Browsing by Author "Fischer, Emily, advisor"
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Item Open Access Atmospheric and air quality implications of C2-C5 alkane emissions from the oil and gas sector(Colorado State University. Libraries, 2018) Tzompa Sosa, Zitely Asafay, author; Fischer, Emily, advisor; Kreidenweis, Sonia M., committee member; Pierce, Jeffrey, committee member; Jathar, Shantanu, committee memberEmissions of C2-C5 alkanes from the U.S. oil and gas sector have changed rapidly over the last decade. This dissertation quantifies the role of the oil and gas sector on light alkane emissions and abundances at local, regional, and global scales. First, we present an updated global ethane (C2H6) emission inventory based on 2010 satellite-derived CH4 fluxes with adjusted C2H6 emissions over the U.S. from the National Emission Inventory (NEI 2011). We contrast our global 2010 C2H6 emission inventory with one developed for 2001. The C2H6 difference between global anthropogenic emissions is subtle (7.9 versus 7.2 Tg yr-1), but the spatial distribution of the emissions is distinct. In the 2010 C2H6 inventory, fossil fuel sources in the Northern Hemisphere represent half of global C2H6 emissions and 95% of global fossil fuel emissions. Over the U.S., un-adjusted NEI 2011 C2H6 emissions produce mixing ratios that are 14-50 % of those observed by aircraft observations (2008-2014). When the NEI 2011 C2H6 emission totals are scaled by a factor of 1.4, the GEOS-Chem model largely reproduces a regional suite of observations, with the exception of the central U.S., where it continues to under- predict observed mixing ratios in the lower troposphere. Second, we use a nested GEOS-Chem simulation driven by updated 2011NEI emissions with aircraft, surface and column observations to 1) document spatial patterns in the emissions and observed atmospheric abundances of C2-C5 alkanes over the U.S., and 2) estimate the contribution of emissions from the U.S. oil and gas industry to these patterns. The oil and gas sector in the updated 2011NEI contributes >80% of the total U.S. emissions of C2H6 and propane (C3H8), and emissions of these species are largest in the central U.S. Observed mixing ratios of C2-C5 alkanes show enhancements over the central U.S. below 2 km. A nested GEOS-Chem simulation underpredicts observed C3H8 mixing ratios in the boundary layer over several U.S. regions and the relative underprediction is not consistent, suggesting C3H8 emissions should receive more attention moving forward. Our decision to consider only C4-C5 alkane emissions as a single lumped species produces a geographic distribution similar to observations. Due to the increasing importance of oil and gas emissions in the U.S., we recommend continued support of existing long-term measurements of C2-C5 alkanes. We suggest additional monitoring of C2-C5 alkanes downwind of northeastern Colorado, Wyoming and western North Dakota to capture changes in these regions. The atmospheric chemistry modeling community should also evaluate whether chemical mechanisms that lump ≤ C6 alkanes are sufficient to understand air quality issues in regions with large emissions of these species. Finally, we investigate the contribution of C2-C5 alkane emissions from the U.S. oil and gas industry to O3 abundances at regional and global scales. Emissions of C2-C5 alkanes from the oil and gas sector make the largest contribution to ozone (O3) production over the central U.S. compared to other regions. The Colorado Front Range is the 8-hour O3 non-attainment area with the highest summertime daytime average O3 enhancement attributed to the U.S. oil and gas sector. The global tropospheric contribution of C2-C5 alkane emissions from the U.S. oil and gas sector to the O3 burden is 0.5 Tg for the year 2011, which represents 0.27% of the Northern Hemisphere tropospheric O3 burden.Item Embargo Changes in shortwave solar radiation under local and transported wildfire smoke plumes: implications for agriculture, solar energy, and air quality applications(Colorado State University. Libraries, 2024) Corwin, Kimberley A., author; Fischer, Emily, advisor; Pierce, Jeffrey, committee member; Chiu, Christine, committee member; Corr-Limoges, Chelsea, committee member; Burkhardt, Jesse, committee memberThe emission and transport of pollutants from wildfires is well-documented, particularly at the surface. However, smoke throughout the atmospheric column affects incoming shortwave solar radiation with potentially wide-ranging consequences. By absorbing and scattering light, smoke changes the amount and characteristics of shortwave radiation–a resource that controls plant photosynthesis, solar energy generation, and atmospheric photochemical reactions. In turn, these influence ecological systems as well as air quality and human health. This dissertation examines how wildfire smoke alters boundary layer and surface-level shortwave radiation in ways that are relevant for agricultural, energy, and air quality applications. First, I present an analysis of smoke frequency and smoke-driven changes in the total and diffuse fraction (DF) of photosynthetically active radiation (PAR; 400-700 nm) at the surface. I compare PAR and PAR DF on smoke-impacted and smoke-free days during the agricultural growing season from 2006 to 2020 using data from 10 ground-based radiation monitors and satellite-derived smoke plume locations. I show that, on average, 20% of growing season days are smoke-impacted and that smoke prevalence has increased over time (r = 0.60, p < 0.05). Smoke frequency peaks in the mid to late growing season (i.e., July, August), particularly over the northern Rocky Mountains, Great Plains, and Midwest. I find an increase in the distribution of PAR DF on smoke-impacted days, with larger increases at lower cloud fractions. On clear-sky days, daily average PAR DF increases by 10 percentage points when smoke is present. Spectral analysis of clear-sky days shows smoke increases DF (average: +45%) and decreases total irradiance (average: −6%) across six wavelengths measured from 368 to 870 nm. Optical depth measurements from ground and satellite observations both indicate that spectral DF increases and total spectral irradiance decreases with increasing smoke plume optical depth. My analysis provides a foundation for understanding smoke's impact on PAR, which carries implications for agricultural crop productivity under a changing climate. Second, I examine smoke's impact on two key measures used to assess a location's baseline solar resource availability for solar energy production: direct normal (DNI) and global horizontal (GHI) irradiance. I quantify smoke-driven changes in DNI and GHI at different spatial and temporal scales across the contiguous U.S. (CONUS) using radiative transfer model output and satellite-based smoke, aerosol, and cloud observations. Importantly, I expand the scale of previous studies on smoke and solar energy by including areas primarily affected by dilute, aged, transported smoke plumes in addition to areas with dense, fresh, local smoke plumes. I show that DNI and GHI decrease as smoke frequency increases at the state, regional, and national scale. DNI is more sensitive to smoke with sizable losses persisting downwind of fires. Although large reductions in GHI are possible close to fires, mean GHI declines minimally (< 5%) due to transported smoke. Overall, GHI–the main resource used for photovoltaic energy production–remains a relatively stable resource across most of CONUS even in extreme fire seasons, which is promising given U.S. solar energy goals. Third, I investigate smoke-driven changes in surface-level and boundary layer downwelling actinic flux (F↓)–a crucial component of determining the rate of photooxidation in the atmosphere. I present a case study of changes in F↓ at 550 nm (process validation) and 380 nm (NO2 photolysis) along a research flight through the California Central Valley during the 2018 Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN) aircraft campaign. F↓ was measured onboard via the HIAPER Airborne Radiation Package (HARP), and I use the National Center for Atmospheric Research (NCAR) Tropospheric Ultraviolet and Visible (TUV) Radiation Model to compute F↓ under smoke-free and smoke-impacted conditions. Modeling F↓ with TUV facilitates calculating the change in F↓ and provides a means of assessing F↓ at altitudes not sampled by the aircraft, such as the ground. I find that the smoke-impacted F↓ from TUV aligns closely with HARP observations: all modeled fluxes are within 20% of measurements at 550 nm and 85% are within 20% of measurements at 380 nm. The average modeled-to-measured ratios (F ↓550=0.96; F ↓380=0.89) indicate that TUV minorly underestimates the observed F↓. On average, observed F↓380 decreased 26%, 17%, and 9% at 0-0.5 km, 0.5-1 km, and 1-1.5 km, respectively, while TUV estimates larger reductions of 41%, 26%, and 19% at the same altitudes. At the ground-level, I calculate a 47% decrease in F↓380 using TUV, which is likely an upper bound given the model slightly underestimates observations. As wildfire smoke increases with climate change, understanding how smoke aloft changes photochemistry is increasingly important for constraining future air quality.Item Open Access Inorganic gas-aerosol partitioning in and around animal feeding operation plumes in northeastern Colorado in late summer 2021(Colorado State University. Libraries, 2023) Li, En, author; Pierce, Jeffrey, advisor; Fischer, Emily, advisor; Jathar, Shantanu, committee member; Sullivan, Amy, committee memberAmmonia (NH3) from animal feeding operations (AFOs) is an important source of reactive nitrogen in the US, but despite its ramifications for air quality and ecosystem health, its near-source evolution remains understudied. To this end, Phase I of the Transport and Transformation of Ammonia (TRANS2Am) field campaign was conducted in the northeastern Colorado Front Range in summer 2021 and characterized atmospheric composition downwind of AFOs during 10 research flights. Airborne measurements of NH3, nitric acid (HNO3), and a suite of water-soluble aerosol species collected onboard the University of Wyoming King Air (UWKA) research aircraft present a unique opportunity to investigate the sensitivity of particulate matter (PM) formation to AFO emissions. We couple the observations with thermodynamic modeling to predict the seasonality of ammonium nitrate (NH4NO3) formation. We find that during TRANS2Am northeastern Colorado is consistently in the NH3-rich and HNO3-limited NH4NO3 formation regime. Further investigation using the Extended Aerosol Inorganics Model (E-AIM) reveals that summertime temperatures (mean: 23 ˚C) of northeastern Colorado, especially near the surface, inhibit NH4NO3 formation despite high NH3 concentrations (max: ≤ 114 ppbv). Lastly, we model and winter conditions to explore the seasonality of NH4NO3 formation and find that cooler temperatures could support substantially more NH4NO3 formation. Whereas summertime NH4NO3 only exceeds 1 µg m-3 ~10% of the time in summer, modeled NH4NO3 would exceed 1 µg m-3 61% (88%) of the time in spring/autumn (winter), with a 10°C (20°C) temperature decrease relative to the campaign.Item Open Access Investigating emissions and evolution of reactive nitrogen in western U.S. wildfire smoke plumes(Colorado State University. Libraries, 2020) Lindaas, Jakob, author; Fischer, Emily, advisor; Ravishankara, A. R., committee member; Collett, Jeffrey, Jr., committee member; Jathar, Shantanu, committee memberWildfires are an important source of reactive nitrogen (Nr) to the atmosphere. Large wildfires are becoming more frequent in the western U.S. and smoke from large western U.S. wildfires is becoming a proportionately larger driver of poor air quality in certain U.S. regions. Nr in smoke contributes to the production of ozone (O3), the formation of secondary inorganic and organic aerosol, and nitrogen deposition to downwind ecosystems, with attendant negative impacts on human and ecosystem health and important consequences for the earth's radiative budget. Smoke from wildfires is difficult to sample though, since it is hard to predict exactly where fires will start and which fires will grow larger across the western U.S. Scientific aircraft are able to sample smoke where and when it occurs, making them ideal platforms from which to gather observations of gases and particles in smoke. This dissertation presents results from three analyses investigating the emissions and evolution of reactive nitrogen in wildfire smoke using data from the Western wildfires Experiment on Cloud chemistry, Aerosol absorption, and Nitrogen (WE-CAN). The WE-CAN field intensive sampled fresh smoke from 23 identified large wildfires in the western U.S. during August and September 2018. Pseudo-Lagrangian ("lawn-mower pattern") sampling was accomplished for about half of these fires, meaning that the plane was able to intercept the same smoke multiple times as it was transported downwind. Additionally, mixed and older smoke from indeterminate sources was sampled in the free troposphere as well as in the California Central Valley where it mixed with anthropogenic emissions. These data represent a large increase in the number of western wildfire smoke plumes intercepted by research aircraft in a systematic fashion. First, I present a general overview of Nr emissions from 16 wildfires using a large cross section of the suite of chemical and physical measurements made onboard the National Science Foundation/National Center for Atmospheric Research (NSF/NCAR) C-130 aircraft. I find that reduced N compounds generally make up more than half of the total measured Nr (∑Nr) (39 - 80%, median = 66%). This was not necessarily expected since we sampled plumes from fires at their most active time of day, with assumed burning conditions that favored emission of oxidized forms of Nr. I observe evidence of rapid chemistry in the minutes between emission and the first sampling periods in all fires via significant abundances of peroxyacetic nitric anhydride (PAN) even in these youngest plume samples. I find evidence for the influence of both combustion conditions and fuel N content influencing the ratio of the sum of measured ammonia (NH3) plus particulate ammonium (pNH4) and the sum of oxidized nitrogen (∑NHx/∑NOy). Finally, estimated emission factors (EF) from these fires can be compared with previous literature for similar fuel types, with NH3 EFs similar to or higher than previous lab and field observations, and NOx EFs generally lower than previous estimates. Next I explore the evolution of NH3 in fresh and aged smoke. Focusing on 8 pseudo-Lagrangian sampled plumes, I observe e-folding loss timescales for NH3 with respect to gas-particle partitioning on the order of minutes to hours, similar to previous estimates in fresh smoke. I find empirical evidence for the association of NH3 and nitric acid (HNO3) to form ammonium nitrate (NH4NO3), though not all plumes contain conditions favorable to NH4NO3 formation. Fresh, dense plumes injected at higher altitudes (and lower temperatures) are more likely to favor NH4NO3 formation, a conclusion consistent with previous model simulations in the literature. Measured organic acid ions also suggest the presence of NH4-organic salts in the plumes sampled. Finally, I also use observations collected in medium and old aged smoke to find additional evidence for the formation of NH4NO3 in plumes injected higher in the atmosphere with larger oxidized N to NH3 ratios. Lastly, I investigate the production of PAN and peroxypropionic nitric anhydride (PPN) in the same set of pseudo-Lagrangian sampled plumes. Increases in dilution-corrected PAN and PPN mixing ratios in all plumes suggest that PAN and PPN are produced in all smoke plumes sampled, with the rate of increase similar to the handful of previous observations. I then use a simple observation-based model to determine the dominant precursors of PAN and PPN in fresh smoke plumes. From the model I infer that acetaldehyde is the dominant immediate PAN precursor in large western wildfire smoke plumes, with biacetyl also serving as an important precursor. To my knowledge this is the first time these conclusions have been drawn for smoke from an observational framework and it suggests that biacetyl should be included in models of smoke plume evolution. With respect to PPN, I find that propanal is an important immediate PPN precursor in fresh wildfire smoke. Unexpectedly, I also find that at least one other immediate PPN precursor is likely needed to explain PPN production, and suggest that this precursor may be ethylglyoxal. However, very few in situ measurements of ethylglyoxal exist to test this hypothesis.Item Open Access Ketones in the troposphere: studies of loss processes, emissions, and production(Colorado State University. Libraries, 2020) Brewer, Jared F., author; Fischer, Emily, advisor; Ravishankara, A. R., advisor; Barnes, Elizabeth, committee member; Jathar, Shantanu, committee memberKetones play an important role in atmospheric chemistry of the troposphere because they are oxidized VOCs that are both relatively abundant with sufficiently long-lifetimes to be distributed regionally. Ketone photolysis is a potentially important source of HOx radicals in the upper troposphere; it can also serve as a source of peroxy radicals which contribute to the formation of peroxy acyl nitrate-type (PAN-type) compounds. My thesis focuses on the atmospheric processes and budgets of smaller ketones. In this thesis, we discuss a series of four studies aimed at understanding the importance of atmospheric ketones to production of oxidants and PAN-type compounds. The four studies covered here involve laboratory measurements, interpretation of atmospheric observations, and modeling calculations. Chapter 2 of this thesis discusses an update to and global sensitivity analysis of the global budget of acetone. We test how sensitive a global simulation of acetone is to literature-derived ranges of input factors used to represent 1) direct emissions and secondary natural sources of acetone from the biosphere; 2) loss via photolysis; and 3) dry deposition. We use the Morris method (one-at-a-time variations) to identify and prioritize potential reasons for model-measurement differences for acetone. This study helps identify what specific processes and/or geographic regions deserve further attention via modeling and/or measurements to constrain the global budget of this species. Of the sources tested, acetone is globally most sensitive to the direct emissions from the biosphere, with other sources and sinks being important on a seasonal and regional basis. Chapter 3 presents the results of laboratory measurements of absorption cross sections of MEK and DEK (along with their uncertainties) measured in the laboratory between 200-335 nm at temperatures ranging from 242-320 K, with a spectral resolution of 1 nm. We also report absorption cross sections for PEK at the same resolution and wavelengths at 296 K. We present a simple "two-state" physically based model to understand the temperature variation of the cross sections and to extrapolate cross sections beyond the temperatures of the measurements. The implementation of these temperature-dependent cross-sections is most important in the colder upper troposphere, where this work suggests a ~20% decrease in MEK photolysis rate relative to the previous understanding. In Chapter 4, we present an analysis of aircraft observations of MEK in the remote marine troposphere from the Atmospheric Tomography (ATom) project. We show that the observed vertical profiles over clean oceans suggests an oceanic source of MEK. We show that the ocean serves as a source of MEK to the atmosphere during both meteorological winter and summer. MEK in clean marine air over the remote oceans correlates with both acetone and acetaldehyde, whose primary sources in the ocean water are the photooxidation of organic material. Finally, in Chapter 5, we bring together the information gathered from Chapters 2 and 3 to improve our ability to model MEK globally and, with these and other model improvements, present the first global budget of MEK. We discuss the magnitudes, distribution, and seasonality of the sinks, sources, and atmospheric mixing ratios of MEK as well. We also present a comparison of simulated MEK abundances using a suite of available aircraft observations of MEK from around the globe. Our results suggest that MEK is much less abundant in the atmosphere than acetone, but the fluxes of MEK into the atmosphere are about a tenth as those of acetone. The most important sources of MEK to the atmosphere are from the ocean and the oxidation of primarily anthropogenic alkanes, while the most important sinks of MEK are photolysis and oxidation by OH. We pull the information from all these four studies to show that our knowledge of the atmospheric role of acetone and MEK are improved. We also identify gaps in our knowledge that should be pursued to further improve quantifications of the roles of ketones in the troposphere.Item Open Access Planning for an unknown future: incorporating meteorological uncertainty into predictions of the impact of fires and dust on US particulate matter(Colorado State University. Libraries, 2019) Brey, Steven, author; Fischer, Emily, advisor; Barnes, Elizabeth, advisor; Pierce, Jeffrey, committee member; Rocca, Monique, committee memberExposure to particulate matter (PM) pollution has well documented health impacts and is regulated by the United States (U.S.) Environmental Protection Agency (EPA). In the U.S. wildfire smoke and wind-blown dust are significant natural sources of PM pollution. This dissertation shows how the environmental conditions that drive wildfires and wind-blown dust are likely to change in the future and what these changes imply for future PM concentrations. The first component of this dissertation shows how human ignitions and environmental conditions influence U.S. wildfire activity. Using wildfire burn area and ignition data, I find that in both the western and southeastern U.S., annual lightning- and human-ignited wildfire burn area have similar relationships with key environmental conditions (temperature, relative humidity, and precipitation). These results suggest that burn area for human- and lightning-ignited wildfires will be similarly impacted by climate change. Next, I quantify how the environmental conditions that drive wildfire activity are likely to change in the future under different climate scenarios. Coupled Model Intercomparison Project phase 5 (CMIP5) models agree that western U.S. temperatures will increase in the 21st century for representative concentration pathways (RCPs) 4.5 and 8.5. I find that averaged over seasonal and regional scales, other environmental variables demonstrated to be relevant to fuel flammability and aridity, such as precipitation, evaporation, relative humidity, root zone soil moisture, and wind speed, can be used to explain historical variability in wildfire burn area as well or better than temperature. My work demonstrates that when objectively selecting environmental predictors using Lasso regression, temperature is not always selected, but that this varies by western U.S. ecoregion. When temperature is not selected, the sign and magnitude of future changes in burn area become less certain, highlighting that predicted changes in burn area are sensitive to the environmental predictors chosen to predict burn area. Smaller increases in future wildfire burn area are estimated whenever and wherever the importance of temperature as a predictor is reduced. The second component of this dissertation examines how environmental conditions that drive fine dust emissions and concentrations in the southwestern U.S. change in the future. I examine environmental conditions that influence dust emissions including, temperature, vapor pressure deficit, relative humidity, precipitation, soil moisture, wind speed, and leaf area index (LAI). My work quantifies fine dust concentrations in the U.S. southwest dust season, March through July, using fine iron as a dust proxy, quantified with measurements from the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network between 1995 and 2015. I show that the largest contribution to the spread in future dust concentration estimates comes from the choice of environmental predictor used to explain observed variability. The spread between different environmental predictor estimates can be larger than the spread between climate scenarios or intermodel spread. Based on linear estimates of how dust concentrations respond to changes in LAI, CMIP5 estimated increases in LAI would result in reduced dust concentrations in the future. However, when I objectively select environmental predictors of dust concentrations using Lasso regression, LAI is not selected in favor of other variables. When using a linear combination of objectively selected environmental variables, I estimate that future southwest dust season mean concentrations will increase by 0.24 μg m−3 (12%) by the end of the 21st century for RCP 8.5. This estimated increase in fine dust concentration is driven by decreases in relative humidity, precipitation, soil moisture, and buffered by decreased wind speeds.