Browsing by Author "Collett, Jeffrey L., advisor"

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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 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
Atmospheric reactive nitrogen in Rocky Mountain National Park
(Colorado State University. Libraries, 2018) Shao, Yixing, author; Collett, Jeffrey L., advisor; Schumacher, Russ, committee member; Jathar, Shantanu, committee member; Benedict, Katherine, committee member
The Front Range urban corridor in Colorado, located east of Rocky Mountain National Park (RMNP), includes a variety of urban sources of nitrogen oxides, while high emissions of ammonia are found in agricultural sources on the eastern plains of Colorado. The spatial distribution and temporal variation of ammonia and other reactive nitrogen species in the region is not well characterized. Periods of upslope flow can transport atmospheric reactive nitrogen from the Front Range and eastern Colorado, contributing to nitrogen deposition in the park. Deposition of excess atmospheric reactive nitrogen in Rocky Mountain National Park poses threats to sensitive ecosystems. It is important to characterize temporal variation and spatial distribution of reactive nitrogen in the region to better understand the degree to which emission sources in the northeastern plains of Colorado impact RMNP and how meteorological conditions are associated with transport of ammonia to the park. Mobile and in-situ measurements of reactive nitrogen gases and particles were made between 2015 and 2016 in northeastern Colorado and RMNP. Gaseous ammonia was measured with high-time resolution instruments (a Picarro cavity-ring down spectrometer and an Air Sentry ion mobility analyzer); 24-hr integrated concentrations of trace gases and PM2.5 chemical composition in RMNP were measured by URG denuder/filter systems coupled with lab analysis; wet nitrogen deposition was collected with an automated precipitation collector followed by lab analysis. Model outputs from The Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) was also included for examining transport of ammonia source plumes. Diurnal and seasonal variability of ammonia concentrations and some other reactive nitrogen species were characterized with high time-resolution measurement data. Repeating diurnal cycles were found in Greeley and RMNP. Ammonia concentrations usually increase in the morning and reach maxima around noon in RMNP, while at Greeley ammonia builds up during the night followed by a rapid decrease after sunrise. A seasonal pattern of ammonia levels was also revealed, with higher concentrations observed during summer. When combined with wind data it is clear that elevated ammonia levels in RMNP were associated with easterly transport from the eastern plains of Colorado. The median daily averaged ammonia concentrations measured in Greeley, Loveland and RMNP are 26.2 ppb, 6.3 ppb and 1.1 ppb respectively. Considerable ammonia variability was found in NE Colorado with higher concentrations measured close to CAFOs and source regions. This was particularly clear in mobile NH3 observations where distinct plumes of ammonia were observed away from confined animal feeding operation (CAFOs) sources. Spatial variations, particularly in the north-south direction, were observed to be strongly dependent on meteorology as highlighted by HYSPLIT back trajectories. This study also evaluates the pilot Early Warning System which informs agricultural producers of impending upslope events that are likely to transport nitrogen from eastern Colorado to the park, so that management practices may be implemented to reduce nitrogen emissions. The performance of the meteorological forecasting was evaluated using continuous measurements of atmospheric ammonia concentrations in the RMNP, as well as the wet nitrogen deposition data from 2015. It was found that the model showed skill in capturing some large wet nitrogen deposition events in the park.
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
Composition of fine particles in Carlsbad Caverns National Park and implications for sources and visibility impacts
(Colorado State University. Libraries, 2022) Naimie, Lillian E., author; Collett, Jeffrey L., advisor; Benedict, Katherine B., committee member; Fischer, Emily V., committee member; Jathar, Shantanu, committee member
The Carlsbad Caverns Air Quality Study (CarCavAQS) was designed to examine the influence of regional sources, including urban emissions, increased oil and gas development, wildfires and other biogenic sources, and soil dust on the park, including impacts on fine particle haze, ozone, and nitrogen deposition. Field measurements of aerosols, trace gases, and deposition were conducted from 25 July through 5 September 2019. Here the focus is on observations of the composition and concentration of fine particles and key trace gas precursors to understand important contributing species, their sources, and associated impacts on haze. Measurements focused on fine particulate matter (PM2.5) including mass, major ions, water soluble organic carbon (WSOC), and black carbon (BC) from various high time-resolution instruments as well as an Interagency Monitoring of Protected Visual Environments (IMPROVE) sampler. Supplemental measurements included denuder-filter pack sampling for inorganic gases (HNO3 and NH3) and a Picarro cavity ring down spectrometer for methane (CH4). High-time resolution (6-minute) PM2.5 mass ranged up to 31.8 μg m−3, with an average of 7.67 μg m−3. The main inorganic ion contributions were sulfate (avg 1.3 μg m−3), ammonium (avg 0.30 μg m−3), calcium (Ca2+) (avg 0.22 μg m−3), nitrate (avg 0.16 μg m−3), and sodium (avg 0.057 μg m−3). The WSOC average concentration was 1.2 μg C m−3. Inorganic ion concentrations had significant, sharp spikes in Ca2+, consistent with local dust generation and transport. Ion balance analysis suggests one period of acidic aerosol, the importance of ammonium and calcium in neutralizing sulfate, and significant reactions of nitric acid with sea salt and soil dust. The sums of PILS ion and WSOC concentrations, the latter multiplied by a factor of 1.8 to account for elements other than carbon, were not enough to reach mass closure with the TEOM PM2.5 mass concentrations, suggesting that insoluble species are also an important component of the aerosol at CAVE. IMPROVE sampler data, including insoluble species had good agreement between total PM2.5 mass and speciated PM2.5 aerosol mass. Sulfate is the major contributor to modeled light extinction in the 24-hour IMPROVE data set. Higher time resolution data had periods of significant light extinction from black carbon as well as sulfate, with a maximum 1-hour extinction value of 90 Mm−1. Analysis of transport patterns indicated clear enrichment of sulfate, BC, and CH4 during periods when transport came from the southeast, the direction of greatest abundance of oil and natural gas development. Air masses transported from the northeast, a region of high agricultural activity, were enriched in ammonia.
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
Estimating emission rates of volatile organic compounds from oil and natural gas operations in the Piceance Basin
(Colorado State University. Libraries, 2015) MacDonald, Landan Patrick, author; Pierce, Jeffrey R., advisor; Collett, Jeffrey L., advisor; Ham, Jay M., committee member
Oil and natural gas production has been steadily increasing in Colorado for the past 10 years. Garfield County is partially located above the natural gas rich Piceance Basin. Horizontal drilling techniques provide increased access to subsurface gas deposits while hydraulic fracturing is employed to increase the permeability of the tight gas formations by pumping pressurized fluids into the ground to allow more cost-effective oil and gas extraction. Once fractured, the fluid is allowed to flow back to the surface to be captured before the well is considered producing. Our team conducted field measurements from 2013 to 2015 in Garfield County to determine emission rates of methane, hazardous air pollutants, and ozone precursors at 18 oil and gas operations. Drilling and well completion operations were targeted because they are understudied relative to production. We estimate the emission rates of methane and 58 additional VOCs (focusing on benzene, toluene, and ethane) for three common operations. We found benzene had mean emission rates of 0.72, 0.23, and 0.055 g/s for drilling, hydraulic fracturing, and flowback operations respectively. We calculated mean methane emission rates of 6.2, 29, and 64 g/s for drilling, hydraulic fracturing, and flowback operations respectively. We use the estimated methane emission rates from drilling and well completion operations to compare to typical well lifetime emissions during a 30 year production phase and find that drilling and well completion operations may be contributing from 0.1 to 10% of total well pad emissions. These results are based on a limited sampling size (18 sites) and limited overall measurement time (4.25 hours of total measurement time included in results). It is possible we did not perform measurements for long enough periods of time at enough sites. This study is beginning to fill the information gap by focusing on drilling and well completion operations. AERMOD is an atmospheric dispersion model used for new source apportionment. We compared our measured concentration fields to AERMOD predicted concentration fields by replicating fieldwork locations and conditions. Meteorological conditions were taken from an on-site meteorological station for use in the dispersion model. Comparing to the measurements, we found there was a low log-mean bias (-0.007) with a large amount of scatter (r = 0.0007). Additionally, we use AERMOD and data from the NCEP North American Regional Reanalysis database to predict the distribution of concentrations experienced throughout for various meteorological conditions in Garfield County at various distances surrounding oil and gas wells. We normalized these predicted concentration fields by emission rate and created cumulative distribution functions.
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
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
Micrometeorological studies of a beef feedlot, dairy, and grassland: measurements of ammonia, methane, and energy balance closure
(Colorado State University. Libraries, 2018) Shonkwiler, Kira Brianne, author; Collett, Jeffrey L., advisor; Ham, Jay M., committee member; Kreidenweis, Sonia, committee member; Schumacher, Russ, committee member; Archibeque, Shawn, committee member
Ammonia emissions from concentrated animal feeding operations (CAFOs; most of which are beef feedlots) near the Colorado Front Range are suspected to be a large regional input of reactive nitrogen which has been found to accumulate and cause deleterious effects in nearby downwind Class I areas like Rocky Mountain National Park. Methane (CH4) is a strong greenhouse gas (GHG) emitted in large amounts from dairy anaerobic lagoons used for liquid manure management. Lagoon systems account for over half of the manure management-based CH4 emissions from agriculture in the US. There is a strong need for more emissions measurements from CAFOs like feedlots and dairies. For these data to be trusted, well-developed techniques must be utilized at emissions measurement sites and such techniques should be validated in ideal scenarios. Three micrometeorological studies were performed involving measurement of emissions using micrometeorological methods in the surface layer. The first study involved estimating summertime NH3 emissions from a 25,000-head beef feedlot in Northern Colorado. Two different NH3 sensors were used: a cavity ring down spectroscopy analyzer collected data at a single point while a long-path FTIR collected data along a 226-m long transect, both deployed along the same fenceline. Concentration data from these systems were used with two inverse dispersion models (FIDES, an inverse solution to the advection dispersion equation; and WindTrax, a backward Lagrangian stochastic model). Point sensor concentrations of NH3 were similar to line-integrated sensor concentrations suggesting some spatial uniformity in emissions. Emissions had a diurnal pattern (i.e., afternoon peak with minimum in early morning) that was driven by temperature. Emissions predicted by WindTrax were 25.2% higher than those from FIDES. Point vs. long-path measurements of NH3 had minimal effect on predicted emissions. The mean NH3 emission factor (EF) was 80 ± 39 g NH3 hd−1 d−1, with 40.0% of dietary-N emitted as NH3. The second study involved using eddy covariance and WindTrax to quantify CH4 emissions from a 3.9-ha anaerobic lagoon serving a 1400-head dairy in northern Colorado. Methane emissions followed a strong seasonal pattern correlated with temperature of the organic sludge layer on the bottom of the lagoon. Fluxes started increasing in late spring (May; ~10°C), increased rapidly in Jun (10-15°C) peaked in the summer (Jul/Aug; ~18-20°C) and remained high until mid-autumn (late Oct/early Nov; ~10°C). Fluxes then decreased and remained consistently low (up to 10 times less than peak emissions) until microbial activity ramped up again in May. The EC signal was very dependent on wind direction, with highest concentrations and fluxes associated with the direction of the lagoon. Gap-filled data showed a slight diurnal pattern to all seasons, with tenfold increases in diurnal values for summer over winter. Additionally, EFs for the lagoon varied by season with lows in the winter and highs in the summer with an annual mean of 819 ± 774 g CH4 hd-1 d-1. WindTrax overestimated EC for the lagoon (1163 ± 1049 g CH4 hd-1 d-1 versus 819 ± 774 g CH4 hd-1 d-1), but this difference may be attributable to differences in the sampling footprint and stability conditions. IPCC Tier 2-calculated EFs were extremely close to EC-based measurements and WT-based estimates. The third study involved using eddy covariance in an ideal environment (tallgrass prairie in Kansas) to test the reasons behind the "energy balance (EB) closure problem" at two landscape positions. This problem can cast uncertainty on flux measurements made by EC. One upland and one lowland EC tower each were used to measure EB components (i.e., net radiation, Rn; soil heat flux, G; total change in heat storage, deltaS; and sensible and latent heat fluxes, H and λE) during the summers of 2007 and 2008. To maximize closure, special attention was given to reduce all forms of instrumentation error and account for heat storage and photosynthesis between the soil and the reference height. Landscape position had little effect on G, H, and Rn; differences were ≤ 2% between sites. Lowland λE was 8% higher than upland λE because of greater biomass and soil moisture. On average, EB closure (i.e., Σ[λE+H] / Σ[Rn–G–ΔS]) was 0.88 and 0.94 at the upland and lowland sites, respectively. Closure was not correlated with friction velocity or the stability of the surface boundary layer. Given high confidence in Rn, G, and ΔS, turbulent fluxes depend directly on vertical velocity (w), and the fact that a systematic underestimation of w was recently found in literature, lack of closure may have resulted largely from anemometer-based underestimates of w.
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
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Open Access
The validation of emission rate estimation methods
(Colorado State University. Libraries, 2015) Wells, Bradley, author; Collett, Jeffrey L., advisor; Pierce, Jeffrey, advisor; Ham, Jay, committee member
Oil and natural gas production throughout the United States has been dramatically increasing in recent years, due in large part to hydraulic fracturing processes and horizontal drilling techniques that allow for extraction from unconventional wells. The rise in well drilling and completion activities raises concern over potential air quality impacts on nearby communities. Methane, other volatile organic compounds (VOCs), and nitrogen oxides (NOₓ) may be emitted into the atmosphere during well development and production activities. Methane is a greenhouse gas, VOCs and NOₓ act as ozone precursors, and some VOCs are classified as air toxics. For these reasons, there is a need to accurately quantify the rate of emissions of these gases into the atmosphere from oil and gas development and production. One such emission rate estimation technique is the tracer ratio method (TRM). The TRM requires access to a well site and involves the release of a passive tracer gas as close to the source of emissions as possible. This known emission rate is multiplied by the ratio of the downwind concentrations of emission gas to the tracer gas (both in excess of background) to derive an estimate of the emission gas emission rate. Another technique, recently developed by the Environment Protection Agency, utilizes a simplified point source Gaussian plume (PSG) dispersion model. This approach requires only one mobile downwind measurement location for both concentration and meteorological measurements, without the need for site access; it does not require a tracer gas. In order to evaluate the effectiveness of these techniques, a series of experiments were conducted at Christman airfield in Fort Collins, Colorado. These experiments involved releasing both acetylene, as a tracer gas, and methane (to simulate an emission source) at controlled flow rates to compare the predicted emission rate of methane to its actual emission rate. A vehicle equipped with a PICARRO methane and acetylene analyzer traversed or remained stationary within the gas plume to provide real-time concentration measurements of both gases. A 3-D sonic anemometer was used to characterize local meteorological conditions. The TRM is evaluated using both a mobile transect and a stationary approach. There is an overall positive bias in both cases. Our best results are obtained when sources are co-located during a stationary analysis and changes in background methane concentrations are determined and corrected. In these cases the mean bias is +9% with σ=22% (standard deviation about the mean bias). The separation of tracer and emission gas sources in the mobile transect analysis is the largest cause for uncertainty. The mean bias when sources are separated is +83% (σ=99%), as opposed to transect analyses of co-located sources which have a mean bias of +33% (σ=31%). The PSG technique, which involves a 20 minute stationary analysis, contains more inconsistent results compared to the stationary approach performed by the TRM (mean bias of methane emission rate prediction +34%, σ=123%). Most interesting of note is that for nearly every sample the bias in the prediction of the emission rate of acetylene is more negative than the bias in methane emission rate predictions (mean bias of acetylene emission rate prediction -19%, σ=128%). This suggests possible biases in the acetylene release rate or concentration measurement; however, at this time the issue cannot be located. Regardless, a stationary TRM technique produces the best results, and its use is recommended when site access is available for tracer release.
Open Access
Volatile organic compound and methane emissions from well development operations in the Piceance Basin
(Colorado State University. Libraries, 2016) Hilliard, Noel G., author; Collett, Jeffrey L., advisor; Fischer, Emily V., committee member; Ham, Jay M., committee member; Hecobian, Arsineh, committee member
The natural gas industry in Colorado has experienced significant growth in the last decade due to widespread use of unconventional natural gas extraction technologies. Garfield County is located in the Rocky Mountain Region on the western slope of Colorado above the Piceance Basin. Natural gas wells in this region penetrate the William’s Fork formation, located approximately 4,000 ft. below the surface, which is a tight sand formation known to be rich in natural gas. Horizontal drilling increases the extraction potential of natural gas stored in several sandstone lenses. Hydraulic fracturing is a stimulation technique used to maximize the flow and efficiency of natural gas transport to the surface from unconventional reservoirs. Once the formation is adequately cracked, 10-50% of the hydraulic fluid flows back to the surface . Our field team collected samples in Garfield County between 2013-2015 to measure methane, ozone precursors, and air toxics associated with natural gas extraction activities. Very few studies have provided direct observations of VOC emissions from individual well development activities. Emission rates of 48 VOCs and methane were determined using the tracer ratio method for three well development operations: drilling, hydraulic fracturing (fracking), and flowback for a subset of samples collected. Methane had mean emission rates of 1.57, 6.78, and 25.6 g s-1 for drilling, hydraulic fracturing, and flowback operations respectively, while toluene had mean emission rates of 1.24, 0.469, and 0.437 g s-1 for these operations. Measured emission rates were used to determine if specific VOCs were well correlated with each other and/or methane emission rates. Strong correlations between individual VOC emission rates and methane were investigated to assess whether methane emission rates might serve as useful surrogates for emission rates of individual VOCs, which are less easily measured. We found that methane and ethane appear to be emitted from the same sources for all operation types indicating that methane emission rates may be useful surrogates for ethane emission rates. Methane emission rates appear not to be very useful surrogates for heavier VOCs, including C5-C10 alkanes, alkenes, and aromatics. Concentration ratios of source-specific tracer compounds were investigated to determine the source signatures of individual operation types. We found that drilling emissions appear to be primarily influenced by combustion, while flowback emissions are primarily influenced by the release of natural gas and other substances from the well.
Open Access
Volatile organic compound concentrations and the impacts of future oil and natural gas development in the Colorado Northern Front Range
(Colorado State University. Libraries, 2018) Weber, Derek T., author; Collett, Jeffrey L., advisor; Fischer, Emily V., committee member; Jathar, Shantanu H., committee member; Hecobian, Arsineh, committee member
Recent advances in unconventional extraction of oil and natural gas (O&NG) have caused an increase in the number of wells in the Colorado Northern Front Range (CNFR) which has doubled Colorado's natural gas production over the last 15 years. Increased O&NG activity can lead to increased emissions of Volatile Organic Compounds (VOCs) which may negatively impact air quality and human health. This study looks at five sites (an elementary school, residential area, Fossil Creek Natural Area, Soapstone Natural Area, and a gas station) in Fort Collins and Timnath with the objectives of determining the gradient of VOC concentrations across a subsection of the CNFR, providing a baseline to compare potentially elevated VOC concentrations from future O&NG development, and a better understanding of the influence of O&NG emissions on air quality in the CNFR. Whole air samples were collected at all locations using an evacuated 6L stainless steel canister equipped with a calibrated flow controller that sampled at a constant flow rate for approximately 1 week. Sampling began at the elementary school and gas station in the summer of 2015 and concluded in November of 2016. Sampling at the two natural areas and the residential area took place in the fall of 2015. VOC concentrations were analyzed using an online gas chromatography flame ionization detector (GC-FID) system. An in-situ real-time GC was also deployed along with an All-In-One (AIO) weather station at the residential area providing hourly VOC and meteorological measurements for approximately 3 weeks in the fall of 2015. A suite of 48 VOCs were measured in this study. Ambient concentrations of BTEX compounds (Benzene, Toluene, Ethylbenzene, and Xylenes) are often of particular interest due to their carcinogenic effects and toxicity; therefore, they were studied in-depth as part of this thesis. Benzene was found to have median ambient concentration at the elementary school, residential area, Fossil Creek Natural Area, Soapstone Natural Area, and the gas station of 0.18, 0.14, 0.32, 0.09, and 0.55ppbv, respectively. Through the use of VOC correlations with propane and acetylene and VOC ratios, it was determined that O&NG emissions have a large influence on ambient VOC concentrations in the CNFR. The mean ratio of i-pentane to n-pentane found at the elementary school, residential area, Fossil Creek Natural Area, Soapstone Natural Area, and the gas station was 1.07, 1.17, 1.16, 1.05, and 2.35, respectively. This indicates that the elementary school and Soapstone Natural Area are strongly influence by O&NG emissions while the residential area and Fossil Creek Natural Area have a mixed influence from O&NG activity as well as vehicular emissions. In contrast the gas station, displayed a clear combustion signature, as expected. Additional VOC ratios were utilized; however, i-pentane to n-pentane ratio was determined to be the most robust tool to assess source apportionment in the CNFR. In addition, through the use of meteorological data coupled with the real-time GC VOC measurements, there is strong evidence that local O&NG sources can have a large impact on air quality at the residential area. The OH reactivity at each location was evaluated in order to compare the ozone production potential by the VOCs measured at each site. Fossil Creek NA showed the largest total OH reactivity in the fall while Soapstone NA displayed the lowest. At Soapstone NA, 66.7% of the total OH reactivity resulted from aromatics, which is the highest, and 11.4% resulted from alkenes, which is the lowest compared to each group's contribution at other sites. At the elementary school, 3.2% of the OH reactivity in the summer was attributed to isoprene, whereas in the fall, winter, and spring only 2.0%, 0.41%, and 0.76% of the OH reactivity resulted from isoprene, respectively. Development of new unconventional O&NG wells is ongoing in the CNFR and there are plans to develop wells in close proximity to the elementary school. The American Meteorological Society (AMS)/Environmental Protection Agency (EPA) steady-state dispersion model AERMOD was utilized to project the potential increased concentration of benzene as a result of this development. The model was run utilizing the 5th, 25th, median, 75th, and 95th percentile emission rates of benzene found by a past study at production sites in the CNFR. The annual average concentration increases above background at the school (0.18 ± 0.08ppbv) for the 5th, 25th, median, 75th, and 95th percentile emission rates were found to be 0.0067, 0.11, 0.33, 0.89, and 6.7ppbv, respectively. The strongest benzene enhancement at the school occurred 0:00 (midnight) - 08:00 and 17:00 - 23:00 (0.46ppbv); however, during school attendance hours (08:35 - 15:13) the concentration increase was 0.024ppbv.
Open Access
Wintertime aerosol in Las Vegas, Nevada
(Colorado State University. Libraries, 2014) Brown, Steven G., author; Collett, Jeffrey L., advisor; Kreidenweis, Sonia, committee member; Roberts, Paul, committee member; Heald, Colette, committee member; Marchese, Anthony, committee member
Numerous studies have found adverse health effects in subjects who live next to major roadways due to air pollution; in particular, there can be severe impacts on lung function and development in children living and/or attending school next to major roadways due to their exposure to air pollutants, including particulate matter (PM) or aerosol. The composition of aerosol at an elementary school next to a major freeway in Las Vegas, Nevada during winter 2008 was measured using a suite of measurements. An Aerodyne High Resolution Aerosol Mass Spectrometer (HR-AMS) was used to quantify the composition of non-refractory PM1 aerosol, including organic matter (OM); an Aethalometer was used to quantify black carbon (BC); a Sunset OCEC analyzer was used to measure organic and elemental carbon (OC, EC); and a particle-into-liquid system (PILS) coupled to two ion chromatographs (IC) was used to measure fine particle ions. Hi-volume PM2.5 samplers were used to collect aerosol on quartz fiber filters at between 2 and 24 hour intervals during the study, a subset of which were analyzed for PAHs and the biomass burning tracer levoglucosan. Data were analyzed by positive matrix factorization (PMF) to determine the amount of fresh, hydrocarbon-like organic aerosol (HOA), more oxidized OA (low-volatility and semi-volatile OA [LV-OOA, SV-OOA]) and biomass burning OA (BBOA). PM1 aerosol was predominantly carbonaceous, with OM plus BC accounting for 74% of the overall average 6.9 μg/m3 of PM measured. BC had a diurnal pattern similar to traffic volume, while OM was higher in the evening compared to the morning. OM was a mixture of fresh HOA, urban- and regional-scale OOA, and BBOA; in the evening, SV-OOA and BBOA peaked, while HOA concentrations were on average the same in the morning and evening, similar to BC. OM/OC ratios were low (1.52 ±0.14 on average) during the morning rush hour (average OM = 2.4 μg/m3) when vehicular emissions dominate this near-road measurement site, and even lower (1.46 ± 0.10) in the evening (average OM=6.3 μg/m3), when a combination of vehicular and fresh residential biomass burning emissions was typically present during a period characterized by strong atmospheric stability. While nitrate and sulfate had size distributions typical of secondary species with a sharp peak in particle diameter between 400 nm and 500 nm, OM had a broader distribution between 100 nm and 400 nm diameter particles, reflecting its combination of fresh, smaller particles and aged, larger particles. OM concentrations were on average similar between periods when the sampling site was upwind and downwind of the freeway, though during the morning OM concentrations were higher under downwind conditions, as was the fraction of HOA.