), and 26 ppm (48-hour). For personal CO, mean concentrations were 32 ppm (1-hour max), 8 ppm (8-hour max), and 2 ppm (48-hour). For indoor PM2.5, mean concentrations were 11,272 μg/m3 (1-hour max), 3655 μg/m3 (8-hour max), and 1364 μg/m3 (48-hour). In exposure assessment models, kitchen volume and exposure to environmental tobacco smoke were found to explain the most variation in indoor carbon monoxide levels. For personal carbon monoxide, number of doors and hours spent cooking per day influenced levels most. Amount of eave space and environmental tobacco smoke explained the most variation in indoor PM2.5 levels. Peaks in pollutant exposure were also evaluated in assessment models. However, all model results should be interpreted with caution. R-square values were very low for these models, meaning that the variables we collected data on did not explain much variation in pollutant concentrations. The data collected on exposure parameters did not explain much variation in indoor air quality. Further research is needed as to which housing factors and/or cooking practices affect pollutant levels most.
Open Access
Cavity enhanced instruments for detection of hydrogen chloride and aerosol optical extinction
(Colorado State University. Libraries, 2013) Franka, Isaiah S., author; Yalin, Azer P., advisor; Kreidenweis, Sonia M., committee member; Marchese, Anthony J., committee member
This thesis concerns the development of cavity enhanced instruments for atmospheric science studies. Hydrochloric acid (HCl) is an important reservoir species for active halogens which are thought to participate in cycles that deplete ozone. In order to understand these halogens and their effect on ozone depletion, a cavity ring-down spectroscopy (CRDS) based instrument was developed for ultra-sensitive HCl concentration measurements. The instrument has a (1σ) limit of detection of 10 pptv in 5 min and has high specificity to HCl. Aerosols are a fundamental contribution to Earth's radiation budget and represent one of the largest unconstrained unknowns in estimating climate change. The effect of aerosols on climate and air quality is closely tied to their spectral properties as well as particle chemical composition, size, and shape. Aerosol extinction coefficient (sum of light attenuation by scattering and absorption coefficients) is an important optical property for determining aerosol radiative forcing. A broadband cavity enhanced absorption spectroscopy (CEAS) laser-based instrument for measurement of aerosol extinction has been created with a minimum detectable extinction coefficient of 8x10-8 cm-1 for 10-ms collection time. This thesis details the development and validation of these cavity enhanced spectroscopy based instruments.
Open Access
Characteristics sources, and formation of organic aerosols in the central Rocky Mountains
(Colorado State University. Libraries, 2014) Schurman, Misha Iris, author; Collett, Jeffrey L., advisor; Kreidenweis, Sonia M., committee member; Henry, Charles S., committee member; Fischer, Emily V., committee member
To view the abstract, please see the full text of the document.
Open Access
Characterizing ammonia concentrations and deposition in the United States
(Colorado State University. Libraries, 2015) Li, Yi, author; Collett, Jeffrey L., advisor; Kreidenweis, Sonia M., committee member; Fischer, Emily, committee member; Ham, Jay, committee member
Rapid development of agricultural activities and fossil fuel combustion in the United States led to a great increase of reactive nitrogen (Nr) emissions in the second half of the twentieth century. These emissions have been linked to excess nitrogen (N) deposition in natural ecosystems through dry and wet deposition pathways that can lead to adverse environmental impacts. Furthermore, as precursors of ozone and fine particles, reactive nitrogen species impact regional air quality with resulting effects on human health, visibility, and climate forcing. In this dissertation, ambient concentrations of reactive nitrogen species and their deposition are examined in the Rocky Mountain region and across the country. Particular emphasis is placed on ammonia, a currently unregulated pollutant, despite its important contributions both to nitrogen deposition and fine particle formation. Continuous measurements of the atmospheric trace gases ammonia (NH3) and nitric acid (HNO3) and of fine particle (PM2.5) ammonium (NH4+), nitrate (NO3-) and sulfate (SO42-) were conducted using a denuder/filter system from December 2006 to December 2011 at Boulder, Wyoming, a region of active gas production. The average five year concentrations of NH3, HNO3, NH4+, NO3- and SO42- were 0.17, 0.19, 0.26, 0.32, and 0.48 µg/m3, respectively. Significant seasonal patterns were observed. The concentration of NH3 was higher in the summer than in other seasons, consistent with increased NH3 emissions and a shift in the ammonium nitrate (NH4NO3) equilibrium toward the gas phase at higher temperatures. High HNO3 concentrations were observed both in the summer and the winter. Elevated wintertime HNO3 production appeared to be due to active local photochemistry in a shallow boundary layer over a reflective, snow-covered surface. PM2.5 NH4+ and SO42- concentrations peaked in summer while NO3- concentrations peaked in winter. Cold winter temperatures drove the NH3-HNO3-NH4NO3 equilibrium toward particulate NH4NO3. A lack of NH3, however, frequently resulted in substantial residual gas phase HNO3 even under cold winter conditions. Concentrated agricultural activities and animal feeding operations in the northeastern plains of Colorado represent an important source of atmospheric NH3 that contributes to regional fine particle formation and to nitrogen deposition to sensitive ecosystems in Rocky Mountain National Park (RMNP) located ~80 km to the west. In order to better understand temporal and spatial differences in NH3 concentrations in this source region, weekly concentrations of NH3 were measured at 14 locations during the summers of 2010 to 2014 using Radiello passive NH3 samplers. Weekly average NH3 concentrations ranged from 2.8 µg/m3 to 41.3 µg/m3 with the highest concentrations near large concentrated animal feeding operations (CAFOs). The annual summertime mean NH3 concentrations were stable in this region from 2010 to 2014, providing a baseline against which concentration changes associated with future changes in regional NH3 emissions can be assessed. Vertical profiles of NH3 were also measured on the 300 m Boulder Atmospheric Observatory (BAO) tower throughout 2012. The highest NH3 concentration along the vertical profile was always observed at the 10 m height (annual average concentration is 4.63 µg/m3), decreasing toward the surface (4.35 µg/m3 at 1 m) and toward higher altitudes (1.93 µg/m3 at 300 m). Seasonal changes in the steepness of the vertical concentration gradient were observed, with the sharpest gradients in cooler seasons when thermal inversions restricted vertical mixing of surface-based emissions. The NH3 spatial distributions measured using the passive samplers are compared with NH3 columns retrieved by the Infrared Atmospheric Sounding Interferometer (IASI) satellite and concentrations simulated by the Comprehensive Air quality Model with extensions (CAMx), providing insight into the regional performance of each. U.S. efforts to reduce NOx emissions since the 1970s have substantially reduced nitrate deposition, as evidenced by strongly decreasing trends in long-term wet deposition data. These decreases in nitrate deposition along with increases in wet ammonium deposition have altered the balance between oxidized and reduced nitrogen deposition. Across most of the U.S., wet deposition has evolved from a nitrate dominated situation in the 1980s to an ammonium dominated situation in recent years. Recent measurements of gaseous NH3 concentrations across several regions of the U.S., along with longer-established measurements of gas phase nitric acid, fine particle ammonium and nitrate, and wet deposition of ammonium and nitrate, permit new insight into the balance of oxidized and reduced nitrogen in the total (wet + dry) U.S. reactive nitrogen deposition budget. Utilizing observations from 37 monitoring sites across the U.S., we estimate that reduced nitrogen contributes, on average, approximately 65 percent of the total inorganic N deposition budget. Dry NH3 deposition plays an especially key role in N deposition compared with other N deposition pathways, contributing from 19% to 65% in different regions. With reduced N species now dominating the wet and dry reactive N deposition budgets in much of the country and future estimates suggesting growing ammonia emissions, the U.S. will need to consider ways to actively reduce NH3 emissions if it is to continue progress toward reducing N deposition to sustainable levels defined by ecosystem critical loads.
Open Access
Cold pool train dynamics and transport
(Colorado State University. Libraries, 2023) Neumaier, Christine Allison, author; van den Heever, Susan C., advisor; Grant, Leah D., advisor; Kreidenweis, Sonia M., committee member; Venayagamoorthy, Subhas K., committee member
Convectively generated cold air outflows, referred to as cold pools, can initiate new convection and loft aerosols, such as dust or pollen. In the BioAerosols and Convective Storms Phase I (BACS-I) field campaign, we observed multiple cold pools passing over the same location on the same day, without colliding, which we refer to as a "cold pool train". The goals of this study are to examine how the dynamics of cold pools in a cold pool train differ, how cold pools in a cold pool train affect the vertical distribution of aerosols, and how the results may change if the properties of the second cold pool change. We utilize idealized simulations of a cold pool train composed of two cold pools to investigate the dynamics of the cold pools in the train and how cold pool trains loft and transport aerosols. We test the sensitivity of the second cold pool's evolution and aerosol lofting to its initial temperature deficit and timing relative to the first cold pool, based on the cold pool trains observed during BACS-I. Passive tracers are initialized at different times to represent the background aerosols present before cold pools, aerosols newly emitted after the passage of the first cold pool in the train, and aerosols within and ahead of each cold pool, to distinguish between how cold pools loft their own air compared to distinct environmental air. We find that the first cold pool (CP1) in the cold pool train stably stratifies the environment ahead of the downshear side of the second cold pool (CP2) in the train. All else equal, this stabilization acts to decrease the height of CP2's head and increase its propagation speed. However, the stratification also increases the horizontal wind shear ahead of CP2 by decreasing the lower level wind speeds, which opposes the stability effects and acts to deepen the head of CP2. In the CONTROL case, where CP2 is initialized two hours after CP1 and with the same temperature deficit as CP1, we find that the wind profile plays a more dominant role for the dynamics of CP2 because overall, CP2's head is deeper and propagates slower compared to CP1. In the temperature deficit sensitivity experiments, we find that CP2's head depth and propagation speed decreases with decreasing temperature deficit. Finally, in the timing sensitivity tests of CP2, we find CP2 initiated 90 minutes after CP1 had the deepest head, while CP2 in the CONTROL (120 minutes) experiment propagated the slowest. Our analysis of the tracer lofting mechanisms in the simulations shows that the downshear leading edge of CP1 lofts the highest concentration of background aerosol, while the downshear leading edge of the CONTROL CP2 lofts less than half of the amount of background aerosol as CP1. However, the downshear leading edge of CP2 lofts more than double the concentration of newly emitted aerosol compared to the background aerosol lofted by CP1. The atmospheric stratification left behind by CP1 acts to trap the newly emitted aerosol near the surface, leading to greater concentrations lofted compared to the background aerosol which is well mixed in the boundary layer. Analysis of the tracers initialized within and ahead of the cold pools demonstrates that the lofted aerosol primarily originates from the air ahead of the cold pools, while the aerosol originating in the cold pools remains trapped within the cold pools. The CONTROL CP2 lofts the most aerosol of the temperature deficit sensitivity tests, and the CONTROL CP2, released the farthest apart temporally from CP1, lofts the most aerosol out of the timing sensitivity tests. Therefore, while the wind profile change ahead of CP2 plays a dominant role in its dynamics, atmospheric static stabilization plays a dominant role for the aerosol concentration lofted by CP2.
Open Access
Environmental controls and aerosol impacts on tropical sea breeze convection
(Colorado State University. Libraries, 2020) Park, Jungmin, author; van den Heever, Susan C., advisor; Cooley, Daniel S., committee member; Kreidenweis, Sonia M., committee member; Miller, Steven D., committee member; Rasmussen, Kristen L., committee member
Nearly half of the world's human population resides within 150 km of the ocean, and this coastal population is expected to continue increasing over the next several decades. The accurate prediction of convection and its impacts on precipitation and air quality in coastal zones, both of which impact all life's health and safety in coastal regions, is becoming increasingly critical. Thermally driven sea breeze circulations are ubiquitous and serve to initiate and support the development of convection. Despite their importance, forecasting sea breeze convection remains very challenging due to the coexistence, covariance, and interactions of the thermodynamic, microphysical, aerosol, and surface properties of the littoral zone. Therefore, the overarching goal of this dissertation research is to enhance our understanding of the sensitivity of sea breeze circulation and associated convection to various environmental parameters and aerosol loading. More specifically, the objectives are the following: (1) to assess the relative importance of ten different environmental parameters previously identified as playing critical roles in tropical sea breeze convection; and (2) to examine how enhanced aerosol loading affects sea breeze convection through both microphysical and aerosol-radiation interactions, and how the environment modulates these effects. In the first study, the relative roles of five thermodynamic, one wind, and four land/ocean-surface properties in determining the structure and intensity of sea breeze convection are evaluated using ensemble cloud-resolving simulations combined with statistical emulation. The results demonstrate that the initial zonal wind speed and soil saturation fraction are the primary controls on the inland sea breeze propagation. Two distinct regimes of sea breeze-initiated convection, a shallow and a deep convective mode, are also identified. The convective intensity of the shallow mode is negatively correlated by the inversion strength, whereas the boundary layer potential temperature is the dominant control of the deep mode. The processes associated with these predominant controls are analyzed, and the results of this study underscore possible avenues for future improvements in numerical weather prediction of sea breeze convection. The sea breeze circulation and associated convection play an important role in the transport and processing of aerosol particles. However, the extent and magnitude of both direct and indirect aerosol effects on sea breeze convection are not well known. In the second part of this dissertation, the impacts of enhanced aerosol concentrations on sea breeze convection are examined. The results demonstrate that aerosol-radiation-land surface interactions produce less favorable environments for sea breeze convection through direct aerosol forcing. When aerosol-radiation interactions are eliminated, enhanced aerosol loading leads to stronger over-land updrafts in the warm-phase region of the clouds through increased condensational growth and latent heating. This process occurs irrespective of the sea breeze environment. While condensational invigoration of convective updrafts is therefore robust in the absence of aerosol direct effects, the cold-phase convective responses are found to be environmentally modulated, and updrafts may be stronger, weaker, or unchanged in the presence of enhanced aerosol loading. Surface precipitation responses to aerosol loading also appear to be modulated by aerosol-radiation interactions and the environment. In the absence of the aerosol direct effect, the impacts of enhanced aerosol loading may produce increased, decreased, or unchanged accumulated surface precipitation, depending on the environment in which the convection develops. However, when aerosols are allowed to interact with the radiation, a consistent reduction in surface precipitation with increasing aerosol loading is observed, although the environment once again modulated the magnitude of this aerosol-induced reduction.
Open Access
Estimating contributions of primary biomass combustion to fine particulate matter at sites in the western United States
(Colorado State University. Libraries, 2008) Holden, Amanda S., author; Collett, Jeffrey L., advisor; Henry, Charles S., committee member; Kreidenweis, Sonia M., committee member
Biomass combustion occurs throughout the world and has many implications for human health, air quality and visibility, and climate change. To better understand the impacts of biomass combustion in the western United States, six-day integrated fine particle samples were collected during the winter and summer seasons of 2004-2006 at seven IMPROVE sampling sites using Hi-Vol samplers. These sites included both urban and rural locations. Filter samples were analyzed for organic and elemental carbon, levoglucosan, and a suite of particulate ions. Levoglucosan, a thermal degradation product of cellulose, is a widely used tracer for primary biomass combustion. Measurements of levoglucosan and other carbohydrates were made using a new approach involving aqueous filter extraction followed by direct analysis using High Performance Anion Exchange Chromatography. In this method carbohydrates are separated on a Dionex Carbopac PA-10 column and detected using pulsed amperometry. Source profiles for primary biomass combustion were applied to each of these samples to estimate the contributions of carbon from both residential wood burning (during the winter seasons) and wildland fires (during the summer seasons). Wildland fire source profiles were determined from FLAME (Fire Lab at Missoula Experiment) campaigns at the USFS/USDA Fire Science Lab in Missoula, MT, during which fine particle samples were collected from source burns of approximately 30 fuel types. Residential wood combustion source profiles were collected from the literature. Primary biomass combustion contributions to contemporary PM2.5 carbon, determined separately from carbon isotope measurements at Lawrence Livermore National Laboratory, ranged from 0.4% to more than 100%. Contributions of primary biomass combustion were higher at rural sites, while urban sites showed greater contributions of fossil carbon. Primary biomass combustion contributed a larger fraction of total carbon in the summer at southern sites, while northern sites had larger contributions during the colder winter months.
Open Access
Examining the impacts of convective environments on storms using observations and numerical models
(Colorado State University. Libraries, 2022) Freeman, Sean William, author; van den Heever, Susan C., advisor; Bell, Michael M., committee member; Kreidenweis, Sonia M., committee member; Eykholt, Richard, committee member
Convective clouds are significant contributors to both weather and climate. While the basic environments supporting convective clouds are broadly known, there is currently no unifying theory on how joint variations in different environmental properties impact convective cloud properties. The overaching goal of this research is to assess the response of convective clouds to changes in the dynamic, thermodynamic and aerosol properties of the local environment. To achieve our goal, two tools for examining convective cloud properties and their environments are first described, developed and enhanced. This is followed by an examination of the response of convective clouds to changes in the dynamic, thermodynamic and aerosol properties using these enhanced tools. In the first study comprising this dissertation, we assess the performance of small temperature, pressure, and humidity sensors onboard drones used to sample convective environments and convective cloud outflows by comparing them to measurements made from a tethersonde platform suspended at the same height. Using 82 total drone flights, including nine at night, the following determinations about sensor accuracy are made. First, when examining temperature, the nighttime flight temperature errors are found to have a smaller range than the daytime temperature errors, indicating that much of the daytime error arises from exposure to solar radiation. The pressure errors demonstrate a strong dependence on horizontal wind speed with all of the error distributions being multimodal in high wind conditions. Finally, dewpoint temperature errors are found to be larger than temperature errors. We conclude that measurements in field campaigns are more accurate when sensors are placed away from the drone's main body and associated propeller wash and are sufficiently aspirated and shielded from incoming solar radiation. The Tracking and Object-Based Analysis of Clouds (tobac) tracking package is a commonly used tracking package in atmospheric science that allows for tracking of atmospheric phenomena on any variable and on any grid. We have enhanced the tobac tracking package to enable it to be used on more atmospheric phenomena, with a wider variety of atmospheric data and across more diverse platforms than before. New scientific improvements (three spatial dimensions and an internal spectral filtering tool) and procedural improvements (enhanced computational efficiency, internal re-gridding of data, and treatments for periodic boundary conditions) comprising this new version of tobac (v1.5) are described in the second study of this dissertation. These improvements have made tobac one of the most robust, powerful, and flexible identification and tracking tools in our field and expanded its potential use in other fields. In the third study of this dissertation, we examine the relationship between the thermodynamic and dynamic environmental properties and deep convective clouds forming in the tropical atmosphere. To elucidate this relationship, we employ a high-resolution, long-duration, large-area numerical model simulation alongside tobac to build a database of convective clouds and their environments. With this database, we examine differences in the initial environment associated with individual storm strength, organization, and morphology. We find that storm strength, defined here as maximum midlevel updraft velocity, is controlled primarily by Convective Available Potential Energy (CAPE) and Precipitable Water (PW); high CAPE (>2500 J kg-1) and high PW (approximately 63 mm) are both required for midlevel CCC updraft velocities to reach at least 10 m s-1. Of the CCCs with the most vigorous updrafts, 80.9% are in the upper tercile of precipitation rates, with the strongest precipitation rates requiring even higher PW. Furthermore, vertical wind shear is the primary differentiator between organized and isolated convective storms. Within the set of organized storms, we also find that linearly-oriented CCC systems have significantly weaker vertical wind shear than nonlinear CCCs in low- (0-1 km, 0-3 km) and mid-levels (0-5 km, 2-7 km). Overall, these results provide new insights into the joint environmental conditions determining the CCC properties in the tropical atmosphere. Finally, in the fourth study of this dissertation, we build upon the third study by examining the relationship between the aerosol environment and convective precipitation using the same simulations and tracking approaches as in the third study. As the environmental aerosol concentrations are increased, the total domain-wide precipitation decreases (-3.4%). Despite the overall decrease in precipitation, the number of tracked terminal congestus clouds increases (+8%), while the number of tracked cumulonimbus clouds is decreased (-1.26%). This increase in the number of congestus clouds is accompanied by an overall weakening in their rainfall as aerosol concentration increases, with a decrease in overall rain rates and an increase in the number of clouds that do not precipitate (+10.7%). As aerosol particles increase, overall cloud droplet size gets smaller, suppressing the initial generation of rain and leading to clouds evaporating due to entrainment before they are able to precipitate.
Open Access
Freezing drizzle production in warm frontal overunning cloud layers: an observational study
(Colorado State University. Libraries, 2010) McDonough, Frank, author; Cotton, William R., advisor; Kreidenweis, Sonia M., committee member; Mielke, Paul W., Jr., committee member
National Weather Service operational and research aircraft data were used to analyze the large and small-scale structure of warm-frontal overrunning cloud layers forming freezing drizzle. Two detailed case studies, one from a maritime region (Juneau, AK), and one from a continental region (Green Bay, WI) are presented. The synoptic scale situation for both cases showed descending motion aloft, drying at the mid-levels and warming cloud top temperatures. The warming cloud top temperatures shut down the production of the ice phase and allowed supercooled liquid water to dominate the cloud microstructure. The cloud layers were formed by both isentropic lift and convective instability, although the convective layers had higher liquid water contents. In addition to helping form the clouds the warm air advection created thin warm layers aloft which allowed discrete cloud layers to form. Each of the layers had distinct thermodynamic and microphysical properties. Freezing drizzle (FZDZ) was observed in all the cloud layers but the initial formation of FZDZ was in layers detached from the boundary layer with low droplet concentrations. Radiational cooling at the highest cloud top was likely present in both cases and may have formed FZDZ, but its presence was not a necessary condition. Isobaric mixing at cloud top was observed in the maritime case and was likely present at cloud top in both cases.
Open Access
From forests to the remote ocean to smoke plumes: aerosol microphysics in diverse environments
(Colorado State University. Libraries, 2020) Hodshire, Anna Lily, author; Pierce, Jeffrey R., advisor; Jathar, Shantanu H., advisor; Collett, Jeffrey L., committee member; Farmer, Delphine K., committee member; Kreidenweis, Sonia M., committee member
To view the abstract, please see the full text of the document.
Open Access
Impacts of unconventional oil and gas development on atmospheric aerosol particles
(Colorado State University. Libraries, 2017) Evanoski-Cole, Ashley R., author; Collett, Jeffrey L., advisor; Kreidenweis, Sonia M., committee member; Pierce, Jeffrey R., committee member; Ham, Jay, committee member
Rising demands for global energy production and shifts in the economics of fossil fuel production have recently driven rapid increases in unconventional oil and gas drilling operations in the United States. Limited field measurements of atmospheric aerosol particles have been conducted to understand the impacts of unconventional oil and gas extraction on air quality. These impacts can include emissions of greenhouse gases, the release of volatile organic compounds that can be hazardous and precursors to tropospheric ozone formation, and increases in atmospheric aerosol particles. Aerosol particles can also contribute to climate change, degrade visibility and negatively impact human health and the environment. Aerosol formation can result from a variety of activities associated with oil and gas drilling operations, including emission of particles and/or particle precursors such as nitrogen oxides from on-site power generation, evaporation or leaking of fracking fluids or the produced fuel, flaring, the generation of road dust, and increases in traffic and other anthropogenic emissions associated with growing populations near drilling locations. The work presented here details how activities associated with unconventional oil and gas extraction impact aerosol particle characteristics, sources, and formation in remote regions. An air quality field study was conducted in the Bakken formation region during a period of rapid growth in oil production by unconventional techniques over two winters in 2013 and 2014. The location and time of year were chosen because long term IMPROVE network monitoring records show an increasing trend in particulate nitrate concentrations and haze in the Bakken region during the winter, strongly contrasting with sharp decreases observed across most of the U.S. The comprehensive suite of instrumentation deployed for the Bakken Air Quality Study (BAQS) included measurements of aerosol concentrations, composition, and scattering, gaseous precursors important for aerosol formation, volatile organic compounds, and meteorology. Regional measurements of inorganic aerosol composition were collected, with average concentrations of total inorganic PM2.5 between 4.78 – 6.77 µg m-3 and 1.99 – 2.52 µg m-3 for all sampling sites during the 2013 and 2014 study periods, respectively. The maximum inorganic PM2.5 concentration observed was 21.3 µg m-3 for a 48 hour filter sample collected at Fort Union National Historical Site, a site located within a dense area of oil wells. Organic aerosol measurements obtained during the second study at the north unit of Theodore Roosevelt National Park (THRO-N) featured an average concentration of 1.1 ± 0.7 µg m-3. While oil production increased from 2013 to 2014, the lower PM2.5 in 2014 can be explained by the meteorological differences. During the first study, increased snow cover, atmospheric stability, solar illumination, and differences in the dominant wind direction contributed to higher PM2.5. The enhanced concentrations of inorganic PM2.5 measured in the Bakken region were tied to regional oil and gas development. Elevated concentrations of PM2.5 were observed during periods of air mass stagnation and recirculation and were associated with VOC emissions aged less than a day, both indicating a predominant influence from local emissions. High PM2.5 concentrations occurred when low i-/n-pentane VOC ratios were observed, indicating strong contributions from oil and gas operations. The hourly measurements of gas and aerosol species in an extremely cold environment also provided a unique data set to investigate how well thermodynamic aerosol models represent the partitioning of ammonium nitrate. In general, during the coldest temperatures, the models overpredicted the formation of particulate nitrate. The formation of additional PM2.5 in this region is more sensitive to availability of N(-III) species during the coldest periods but increasingly sensitive to available N(V) when temperatures are relatively warmer and ammonia availability increases. These measurements and modeling results show that continued growth of oil and gas drilling operations in remote areas such as the Bakken region could lead to increased PM2.5 and impact haze formation in nearby federally protected lands.
Open Access
Interactions of arctic clouds, radiation, and sea ice in present-day and future climates
(Colorado State University. Libraries, 2016) Burt, Melissa Ann, author; Randall, David A., advisor; Kreidenweis, Sonia M., committee member; Kummerow, Christian D., committee member; Betsill, Michele M., committee member
The Arctic climate system involves complex interactions among the atmosphere, land surface, and the sea-ice-covered Arctic Ocean. Observed changes in the Arctic have emerged and projected climate trends are of significant concern. Surface warming over the last few decades is nearly double that of the entire Earth. Reduced sea-ice extent and volume, changes to ecosystems, and melting permafrost are some examples of noticeable changes in the region. This work is aimed at improving our understanding of how Arctic clouds interact with, and influence, the surface budget, how clouds influence the distribution of sea ice, and the role of downwelling longwave radiation (DLR) in climate change. In the first half of this study, we explore the roles of sea-ice thickness and downwelling longwave radiation in Arctic amplification. As the Arctic sea ice thins and ultimately disappears in a warming climate, its insulating power decreases. This causes the surface air temperature to approach the temperature of the relatively warm ocean water below the ice. The resulting increases in air temperature, water vapor and cloudiness lead to an increase in the surface downwelling longwave radiation, which enables a further thinning of the ice. This positive ice-insulation feedback operates mainly in the autumn and winter. A climate-change simulation with the Community Earth System Model shows that, averaged over the year, the increase in Arctic DLR is three times stronger than the increase in Arctic absorbed solar radiation at the surface. The warming of the surface air over the Arctic Ocean during fall and winter creates a strong thermal contrast with the colder surrounding continents. Sea-level pressure falls over the Arctic Ocean and the high-latitude circulation reorganizes into a shallow "winter monsoon." The resulting increase in surface wind speed promotes stronger surface evaporation and higher humidity over portions of the Arctic Ocean, thus reinforcing the ice-insulation feedback. In the second half of this study, we explore the effects of super-parameterization on the Arctic climate by evaluating a number of key atmospheric characteristics that strongly influence the regional and global climate. One aspect in particular that we examine is the occurrence of Arctic weather states. Observations show that during winter the Arctic exhibits two preferred and persistent states — a radiatively clear and an opaquely cloudy state. These distinct regimes are influenced by the phase of the clouds and affect the surface radiative fluxes. We explore the radiative and microphysical effects of these Arctic clouds and the influence on these regimes in two present-day climate simulations. We compare simulations performed with the Community Earth System Model, and its super-parameterized counterpart (SP-CESM). We find that the SP-CESM is able to better reproduce both of the preferred winter states, compared to CESM, and has an overall more realistic representation of the Arctic climate.
Open Access
Investigation of a new microchip electrophoresis instrument for semi-continuous aerosol composition measurements
(Colorado State University. Libraries, 2012) Evanoski-Cole, Ashley R., author; Collett, Jeffrey L., advisor; Henry, Charles S., committee member; Kreidenweis, Sonia M., committee member
The high variability of atmospheric aerosol composition over both time and space and their importance to the global radiation budget, biogeochemical processes, human health, atmospheric visibility and other important issues has motivated the development of a novel instrument to measure temporal and geographical trends of aerosol composition. The aerosol microchip electrophoresis (ACE) instrument uses a water condensation growth tube to collect water soluble aerosols. Rapid separation and detection of common inorganic ions (chloride, nitrate and sulfate) and one organic acid (oxalate) in the collected aqueous sample is achieved using microchip capillary electrophoresis coupled with conductivity detection. The ACE system was tested in multiple pilot field studies and compared with measurements collected by a particle-into-liquid sampler coupled with an ion chromatograph (PILS-IC) and filter samples. Laboratory tests were also performed with generated aerosol to test the accuracy of ACE. The ACE system has the advantage of being able to achieve fast semi-continuous measurements with time resolution up to one minute. Additionally, the small size footprint and low manufacturing cost make ACE an ideal field instrument to attain rapid and sensitive aerosol composition measurements.
Open Access
Morphology, lifecycles, and environmental sensitivities of tropical trimodal convection
(Colorado State University. Libraries, 2022) Sokolowsky, George Alexander, author; van den Heever, Susan C., advisor; Maloney, Eric D., committee member; Kreidenweis, Sonia M., committee member; Jathar, Shantanu, committee member
Convective clouds are ubiquitous in the tropics and typically follow a trimodal distribution of cumulus, congestus, and cumulonimbus clouds. Due to the crucial role each convective mode plays in tropical and global transport of heat and moisture, there has been both historical and recent interest in the characteristics, sensitivities, and lifecycles of these clouds. However, designing novel studies to further our knowledge has been challenging due to several limitations: the extensive computing resources needed to conduct modeling studies at sufficient resolution and scale to capture the trimodal distribution in detail; the lack of analysis tools which can objectively detect and track these clouds throughout their lifetime; and a need for more observational and modeling data of the tropical convective environments that produce these clouds. In this dissertation, three distinct but related studies that address these problems to advance the knowledge of our field on the morphology, lifecycles, and environmental sensitivities of tropical trimodal convection are presented. The first study examines the sensitivities of the tropical trimodal distribution and the convective environment to initial aerosol loading and low-level static stability. The Regional Atmospheric Modeling System (RAMS) configured as a Large Eddy Simulation (LES) is utilized to resolve all three modes in detail through two full diurnal cycles. Three initial static stabilities and three aerosol profiles are independently and simultaneously varied for a suite of nine simulations. This research found that (1) large aerosol loading and strong low-level static stability suppress the bulk environment and the intensity and coverage of convective clouds; (2) cloud and environmental responses to aerosol loading tend to be stronger than those from static stability; (3) the effects of aerosol and stability perturbations modulate each other substantially; (4) the deepest convection and highest dynamical intensity occur at moderate aerosol loading, rather than at low or high loading; and (5) most of the strongest feedbacks due to aerosol and stability perturbations are seen in the boundary layer (the latter being applied within the boundary layer themselves), though some are stronger above the freezing level. The second study presented seeks to further enhance an artificial intelligence analysis tool, the Tracking and Object-Based Analysis of Clouds (tobac) Python package, from both a scientific and procedural standpoint to enable a wider variety of research uses, including process-level studies of tropical trimodal convection. Scientific improvements to tobac v1.5 include an expansion of the tool from 2D to 3D analyses and the addition of a new spectral filtering tool. Procedural enhancements added include greater computational efficiency, data regridding capabilities, and treatments for processing data with singly or doubly periodic boundary conditions (PBCs). My distinct contributions to this work focused on the 2D to 3D expansion and the PBC treatment. These new capabilities are presented through figures, schematics, and discussion of the new science that tobac v1.5 facilitates, such as the analysis of large basin-scale datasets and detailed simulations of layered clouds, that would have been impossible before. Finally, the last study in this dissertation is a process-focused modeling study on the sensitivities of upscale growth of tropical trimodal convection to environmental aerosol loading. This project was enabled by the scientific and procedural improvements to tobac discussed in the second study, in particular the new abilities of tobac to detect and track objects in 3D and with model PBCs. Here, we used a subset of RAMS simulations from the first study, where only aerosol loading was changed and the upscale growth from shallow cumulus through congestus and cumulonimbus during the nighttime hours was investigated. This study revealed that moderately increasing aerosol loading enhances collision-coalescence processes in the middle of the cloud, which delays initial glaciation but promotes it later in the growth period. Greatly increasing aerosol, however, produces a cloud structure with a more extreme aspect ratio and greater entrainment aloft that rapidly loses buoyancy and vertical velocity with height, as well as exhibiting a greater amount of condensate loading towards the top of the cloud. We also found the relative timing of these processes to be especially important, with more rapid initial growth and lofting of condensate often inhibiting deeper convective growth.
Open Access
Observations of atmospheric reactive nitrogen species and nitrogen deposition in the Rocky Mountains
(Colorado State University. Libraries, 2012) Benedict, Katherine B., author; Collett, Jeffrey L., advisor; Kreidenweis, Sonia M., committee member; van den Heever, Susan C., committee member; Hamm, Jay, committee member
To view the abstract, please see the full text of the document.