Browsing by Author "Collett, Jeffrey L., committee member"
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Item Open Access Aerosol single-scattering albedo retrieval over North Africa using critical reflectance(Colorado State University. Libraries, 2010) Wells, Kelley Carlene, author; Kreidenweis, Sonia M., advisor; Stephens, Graeme L., 1952-, committee member; Remer, Lorraine Ann, committee member; Collett, Jeffrey L., committee member; Peel, Jennifer L., committee memberThe sign and magnitude of the aerosol radiative forcing over bright surfaces is highly dependent on the absorbing properties of the aerosol. Thus, the determination of aerosol forcing over desert regions requires accurate information about the aerosol single-scattering albedo (SSA). However, the brightness of desert surfaces complicates the retrieval of aerosol optical properties using passive space-based measurements. The aerosol critical reflectance is one parameter that can be used to relate top-of-atmosphere (TOA) reflectance changes over land to the aerosol absorption properties, without knowledge of the underlying surface properties or aerosol loading. Physically, the parameter represents the TOA reflectance at which increased aerosol scattering due to increased aerosol loading is balanced by increased absorption of the surface contribution to the TOA reflectance. It can be derived by comparing two satellite images with different aerosol loading, assuming that the surface reflectance and background aerosol are similar between the two days. In this work, we explore the utility of the critical reflectance method for routine monitoring of spectral aerosol absorption from space over North Africa, a region that is predominantly impacted by absorbing dust and biomass burning aerosol. We derive the critical reflectance from Moderate Resolution Spectroradiometer (MODIS) Level 1B reflectances in the vicinity of two Aerosol Robotic Network (AERONET) stations: Tamanrasset, a site in the Algerian Sahara, and Banizoumbou, a Sahelian site in Niger. We examine the sensitivity of the critical reflectance parameter to aerosol physical and optical properties, as well as solar and viewing geometry, using the Santa Barbara DISORT Radiative Transfer (SBDART) model, and apply our findings to retrieve SSA from the MODIS critical reflectance values. We compare our results to AERONET-retrieved estimates, as well as to measurements of the TOA albedo and surface fluxes from the Geostationary Earth Radiation Budget (GERB) experiment, Atmospheric Radiation Measurement (ARM) program, and Clouds and the Earth's Radiant Energy System (CERES) data. Spectral SSA values retrieved at Banizoumbou result in TOA forcing estimates that agree with CERES measurements within ± 5 W m-2 for dusty conditions; however, the retrieved SSA translates to a much larger positive TOA forcing than CERES in the presence of dust-biomass burning mixtures. At Tamanrasset, the retrieval captures changes in aerosol absorption from day to day, but the SSA appears to be biased high when compared to AERONET and CERES. This may be due to the higher surface reflectance in this region, an overestimation of the dust aerosol size, or changing background aerosol between the clean and polluted day. Our retrieval results indicate that we can be most confident in the retrieved SSA for scattering angles between 120° and 160°, satellite view angles less than ~45°, and in cases when the background aerosol on the cleaner day is non-absorbing.Item Open Access An investigation of ammonia and inorganic particulate matter in California during the CalNex campaign(Colorado State University. Libraries, 2012) Schiferl, Luke D., author; Heald, Colette L., advisor; Collett, Jeffrey L., committee member; Ham, Jay M., committee memberOver the last century, the rise of industrial agriculture has greatly increased the emission of ammonia (NH3) from livestock waste and synthetic crop fertilizers to the atmosphere. Ammonium (NH4+) aerosol, which can be formed through the neutralization of atmospheric acids by NH3, is a key component of particulate matter (PM) in the atmosphere. PM causes negative human health effects and reduces visibility, and transport and deposition of excess NH3 can cause environmental degradation. Airborne observations of gas precursors and inorganic aerosol taken during the CalNex campaign in May and June 2010 are used in this study to investigate the role of NH3 in PM formation in California and test the representation of the key processes relevant to this chemical system in the GEOS-Chem chemical transport model. Evaluation of the 0.5° x 0.667° horizontal resolution nested model with observations shows a large underestimation (5.4 ppb median bias in the lowest 1 km) of NH3 in the Central Valley. This NH3 underestimation is lower in the area surrounding Los Angeles (LA), only 1.4 ppb. Sulfur dioxide (SO2) is also underestimated in both regions, while nitric acid (HNO3) shows little bias. Near-surface simulated inorganic PM is under-predicted by 1.28 µg sm-3 in the LA region and over-predicted in the Valley by 0.27 µg sm-3. Investigation of model sensitivity to the processes of gas-particle partitioning, wet deposition, dry deposition and emissions reveal that emissions have the largest potential for correction of model deficiencies. Increases to anthropogenic livestock NH3 emissions by a factor of 5 and anthropogenic SO2 emissions in the Valley by factors from 3 - 10 eliminates the bias in the simulation of gases in both regions and PM near LA, where under-prediction of nitrate (NO3-) is reduced from 0.64 µg sm-3 to 0.12 µg sm-3 in the lowest 1 km. An increase in NH3 emissions in the LA region is critical to capturing ammonium nitrate (NH4NO3) formation down-wind of the city core. Using this modified emissions simulation, seasonal PM differences in the two regions and the export of excess NH3 out of the Valley are explored. Mean June simulated PM concentration in the lowest 1 km is 3.48 µg sm-3 near LA (38% NO3- and 39% SO42-, by mass) and 1.98 µg sm-3 in the Valley (44% NO3- and 32% SO42-, by mass). These simulated PM concentrations are 2 times greater in the Valley in December than in June, when NH4NO3 formation is favored by colder temperatures. However, LA simulated PM concentration falls by 53% in December compared to June, likely due to lower winter NH3 emissions. Both the model and IASI satellite observations indicate that large amounts of excess NH3 are transported from the Valley to southeastern California in the summertime which may negatively affect ecosystems in this area.Item Open Access Comparison of hexavalent chromium and welding fumes inside and outside of the welding helmet(Colorado State University. Libraries, 2013) Diaz-Rivera, Karen, author; Brazile, William, advisor; Reynolds, Stephen, committee member; Collett, Jeffrey L., committee memberThe primary objective of this study was to determine if welding fumes and specific metal concentrations were significantly different between samples taken inside and outside of the welding helmet to determine the most appropriate location of the personal sampling device and best estimate exposure. Personal air samples were collected simultaneously inside and outside of the welding helmet for concentration comparison of welding fumes (n = 12) and hexavalent chromium (n = 15) during stainless steel tungsten inert gas welding tasks. A total of fifteen welders were sampled in a manufacturing setting and a brewery for a total of 27 inside and outside paired samples. A statistically significance difference (p = 0.05) between inside and outside welding helmet concentrations was found for total welding fumes, iron, total chromium, and nickel using a Wilcoxon paired test, where most of the inside-helmet concentrations were lower. Hexavalent chromium and manganese concentrations were not significantly different when comparing inside and outside welding helmet concentrations. A correlation among welding fumes, iron, nickel, and total chromium concentrations was observed utilizing Spearman's rank-order correlation. The mean for hexavalent chromium concentrations difference was 11 μg/m3, when the outlier was included in the analysis and 0.07 μg/m3 without the outlier. The median concentrations difference was 0.06 μg/m3 with or without the outlier in the analysis. The 95% confidence interval for hexavalent chromium inside concentration was 0.1 μg/m3 to 0.34 μg/m3 and 0.13 μg/m3 to 0.4 μg/m3 for outside of the welding helmet concentration. One sample set for hexavalent chromium exceeded the permissible exposure limit (PEL), recommended exposure limit (REL), and threshold limit value (TLV). Based on the results, a high variation of concentrations was found between the inside and outside of the welding helmet concentrations depending on the metal fume analyzed. Manganese had the lowest metal content in the stainless steel welding rods as well as the sampled welding fumes. The greatest variation in concentration ratios was observed for manganese and hexavalent chromium when comparing inside and outside concentrations. These two factors, lower metal contribution in welding rods and variation in concentrations can be speculated to affect the statistical non significant difference found for manganese and hexavalent chromium inside and outside of the welding helmet concentrations. The welding helmet seemed to be protective for some metals, but it should not be assumed that protection will be provided by the use of it. As for sampling location for best welding fumes assessment monitoring, it is recommended that sampling is done outside. Welders often remove their welding helmets to verify the weld, and inside of the welding helmet sampling location may be compromised as it may change when the welding helmet is in the upward position.Item Open Access Coupling an urban parameterization to an atmospheric model using an operational configuration(Colorado State University. Libraries, 2010) Nobis, Timothy E., author; Pielke, Roger A., advisor; Collett, Jeffrey L., committee member; Johnson, Richard H. (Richard Harlan), committee member; Meroney, Robert N., committee memberOperational weather centers use numerical weather prediction (NWP) models to provide forecast weather guidance. Output from these models are then used to drive non-weather decision aids such as air quality forecast or dispersion models which are sensitive to near surface weather and very important in urban areas. While NWP models are usually run at resolutions fine enough to allow them to account for mesoscale flow systems (e.g. sea breeze), they are not designed to explicitly model an urban heat island (UHI) response. Other studies have shown that the UHI can interact with and alter local mesoscale flow systems in and around urban areas. This study examines the ability of an urban parameterization to improve operational NWP characterization of the sensible weather in Washington, DC on three separate days. The urban parameterization does seemly function in a subjective fashion to create many of the typical UHI features in spite of being run at a much coarser resolution than typically used with urban parameterization studies. When compared to actual near surface temperature data, while the parameterization was found to significantly underestimate the strength of the UHI (likely a product of the resolution), it does act to reduce the forecast temperature error in the District, especially when compared against an available vertical temperature profile. The parameterization did perform more ambiguously in the transition area between the suburban and rural regions where it seems the resolution was not high enough to model the often observed sharp transition between urban and rural environment. Overall, the presence of an urban parameterization seemed to improve the model's characterization of the near surface environment around Washington, DC.Item Open Access Detection and analysis of low level tritium in rainwater for a proposed environmental monitoring program(Colorado State University. Libraries, 2014) Gillis, Jessica McDonnel, author; Brandl, Alexander, advisor; Whicker, Ward, committee member; Collett, Jeffrey L., committee memberRadioactive tritium, an isotope of hydrogen, is present at low levels in the atmosphere and can be deposited by precipitation. Tritium is produced naturally by the interaction of cosmic rays with gaseous atoms in the atmosphere, but the primary contributors to atmospheric concentrations are residues from past nuclear weapons testing and releases of tritium produced at nuclear facilities. The National Atmospheric Deposition Program (NADP) is a nationwide program that manages and analyzes rain and snow samples from networks of precipitation monitoring stations. The NADP and Savannah River National Laboratory have jointly proposed a monitoring program for tritium in rainwater in order to demonstrate the use of existing sampling locations in the NADP's National Trends Network and characterize the deposition of radionuclides in the United States. This research investigates the feasibility of measuring tritium concentrations in rainwater samples given the proposed laboratory detection range of 0.6-1.2 Bq/L. Rainwater samples were analyzed using Colorado State University's liquid scintillation counter (LSC), and minimum detectable activity concentrations on the LSC were investigated based on background count rate, count duration, and detection efficiency. To achieve the analytical capabilities and throughput proposed, count times of several hours and comparison with tritium-depleted blanks were determined to be necessary. Detection efficiencies for tritium in rainwater were affected by quench in the samples, optimization of the counting window, and LSC vial type.Item Open Access Development of a microchip electrophoresis system for online monitoring of atmospheric aerosol composition(Colorado State University. Libraries, 2011) Noblitt, Scott Douglas, author; Henry, Charles S., 1972-, advisor; Collett, Jeffrey L., committee member; Elliott, C. Michael, committee member; Strauss, Steven H., committee member; Rickey, Dawn, committee memberAtmospheric aerosols are solid or liquid particles that remain suspended in the environment for an extended time because of their size. Due to their high number concentration, low mass concentration, unique size range, and high temporal and spatial variability, atmospheric aerosols represent a significant unknown in both environmental impact and human health. Despite the importance of aerosols, current instrumentation for monitoring their chemical composition is often limited by poor temporal resolution, inadequate detection limits, lack of chemical speciation, and/or high cost. To help address these shortcomings, microchip electrophoresis (MCE) has been introduced for the semi-continuous monitoring of water-soluble aerosol composition. The MCE instrument was coupled to a water condensation particle collector (growth tube), and the integrated system is termed Aerosol Chip Electrophoresis (ACE). ACE is capable of measuring particle composition with temporal resolution of 1 min and detection limits of ~100 ng m-3. This dissertation covers the development process of the prototype ACE instrument, including the novel separation chemistry, necessary modifications to traditional microfluidic devices, and the interface between the growth tube and the microchip.Item Open Access Effect of organic nitrogen fertilizer source, application method, and application rate on ammonia volatilization from drip irrigated vegetables(Colorado State University. Libraries, 2018) Erwiha, Ghazala M., author; Davis, Jessica G., advisor; Ham, Jay M., committee member; Collett, Jeffrey L., committee memberTo view the abstract, please see the full text of the document.Item Open Access Evidence for a biological control on emissions of marine ice nucleating particles: laboratory, field and modeling results(Colorado State University. Libraries, 2017) McCluskey, Christina Song, author; Kreidenweis, Sonia M., advisor; DeMott, Paul J., advisor; Collett, Jeffrey L., committee member; Pierce, Jeffrey R., committee member; Mykles, Donald L., committee memberTo view the abstract, please see the full text of the document.Item Open Access Fine particle sources and adverse events in infants using home cardiorespiratory monitors(Colorado State University. Libraries, 2011) Mourning-Star, Phoenix, author; Peel, Jennifer L., advisor; Keefe, Thomas J., committee member; Collett, Jeffrey L., committee memberBackground: Recent research has provided a wealth of knowledge of the contributions of air pollution to adverse cardiovascular and respiratory events in sensitive populations. Source apportionment methods can be used to apportion and identify ambient sources of air pollution, which can then be used to estimate health effects of air pollution sources. Infants are thought to be particularly susceptible to air pollutant sources; however, little research has been conducted. The objective of this study was to examine the associations of ambient source apportioned fine particulate matter with bradycardia (low heart rate) and apnea (cessation of respiration) events in a cohort of infants prescribed home cardiorespiratory monitors. Methods: We utilized data from 3,629 infants within the Atlanta metropolitan statistical area who used home cardiorespiratory monitors between November 19, 1998 and December 31, 2002. Home monitors were used to record respiratory effort and heart rate to detect bradycardia and apnea events. Chemical mass balance (CMB) and positive matrix factorization (PMF) source apportionment methods for fine particulate matter (PM2.5) were used to produce 14 source profiles. Repeated-measures unconditional logistic regression using generalized estimating equations (GEEs) was used to associate cardiorespiratory events with air pollution sources. A stationary 45-dependent correlation structure was used to account for the correlation of multiple event-days for a patient. The model included age of the infant, the squared age of the infant, average daily temperature, the square of average daily temperature and indicator variables for weekend and federal holiday. Our analysis used a day, day-squared and day-cubed set of variables for the full term/normal birth weight apnea analysis to adjust for time. Cubic splines with seasonal knots for time were used to adjust for long term temporal trends in the remainder of the presented final results for apnea analyses and all of the bradycardia analyses. We performed separate analyses for zero and one-day lags of pollution. We used odds ratios (ORs) and 95% confidence intervals (CI's) as our measure of effect size to describe the odds of an event occurring. ORs from the analysis were calculated for an inter-quartile range (IQR) increase in each of the single pollutant source models. Apnea and bradycardia were evaluated separately. Results: We observed a pattern of suggestive positive odds ratios, especially in the primary analysis, such as in the woodsmoke source, which were consistent across source apportionment method and lag structure. We observed positive associations in the positive matrix factorization models for the woodsmoke source in the apnea zero-day lag for the primary analysis with an odds ratio of 1.031 (95% CI: 1.001-1.061; IQR: 0.93 µg/m3 increase). We also observed positive associations in the positive matrix factorization models for the woodsmoke source in the apnea one-day lag analysis for primary and premature/normal birth weight with an odds ratio of 1.048 (95% CI: 1.017-1.080; IQR: 0.93 µg/m3 increase) and 1.041 (95% CI: 1.006-1.077; IQR: 0.93 µg/m3 increase), respectively. The results for the full term/normal birth weight strata had stronger odds ratios than for both the primary and premature/low birth weight strata. Conclusions: Although we did observe wide confidence intervals and some protective odds ratios, we also observed stronger odds ratios in the one-day lag models compared to the zero-day lag models for the apnea events across both source apportionment methods. We observed some suggestive associations between cardiorespiratory events and source apportioned fine particulate matter that contributes to the body of air pollution literature. The access to such a large cohort of infants with the apnea and bradycardia data made this study a contribution to the understanding of the associations between cardiorespiratory events and source apportioned fine particulate matter in infants at high risk for cardiorespiratory events.Item 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 memberTo view the abstract, please see the full text of the document.Item Open Access Measurements of current-use pesticides and oxidation products using chemical ionization mass spectrometry(Colorado State University. Libraries, 2018) Murschell, Trey Daniel, author; Farmer, Delphine K., advisor; Borch, Thomas, committee member; Kennan, Alan, committee member; Collett, Jeffrey L., committee memberPesticides are both naturally occurring compounds found within a variety of plant species and also synthetic chemicals that are used to protect vulnerable organisms against disease carriers, harmful pests, and intrusive or undesirable vegetation. Pesticide use has large agricultural, economic, and health benefits which include increased staple food production, protection of susceptible ecosystems and wetlands, increased productivity of the labor force via disease control, and the creation of a booming chemical industry. In the decades following the discovery of DDT's anti-insecticidal properties, organochlorine pesticides (OCPs) were generously applied across the globe. OCPs appeared to have low toxicity to mammals, chiefly humans, but had adverse effects to non-target species like fish and predatory birds. OCPs persisted in soil, air, and water, and were transported atmospherically, as far as the Arctic. The prohibition of OCPs by most nations spurred research into less harmful and persistent pesticides. These current-use pesticides (CUPs) have mostly replaced OCPs and are applied world-wide. However, recent studies revealed the transport of CUPs to remote areas, including isolated Pacific islands, high alpine mountain lakes, and, again, the Arctic. Once in the atmosphere, these pesticides undergo physical and chemical processes that affect atmospheric lifetimes and transport, and potentially change the toxicity of the parent pesticides, which can have unforeseen impacts on sensitive ecosystems and organisms. With pesticide use perpetually linked to negative health questions and concerns, atmospheric monitoring, understanding of chemical processes, and improving analytical methods is necessary. Presented in this dissertation is work towards understanding pesticides and their chemistry in the atmosphere using real time mass spectrometry. A new calibration and measurement method for four CUPs, atrazine, metolachlor, permethrin, and trifluralin is shown in Chapter 2. Iodide chemical ionization mass spectrometry (CIMS) offers a real-time, sensitive measurement technique for herbicides, as well as other low volatility species. Presented in Chapter 3, ambient pesticide spray volatilization and post-application volatilization of two chlorophenoxy acid herbicides, 2,4-D and MCPA, were measured using acetate CIMS. Concentrations of 2,4-D were highest during the application period, while MCPA concentrations increased with increasing ambient temperature. Henry's Law constants and vapor pressure were found to be predictors for spray volatilization and post-application volatilization, respectively. OH radical chemistry of three aromatic herbicides are presented in Chapter 4, along with proposed oxidation mechanisms and products. Experiments were performed in an Oxidative Flow Reactor (OFR) coupled to a switching reagent ion CIMS, for a non-targeted approach for pesticide oxidation product detection. Pesticide oxidation followed typical OH oxidation mechanisms (OH abstraction with subsequent peroxide formation, OH addition to aromatic systems). MCPA and Mecoprop-p reaction rate constants with OH radical were estimated and used to calculate their atmospheric lifetimes (3 and 5 days, respectively). Newly identified products from MCPA and triclopyr oxidation are potentially harmful to the environment and to humans. Lastly, Chapter 5 covers oxidation of two nitrogen containing herbicides, trifluralin and acetochlor and mechanisms with proposed products are shown. Trifluralin photolyzed to produce NOx, and both herbicides produced isocyanic acid (HNCO) upon OH oxidation, an atmospheric toxin.Item Open Access Observations of acyl peroxy nitrates during the Front Range air pollution and photochemistry éxperiment (FRAPPÉ)(Colorado State University. Libraries, 2016) Zaragoza, Jake, author; Fischer, Emily V., advisor; Collett, Jeffrey L., committee member; Farmer, Delphine, committee memberThe Colorado Front Range is an ozone (O3) nonattainment region. The photochemistry of the region is influenced by emissions from the urban and oil and gas sectors, the complex terrain, and the meteorology. The Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) was a field intensive carried out in the Colorado Front Range during summer 2014 to characterize the regional chemical environment. Acyl peroxy nitrates (PANs) play important roles in atmospheric chemistry, acting as either sinks or sources for nitrogen oxides (NOx) depending on conditions. PANs and other trace gas species were measured at the Boulder Atmospheric Observatory (BAO) during FRAPPÉ. Situated at the southwestern edge of the Denver-Julesburg Basin and 35 km north of Denver, BAO has been the site of multiple field studies aiming to characterize the influence of emissions from the oil and gas sector. Here we focus on an analysis of the PANs measurements from BAO during FRAPPÉ. In particular, we focus on peroxyacetic nitric anhydride (PAN, CH3C(O)O2NO2), peroxymethacrylic nitric anhydride (MPAN, CH2C(CH3)C(O)O2NO2) and peroxypropionic nitric anhydride (PPN, CH3CH2C(O)O2NO2). Mean and maximum PAN mixing ratios (5-minute point) were 275 and 1519 pptv respectively. There were four days during FRAPPÉ where the observed PAN abundance exceeded 1 ppbv. These days were examined using FLEXible PARTicle dispersion model (FLEXPART) back trajectories in order to determine air mass origin. The high PAN days occurred when air masses were recirculating in the region, often under Denver Cyclones. However, a visual inspection of FLEXPART trajectories throughout FRAPPÉ showed that recirculation events in the region occurred on days with high (>1 ppbv), moderate (500 pptv − 1 ppbv), and low (<500 pptv) afternoon PAN mixing ratios. The PPN/PAN ratio observed at the BAO tower during the summer of 2014 was 21%, which suggests anthropogenically enhanced photochemical activity. The ratio was very consistent (R2 = 92%) and not dependent on wind direction, potentially reflecting a lack of variability in regional non-methane volatile organic compound (NMVOC) chemistry. The MPAN/PAN ratio was <5%, indicating that isoprene oxidation had very little influence on photochemistry compared to many other regions in the U.S. The relative abundances of PPN and MPAN were used to estimate the contribution of isoprene oxidation to local O3 production. It was found that the contribution to local O3 from isoprene oxidation was consistently less than 20%. The findings of this study suggest that anthropogenic emissions are the key drivers of PANs and O3 formation in the region.Item Open Access Quantifying commuter exposures to volatile organic compounds(Colorado State University. Libraries, 2014) Kayne, Ashleigh, author; Volckens, John, advisor; Peel, Jennifer, committee member; Collett, Jeffrey L., committee memberMotor-vehicles can be a predominant source of air pollution in cities. Traffic-related air pollution is often unavoidable for people who live in populous areas. Commuters may have high exposures to traffic-related air pollution as they are close to vehicle tailpipes. Volatile organic compounds (VOCs) are one class of air pollutants of concern because exposure to VOCs carries risk for adverse health effects. Specific VOCs of interest for this work include benzene, toluene, ethylbenzene, and xylenes (BTEX), which are often found in gasoline and combustion products. Although methods exist to measure time-integrated personal exposures to BTEX, there are few practical methods to measure a commuter's time-resolved BTEX exposure which could identify peak exposures that could be concealed with a time-integrated measurement. This study evaluated the ability of a photoionization detector (PID) to measure commuters' exposure to BTEX using Tenax TA samples as a reference and quantified the difference in BTEX exposure between cyclists and drivers with windows open and closed. To determine the suitability of two measurement methods (PID and Tenax TA) for use in this study, the precision, linearity, and limits of detection (LODs) for both the PID and Tenax TA measurement methods were determined in the laboratory with standard BTEX calibration gases. Volunteers commuted from their homes to their work places by cycling or driving while wearing a personal exposure backpack containing a collocated PID and Tenax TA sampler. Volunteers completed a survey and indicated if the windows in their vehicle were open or closed. Comparing pairs of exposure data from the Tenax TA and PID sampling methods determined the suitability of the PID to measure the BTEX exposures of commuters. The difference between BTEX exposures of cyclists and drivers with windows open and closed in Fort Collins was determined. Both the PID and Tenax TA measurement methods were precise and linear when evaluated in the laboratory using standard BTEX gases. The LODs for the Tenax TA sampling tubes (determined with a sample volume of 1,000 standard cubic centimeters which is close to the approximate commuter sample volumes collected) were orders of magnitude lower (0.04 to 0.7 parts per billion (ppb) for individual compounds of BTEX) compared to the PIDs' LODs (9.3 to 15 ppb of a BTEX mixture), which makes the Tenax TA sampling method more suitable to measure BTEX concentrations in the sub-parts per billion (ppb) range. PID and Tenax TA data for commuter exposures were inversely related. The concentrations of VOCs measured by the PID were substantially higher than BTEX concentrations measured by collocated Tenax TA samplers. The inverse trend and the large difference in magnitude between PID responses and Tenax TA BTEX measurements indicates the two methods may have been measuring different air pollutants that are negatively correlated. Drivers in Fort Collins, Colorado with closed windows experienced greater time-weighted average BTEX exposures than cyclists (p: 0.04). Commuter BTEX exposures measured in Fort Collins were lower than commuter exposures measured in prior studies that occurred in larger cities (Boston and Copenhagen). Although route and intake may affect a commuter's BTEX dose, these variables are outside of the scope of this study. Within the limitations of this study (including: small sample size, small representative area of Fort Collins, and respiration rates not taken into account), it appears health risks associated with traffic-induced BTEX exposures may be reduced by commuting via cycling instead of driving with windows closed and living in a less populous area that has less vehicle traffic. Although the PID did not reliably measure low-level commuter BTEX exposures, the Tenax TA sampling method did. The PID measured BTEX concentrations reliably in a controlled environment, at high concentrations (300-800 ppb), and in the absence of other air pollutants. In environments where there could be multiple chemicals present that may produce a PID signal (such as nitrogen dioxide), Tenax TA samplers may be a better choice for measuring BTEX. Tenax TA measurements were the only suitable method within this study to measure commuter's BTEX exposure in Fort Collins, Colorado.Item Open Access Remote continental aerosol characteristics in the Rocky Mountains of Colorado and Wyoming(Colorado State University. Libraries, 2013) Levin, Ezra JT, author; Kreidenweis, Sonia M., advisor; Collett, Jeffrey L., committee member; van den Heever, Susan C., committee member; Ham, Jay, committee memberThe Rocky Mountains of Colorado and Wyoming enjoy some of the cleanest air in the United States, with few local sources of particulate matter or its precursors apart from fire emissions, windblown dust, and biogenic emissions. However, anthropogenic influences are also present with sources as diverse as the populated Front Range, large isolated power plants, agricultural emissions, and more recently emissions from increased oil and gas exploration and production. While long-term data exist on the bulk composition of background fine particulate matter at remote sites in the region, few long-term observations exist of aerosol size distributions, number concentrations and size resolved composition, although these characteristics are closely tied to important water resource issues through the potential aerosol impacts on clouds and precipitation. Recent modeling work suggests sensitivity of precipitation-producing systems to the availability of aerosols capable of serving as cloud condensation nuclei (CCN); however, model inputs for these aerosols are not well constrained due to the scarcity of data. In this work I present aerosol number and volume concentrations, size distributions, chemical composition and hygroscopicity measurements from long-term field campaigns. I also explore the volatility of organic material from biomass burning and the potential impacts on aerosol loading. Relevant aerosol observations were obtained in several long-term field studies: the Rocky Mountain Atmospheric Nitrogen and Sulfur study (RoMANS, Colorado), the Grand Tetons Reactive Nitrogen Deposition Study (GrandTReNDS, Wyoming) and as part of the Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen project (BEACHON, Colorado). Average number concentrations (0.04 < Dp < 20 μm) measured during the field studies ranged between 1000 - 2000 cm-3 during the summer months and decreased to 200 - 500 cm-3 during the winter. These seasonal changes in aerosol number concentrations were correlated with the frequency of events typical of new particle formation. Measured sub-micron organic mass fractions were between 70 - 90% during the summer months, when new particle formation events were most frequent, suggesting the importance of organic species in the nucleation or growth process, or both. Aerosol composition derived from hygroscopicity measurements indicate organic mass fractions of 50 - 60% for particles with diameters larger than 0.15 μm during the winter. The composition of smaller diameter particles appeared to be organic dominated year-round. High organic mass fractions led to low values of aerosol hygroscopicity, described using the κ parameter. Over the entire year-long BEACHON study, κ had an average value of 0.16 ± 0.08, similar to values determined during biologically active periods in tropical and boreal forests, and lower than the commonly assumed value of κcontinental = 0.3. There was also an observed increase in κ with size, due to external mixing of the fine mode aerosol. Incorrect representations of κ or its size dependence led to erroneous values of calculated CCN concentrations, especially for supersaturation values less than 0.3%. At higher supersaturations, most of the measured variability in CCN concentrations was captured by changes in total measured aerosol number concentrations. While data from the three measurement sites were generally well correlated, indicating similarities in seasonal cycles and in total number concentrations, there were some variations between measurements made at different sites and during different years that may be partly due to the effects of local emissions. The averaged data provide reasonable, observationally-based parameters for modeling of aerosol number size distributions and corresponding CCN concentrations. Field observations clearly indicated the episodic influence of wildfire smoke on particle number concentrations and compositions. However, the semi-volatile nature of the organic carbon species emitted makes it difficult to predict how much of the emitted organic mass will remain in the condensed phase downwind. To better constrain the volatility of organic species in smoke, emissions from laboratory biomass combustion experiments were subjected to quantified dilution, resulting in reduction of aerosol mass concentrations over several orders of magnitude and a corresponding volatilization response of the organic particles that was fit to the commonly-applied Volatility Basis Set. Organic emissions from all burns with initial organic aerosol concentrations greater than 1000 μg m-3 contained material with saturation concentration values ranging between 1 and 10,000 μg m-3, with most of the organic mass falling at the two extremes of this range. For most burns, a single distribution was able to capture the volatility behavior of the organic material, within experimental uncertainty, despite the considerable variability in fuel and fire characteristics, suggesting that a simplified two-product model of gas-aerosol partitioning may be adequate to describe the evolution of biomass burning organic aerosol in models.Item Open Access Satellite constraints on surface concentrations of particulate matter(Colorado State University. Libraries, 2015) Ford Hotmann, Bonne, author; Heald, Colette L., advisor; Kreidenweis, Sonia M., committee member; Peel, Jennifer L., committee member; Collett, Jeffrey L., committee memberBecause of the increasing evidence of the widespread adverse effects on human health from exposure to poor air quality and the recommendations of the World Health Organization to significantly reduce PM2.5 in order to reduce these risks, better estimates of surface air quality globally are required. However, surface measurements useful for monitoring particulate exposure are scarce, especially in developing countries which often experience the worst air pollution. Therefore, other methods are necessary to augment estimates in regions with limited surface observations. The prospect of using satellite observations to infer surface air quality is attractive; however, it requires knowledge of the complicated relationship between satellite-observed aerosol optical depth (AOD) and surface concentrations. This dissertation explores how satellite observations can be used in conjunction with a chemical transport model (GEOS-Chem) to better understand this relationship. First, we investigate the seasonality in aerosols over the Southeastern United States using observations from several satellite instruments (MODIS, MISR, CALIOP) and surface network sites (IMPROVE, SEARCH, AERONET). We find that the strong summertime enhancement in satellite-observed aerosol optical depth (factor 2-3 enhancement over wintertime AOD) is not present in surface mass concentrations (25-55% summertime enhancement). Goldstein et al. [2009] previously attributed this seasonality in AOD to biogenic organic aerosol; however, surface observations show that organic aerosol only accounts for ~35% of PM2.5 mass and exhibits similar seasonality to total surface PM2.5. The GEOS-Chem model generally reproduces these surface aerosol measurements, but under represents the AOD seasonality observed by satellites. We show that seasonal differences in water uptake cannot sufficiently explain the magnitude of AOD increase. As CALIOP profiles indicate the presence of additional aerosol in the lower troposphere (below 700 hPa), which cannot be explained by vertical mixing; we conclude that the discrepancy is due to a missing source of aerosols above the surface layer in summer. Next, we examine the usefulness of deriving premature mortality estimates from "satellite-based" PM2.5 concentrations. In particular, we examine how uncertainties in the model AOD-to-surface-PM2.5 relationship, satellite retrieved AOD, and particulars of the concentration-response function can impact these mortality estimates. We find that the satellite-based estimates suggest premature mortality due to chronic PM2.5 exposure is 2-16% higher in the U.S. and 4-13% lower in China compared to model-based estimates. However, this difference is overshadowed by the uncertainty in the methodology, which we quantify to be on order of 20% for the model-to- surface-PM2.5 relationship, 10% for the satellite AOD and 30-60% or greater with regards to the application of concentration response functions. Because there is a desire for acute exposure estimates, especially with regards to extreme events, we also examine how premature mortality due to acute exposure can be estimated from global models and satellite-observations. We find similar differences between model and satellite-based mortality estimates as with chronic exposure. However the range of uncertainty is much larger on these shorter timescales. This work suggests that although satellites can be useful for constraining model estimates of PM2.5, national mortality estimates from the two methods are not significantly different. In order to improve the efficacy of satellite-based PM2.5 mortality estimates, future work will need to focus on improving the model representation of the regional AOD-to-surface-PM2.5 relationship, reducing biases in satellite-retrieved AOD and advancing our understanding of personal and population-level responses to PM2.5 exposure.Item Open Access The impact of pine beetle infestation on monoterpene emissions and secondary organic aerosol formation in western North America(Colorado State University. Libraries, 2012) Berg, Ashley R., author; Heald, Colette L., advisor; Collett, Jeffrey L., committee member; Farmer, Delphine K., committee memberOver the last decade, an extensive beetle outbreak has impacted western North America resulting in the mortality of over 100,000 km2 of forest throughout British Columbia and the western United States. Climate change has aided the expansion and continuation of this beetle infestation for more than a decade as beetles survive milder winters and expand northward and to higher elevation areas. Studies have been conducted to investigate the impact of this disturbance on forest carbon stocks, beetle-fire interactions, and meteorological variables, as well as to affirm the importance of including beetle infestation in models. In recent years there has been increased interest in the impact of beetle mortality and attack on atmospheric composition. Numerous studies have demonstrated that insect attack can prompt elevated emissions of volatile organic compounds (VOCs) in a variety of plant and tree species, including mountain pine beetle attacking lodgepole pine, the main beetle-host combination in the current outbreak. These enhanced VOC emissions are likely a defense mechanism of the tree, consisting of increasing emissions of compounds that are toxic to the beetles and attract predators of the beetles as well as increasing sap flow to help remove beetles from the trunk. This impact has not yet been modeled; however, beetle attack may have a significant impact on atmospheric composition and air quality in western North America. In this study, we use 14 years of beetle mortality data for 13 beetle species and beetle-induced monoterpene concentration data in the NCAR Community Earth System Model (CESM) to investigate the impact of beetle mortality and attack on monoterpene emissions and secondary organic aerosol (SOA) formation in western North America. Needleleaf vegetation is decreased each year based on the annual mortality data while emissions of certain compounds in needleleaf trees under attack are scaled-up based on recent beetle-induced VOC data for lodgepole pine (pine scenario) and Engelmann spruce (spruce scenario). As the mountain pine beetle has had the most extensive impact on mortality, we compare changes in emissions of VOCs and subsequent SOA formation caused by the mountain pine beetle to changes caused by the other 12 beetles combined. Beetle infestation impacts monoterpene emissions through both decreased emissions as trees are killed off (mortality effect) and increased emissions in trees under attack (attack effect). Regionally, beetle infestation may have a significant impact on monoterpene emissions and SOA concentrations with up to a 4-fold increase in monoterpene emissions and up to a 40% increase in SOA concentrations in some years. Responses to beetle attack can vary greatly over space and time as the areas affected as well as the magnitude of the impact depend on the extent of previous mortality and the number of trees under attack in a year. The model captures highly localized impacts on smaller-scales, while on larger-scales, the cumulative mortality effect often mutes the ongoing attack effect. The mountain pine beetle alone has an impact similar to that of the other 12 beetles combined, and the spruce scenario has an impact 3-4 times greater than the pine scenario due to differences in the magnitude of the observed enhancement in monoterpene emissions. In North America, the pine scenario would likely dominate since lodgepole pine is the main species impacted; however, smaller regions of spruce may see higher localized impacts on monoterpene emissions and SOA concentrations. Placed in the context of OM and PM2.5 IMPROVE network measurements, the changes in SOA concentrations due to beetle attack are in most cases small compared to the large annual and interannual variability in the measurements of total organic aerosol, indicating that most beetle-induced SOA changes are not likely detectable in current observation networks. However, in areas with especially large emissions enhancements (e.g. areas of spruce under attack) and lower variability in measurements of OM, beetle-induced changes in SOA may be observable. Due to the large potential impacts that beetle infestation may have on monoterpene emissions, SOA formation, and degradation of air quality, it is important that beetle infestation be included in future models.Item Open Access Tracking ammonia volatilization and fate from emission source to pristine ecosytem(Colorado State University. Libraries, 2014) Stratton, Joshua James, author; Borch, Thomas, advisor; Prieto, Amy, committee member; Bernstein, Elliott, committee member; Fisher, Ellen R., committee member; Collett, Jeffrey L., committee memberAmmonia has been widely documented as a contributor to negative impacts on natural ecosystems. Agricultural related management has been closely tied to ammonia emission and therefore negative impacts of ammonia pollution. The aim of this research is to improve our current understanding of how ammonia is lost from native and agricultural soils and if nitrogen isotopes can be used to elucidate what sources of ammonia pollution affect native ecosystems the most. Rocky Mountain National Park (RMNP) has undergone ecosystem changes due to excessive nitrogen deposition in the forms of ammonium, nitrate and organic nitrogen. Due to uncertainty in source apportionment; the efficacy of nitrogen isotopes of ammonia to distinguish sources of ammonia deposited in RMNP was investigated. This study shows average δ¹⁵N isotopes of certain sources (beef cattle, dairy cattle production, wastewater treatment, cropland, urban) were distinguishable at this study's emission sites; however, the average δ¹⁵N isotope values measured at a RMNP site were not useful for identification of specific ammonia sources. Supplemental information (weekly integrations of gaseous and particulate reduced nitrogen, oxidized nitrogen, sulfur measurements, and HYSPLIT modeling) was needed to help pinpoint the likely sources of ammonia, such as agriculture and biomass burning, affecting RMNP. Moreover, this supplemental information was used to support the most likely reasons δ¹⁵N isotope values observed in gaseous ammonia and wet deposition were indistinguishable compared to emission sources. Little is known about the potential local contribution of ammonia from soils within RMNP. Thus, the goal of this study was also to develop a method for analysis of ammonia emissions from intact soil cores sampled from a sub-alpine grassland and forest within RMNP. Nitrogen wet deposition was monitored at the sampling location to investigate possible impacts on soil emissions of ammonia. Lastly, method development and analysis of formation of ammonia (urea hydrolysis), pH speciation (ammonia and ammonium), and vapor pressure (Henry constant) were investigated in beef and dairy feedlots to reveal important controls on ammonia emission. This research provides new information on the importance of post emission physical and chemical processes, such as source mixing, isotopic fractionation, and dry deposition, preventing the use of δ¹⁵N isotopes for source tracking without the use of complementary techniques, such as atmospheric modeling. Moreover this work provides further evidence indicating that natural emissions within RMNP are not major sources of reduced nitrogen in the RMNP airshed. Lastly, this work provides new chemical values for the Henry constant, acid dissociation constant, and urea hydrolysis rate constants in animal production systems and can be used to better estimate ammonia emissions from animal production to improve our current emission inventories.