Mountain Scholar :: Browsing by Author "Pierce, Jeffrey, committee member"

Browsing by Author "Pierce, Jeffrey, committee member"

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Open Access
A low-cost monitor for simultaneous measurement of fine particulate matter and aerosol optical depth
(Colorado State University. Libraries, 2018) Wendt, Eric, author; Volckens, John, advisor; Jathar, Shantanu, committee member; Yalin, Azer, committee member; Pierce, Jeffrey, committee member
Exposure to airborne particulate matter with diameters less than 2.5 µm (PM2.5) is a leading cause of death and disease globally. In addition to affecting health, PM2.5 affects climate and atmospheric visibility. NASA currently uses satellite imaging technology to measure particulate matter air pollution across the world. Satellite image data are used to derive aerosol optical depth (AOD), which is the extinction of light in the atmospheric column. Although AOD data are often used to estimate surface PM2.5 concentration, there is considerable uncertainty associated with the relationship between satellite-derived AOD and ground-level PM2.5. Instruments known as Sun photometers can measure AOD from the Earth's surface and are often used for validation and calibration of satellite data. Reference-grade Sun photometers generally do not have co-located PM2.5 measurements and are too expensive to deploy in large numbers. The objective of this work was to develop an inexpensive and compact integrated PM2.5 mass and AOD sampler known as the Solar-Powered Aerosol Reference Calibrator (SPARC). PM2.5 is sampled using an ultrasonic pumping system, a size-selective cyclone separator, and a filter. Filter measurements can be used to correct the output from a low-cost direct-reading PM2.5 sensor housed within the SPARC. AOD is measured using optically filtered photodiodes at four discrete wavelengths. A suite of integrated sensors enable time-resolved measurement of key metadata including location, altitude, temperature, barometric pressure, relative humidity, solar incidence angle and spatial orientation. The AOD sensors were calibrated relative to a reference monitor in the Aerosol Robotics Network (AERONET). Field validation studies revealed close agreement for AOD values measured between co-located SPARC and AERONET monitors and for PM2.5 mass measured between co-located SPARC and EPA Federal Reference Method (FRM) monitors. These field validation results for this novel monitor demonstrate that AOD and PM2.5 can be accurately measured for the evaluation of AOD:PM2.5 ratios.
Open Access
Atmospheric and air quality implications of C2-C5 alkane emissions from the oil and gas sector
(Colorado State University. Libraries, 2018) Tzompa Sosa, Zitely Asafay, author; Fischer, Emily, advisor; Kreidenweis, Sonia M., committee member; Pierce, Jeffrey, committee member; Jathar, Shantanu, committee member
Emissions of C2-C5 alkanes from the U.S. oil and gas sector have changed rapidly over the last decade. This dissertation quantifies the role of the oil and gas sector on light alkane emissions and abundances at local, regional, and global scales. First, we present an updated global ethane (C2H6) emission inventory based on 2010 satellite-derived CH4 fluxes with adjusted C2H6 emissions over the U.S. from the National Emission Inventory (NEI 2011). We contrast our global 2010 C2H6 emission inventory with one developed for 2001. The C2H6 difference between global anthropogenic emissions is subtle (7.9 versus 7.2 Tg yr-1), but the spatial distribution of the emissions is distinct. In the 2010 C2H6 inventory, fossil fuel sources in the Northern Hemisphere represent half of global C2H6 emissions and 95% of global fossil fuel emissions. Over the U.S., un-adjusted NEI 2011 C2H6 emissions produce mixing ratios that are 14-50 % of those observed by aircraft observations (2008-2014). When the NEI 2011 C2H6 emission totals are scaled by a factor of 1.4, the GEOS-Chem model largely reproduces a regional suite of observations, with the exception of the central U.S., where it continues to under- predict observed mixing ratios in the lower troposphere. Second, we use a nested GEOS-Chem simulation driven by updated 2011NEI emissions with aircraft, surface and column observations to 1) document spatial patterns in the emissions and observed atmospheric abundances of C2-C5 alkanes over the U.S., and 2) estimate the contribution of emissions from the U.S. oil and gas industry to these patterns. The oil and gas sector in the updated 2011NEI contributes >80% of the total U.S. emissions of C2H6 and propane (C3H8), and emissions of these species are largest in the central U.S. Observed mixing ratios of C2-C5 alkanes show enhancements over the central U.S. below 2 km. A nested GEOS-Chem simulation underpredicts observed C3H8 mixing ratios in the boundary layer over several U.S. regions and the relative underprediction is not consistent, suggesting C3H8 emissions should receive more attention moving forward. Our decision to consider only C4-C5 alkane emissions as a single lumped species produces a geographic distribution similar to observations. Due to the increasing importance of oil and gas emissions in the U.S., we recommend continued support of existing long-term measurements of C2-C5 alkanes. We suggest additional monitoring of C2-C5 alkanes downwind of northeastern Colorado, Wyoming and western North Dakota to capture changes in these regions. The atmospheric chemistry modeling community should also evaluate whether chemical mechanisms that lump ≤ C6 alkanes are sufficient to understand air quality issues in regions with large emissions of these species. Finally, we investigate the contribution of C2-C5 alkane emissions from the U.S. oil and gas industry to O3 abundances at regional and global scales. Emissions of C2-C5 alkanes from the oil and gas sector make the largest contribution to ozone (O3) production over the central U.S. compared to other regions. The Colorado Front Range is the 8-hour O3 non-attainment area with the highest summertime daytime average O3 enhancement attributed to the U.S. oil and gas sector. The global tropospheric contribution of C2-C5 alkane emissions from the U.S. oil and gas sector to the O3 burden is 0.5 Tg for the year 2011, which represents 0.27% of the Northern Hemisphere tropospheric O3 burden.
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 member
The 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.
Open Access
Characteristics of atmospheric ice nucleating particles associated with biomass burning in the US: prescribed burns and wildfires
(Colorado State University. Libraries, 2013) McCluskey, Christina S., author; Kreidenweis, Sonia, advisor; DeMott, Paul, advisor; Pierce, Jeffrey, committee member; Volckens, John, committee member
Insufficient knowledge regarding the sources and number concentrations of atmospheric ice nucleating particles (INP) leads to large uncertainties in understanding the interaction of aerosols with cloud processes, such as cloud life time and precipitation rates. An increasingly important source of aerosol in the United States is biomass burning, particularly in the form of prescribed burns and wildfires in the southeastern and western U.S., respectively. Prior field and laboratory observations have suggested that biomass burning can be a source of INP. However, emissions from biomass burning are complex, varying with combustion efficiency, fuel type, plume age and dilution. Thus, this potentially important source of INP is poorly characterized. This study utilizes measurements of INP from a diverse set of biomass burning events to better understand INP associated with biomass burning in the U.S. Prescribed burns in Georgia and Colorado, two Colorado wildfires and two laboratory burns were monitored for INP number concentrations (nINP) using the Colorado State University continuous-flow diffusion chamber (CFDC) to activate INP in the condensation/immersion freezing nucleation mode. Additional measurements included total particle number concentrations, number concentrations of particles with diameters larger than 500 nm, aerosol mass concentrations, carbon monoxide concentrations and chemically-speciated bulk aerosol filter samples. Additionally, activated INP were collected onto TEM grids downstream of the CFDC, isolating INP for single particle chemical and morphological analyses. These fires varied by fuel type, including wiregrass, longleaf pine and ponderosa pine, and also varied by combustion efficiency, ranging from highly flaming to a mixture of flaming and smoldering. Additionally, plume histories were different between the fires including aged plumes from the wildfires and freshly emitted smoke from the prescribed and laboratory burns. The relationship between nINP and total particle number concentrations, evident within prescribed burning plumes, was degraded within aged smoke plumes from the wildfires, limiting the utility of this relationship for comparing laboratory and field data. Larger particles, represented by n500nm, are less vulnerable to plume processing and have previously been evaluated for their relation to nINP. Our measurements indicated that for a given n500nm, nINP associated with the wildfires were nearly an order of magnitude higher than nINP found in prescribed fire emissions. That is, nINP represented a much larger fraction of n500nm in wildfires as compared with prescribed fires. Further, an existing parameterization for "global" nINP that relates INP abundance to n500nm largely under-predicted and over-predicted nINP emitted from wildfires and prescribed burns, respectively. Reasons for the differences between INP characteristics in these emissions were explored, including variations in combustion efficiency, fuel type, transport time and environmental conditions. Combustion efficiency and fuel type were eliminated as controlling factors by comparing samples with contrasting combustion efficiencies and fuel types. Transport time was eliminated because the expected impact would be to reduce n500nm, thus resulting in the opposite effect from the observed change. Bulk aerosol chemical composition analyses support the potential role of elevated soil dust particle concentrations during the fires, contributing to the population of INP, but the bulk analyses do not target INP composition directly. Predictions from the Naval Aerosol Analysis and Prediction System model further indicate elevated dust mass concentrations during the wildfire periods, suggesting impact of mineral dust from long-range transport (LRT). It is hypothesized that both hardwood burning and soil lofting are responsible for the elevated production of INP in the Colorado wildfires in addition to LRT of mineral dust. The chemical compositions of INP were probed directly via TEM imaging. Single particle analyses of residual INP showed that they comprised various C-containing particle types, but with a higher abundance of mineral and metal oxide containing INP in emissions from flaming phase combustion. Fractal soot was found as an INP type comprising up to 60% of collected INP in young smoke emissions from the Georgia prescribed burns. In a series of laboratory combustion experiments, the use of a new instrumental set up, pairing the CFDC with a single particle soot photometer, revealed up to a 60% decrease in active INP after the removal of refractory black carbon from smoke aerosol emitted from a highly flaming burn of wiregrass, supporting that soot particles serve as INP in fire emissions. The presence of soil minerals was clearly evident in TEM images of samples taken during the wildfires in addition to tarballs, carbon balls most commonly associated with aged smoke plumes. These results demonstrate that the ice nucleating particles observed in the wildfires were influenced by other factors not represented in the smoke emitted from the laboratory or prescribed burns. Finally, an INP parameterization was developed based on the temperature dependent relationship between nINP and n500nm, following methods used by previous studies. This parameterization is likely only representative of the Hewlett and High Park wildfires due to the apparent impact of non-biomass-burning aerosol. However, all wildfires are typically associated with vigorous localized convection and arid soils, required for the lofting of the soils and dusts similar to these wildfires. It will be useful to compare future wildfires in various regions to the proposed parameterization.
Open Access
Constraining marine ice nucleating particle parameterizations in atmospheric models using observations from the Southern Ocean
(Colorado State University. Libraries, 2020) Moore, Kathryn A., author; Kreidenweis, Sonia, advisor; DeMott, Paul, advisor; Farmer, Delphine, committee member; Pierce, Jeffrey, committee member
The limited anthropogenic and terrestrial aerosol sources impacting the Southern Ocean (SO) make it a unique site to study the production of primary sea spray aerosols (SSA) and their role in modifying cloud properties. Previous observations of low ice nucleating particle (INP) concentrations and recent modeling work support the idea that the SO INP population is dominated by SSA. These marine INPs are hypothesized to strongly influence the lifetime, formation, and optical properties of the supercooled and mixed phase clouds that are common in the region, though direct observational evidence for this is lacking. This study focuses on improving our understanding of INP emissions in the marine boundary layer over the SO, with applicability to other ocean regions, and to provide in situ measurements with which to validate and improve INP parameterizations in global and cloud resolving models. Measurements of INPs and aerosols in the marine boundary layer were made during the Clouds, Aerosols, Precipitation Radiation and atmospherIc Composition Over the southeRN ocean 2 (CAPRICORN-2) study on the R/V Investigator during Jan. - March 2018. An initial focus of this thesis was on increasing speed and reproducibility of processing online INP measurements, as well as improving the determination of statistical significance and uncertainty bounds. Different approaches to parameterizing INPs in models are explored for SO aerosols, including the use of aerosol surface area and number concentrations. With an eye towards augmenting global datasets of INPs, a comparison of particle surface area measurements from four different techniques is presented, for use in developing and testing INP parameterizations for different sources and atmospheric conditions. Surface area concentrations derived from Wideband Integrated Bioaerosol Sensor (WIBS) and nephelometer observations are strongly correlated with direct particle size distribution measurements, and can be used in their stead. Uncertainty bounds for both techniques and a scaling factor for WIBS measurements are provided to aid in these estimates. INP concentrations observed during CAPRICORN-2 are very low across the entire temperature range measured (to -30 °C), even compared to previous measurements of marine-dominated airmasses. Unlike INPs from other sources, Southern Ocean marine INPs appear most correlated with accumulation, rather than coarse mode, particles, and are dominated by submicron particles. Commonly used relationships between coarse mode particle number and total aerosol surface area show no significant correlation with SO INP concentrations, indicating a different functional form or different independent variable may be needed to accurately parameterize marine INPs in models.
Open Access
Development and validation of an outdoor low-cost smoke monitor
(Colorado State University. Libraries, 2017) Kelleher, Scott, author; Volckens, John, advisor; Jathar, Shantanu, committee member; Anderson, Georgiana Brooke, committee member; Pierce, Jeffrey, committee member
Wildfires and prescribed fires produce emissions that are harmful to human health. These health effects, however, are difficult to quantify, likely in part due to sparse data on exposure. The ability to measure fire emissions as they reach sensitive areas is critical to ensuring the protection of public health. Ground level quantification of smoke from wildfires and prescribed fires has proven to be a difficult task. The state of the art for monitoring outdoor air quality has long relied upon expensive, cumbersome equipment that generally requires line power. Few ground-based measurements are typically made during fire events, which limits our ability to quantify and assess the impact of smoke from fire events. The objective of this work was to develop and validate a new type of outdoor air quality monitor, the Outdoor Aerosol Sampler (OAS). The OAS is an active, filter-based air sampler that has been miniaturized and weatherproofed. The OAS represents and attempt to address the technical limitations of field sampling with a device that is relatively inexpensive and independently powered. Prototype development of the OAS was made possible through low-cost electronics, open-source programming platforms, and in house fabrication methods. An online PM2.5 sensor was selected and integrated with the OAS. A Monte Carlo simulation aided in the selection of battery and solar power necessary to independently power the OAS, while keeping cost and size to a minimum. Cellular communications established via Short Message Service (SMS) technology were utilized in transmitting online sensor readings and controlling the OAS remotely. Numerous OAS were deployed to monitor smoke concentrations downwind from a large prescribed fire. Mass concentrations sampled from the burn were interpolated to depict smoke concentration gradients downwind of the fire. Field tests found OAS solar charging efficiency (6.7%) to be slightly less than model input efficiency (7.5%). Outdoor urban testing of the OAS demonstrates moderate agreement with equivalent federal reference method samplers for gravimetric analysis of PM2.5.
Open Access
Development of mobile open-path cavity ring-down spectrometer for measurement of trace atmospheric methane gas
(Colorado State University. Libraries, 2018) McHale, Laura, author; Yalin, Azer P., advisor; Marchese, Anthony, committee member; Olsen, Daniel, committee member; Pierce, Jeffrey, committee member
Use in recent decades of methane as a 'clean' alternative to coal and gasoline has seen a rapid increase in natural gas extraction in the United States. Although combustion of methane produces less CO2 than traditional fuels, it is a powerful greenhouse gas with a 20 year Global Warming Potential (GWP20) that is 84x that reported for CO2 in the latest IPCC report; therefore, the promise of natural gas as a clean fuel can only by realized if emissions of uncombusted gas are sufficiently low. To address this problem, there is a need for both regional (basin wide) measurements of methane emissions to determine global levels, as well as localized measurements to allow identification and reduction of emissions ("leaks") from specific equipment. The goal of this research is to develop a mobile open-path cavity ring-down spectroscopy (CRDS) sensor for localized measurements of atmospheric methane. While designed with the oil and gas industry in mind, the technology also has application to study emissions from agricultural operations and those from other sectors. This thesis presents development from proof-of-concept open-path sensor through two mobile iterations. CRDS can provide fast, non-intrusive, sensitive measurements; but in contrast to available instruments, the focus is on open-path operation (no flow-cell and pump) to provide opportunities for significant weight, size and power reductions to increase the mobility of the technique (<4 kg, <25 W). Challenges of open-path operation, such as fitting broadened spectral peaks, preserving mirror cleanliness and techniques for removing signal noise due to aerosol particles are addressed. The sensor is based on widely available and mature engineering near-infrared (NIR) opto-electronic components that have been developed for the telecom industry. Sensor validation with known methane concentrations show that the open-path sensor is capable of measuring atmospheric concentrations in the range of ~1.8-20+ ppmv at a rate of 1-3 Hz. Sensitivity studies using Allan variance techniques show sensitivity of < 20 ppbv in 1 – adequate for practical leak detection of small plumes <1 ppmv. Comparisons against a commercially available closed path sensor in mobile deployments are presented, along with mobile measurements from natural gas facilities in Platteville, CO and Washington County, PA. Finally, integration of the sensor onto a UAS platform for airborne measurements of methane and ammonia from agricultural applications is discussed.
Open Access
Examination of the potential impacts of dust and pollution aerosol acting as cloud nucleating aerosol on water resources in the Colorado River Basin
(Colorado State University. Libraries, 2016) Jha, Vandana, author; Cotton, William R., advisor; Rutledge, Steven A., committee member; Pierce, Jeffrey, committee member; Ramirez, Jorge, committee member
In this study we examine the cumulative effect of dust acting as cloud nucleating aerosol (cloud condensation nuclei (CCN), giant cloud condensation nuclei (GCCN), and ice nuclei (IN)) along with anthropogenic aerosol pollution acting primarily as CCN, over the entire Colorado Rocky Mountains from the months of October to April in the year 2004-2005; the snow year. This ~6.5 months analysis provides a range of snowfall totals and variability in dust and anthropogenic aerosol pollution. The specific objectives of this research is to quantify the impacts of both dust and pollution aerosols on wintertime precipitation in the Colorado Mountains using the Regional Atmospheric Modeling System (RAMS). In general, dust enhances precipitation primarily by acting as IN, while aerosol pollution reduces water resources in the CRB via the so-called “spill-over” effect, by enhancing cloud droplet concentrations and reducing riming rates. Dust is more episodic and aerosol pollution is more pervasive throughout the winter season. Combined response to dust and aerosol pollution is a net reduction of water resources in the CRB. The question is by how much are those water resources affected? Our best estimate is that total winter-season precipitation loss for for the CRB the 2004-2005 winter season due to the combined influence of aerosol pollution and dust is 5,380,00 acre-feet of water. Sensitivity studies for different cases have also been run for the specific cases in 2004-2005 winter season to analyze the impact of changing dust and aerosol ratios on precipitation in the Colorado River Basin. The dust is varied from 3 to 10 times in the experiments and the response is found to be non monotonic and depends on various environmental factors. The sensitivity studies show that adding dust in a wet system increases precipitation when IN affects are dominant. For a relatively dry system high concentrations of dust can result in over-seeding the clouds and reductions in precipitation. However, when adding dust to a system with warmer cloud bases, the response is non-monotonical, and when CCN affects are dominant, reductions in precipitation are found.
Open Access
Low-cost embedded systems for community-driven ambient air quality monitoring
(Colorado State University. Libraries, 2022) Wendt, Eric, author; Volckens, John, advisor; Pierce, Jeffrey, committee member; Jathar, Shantanu, committee member; Pasricha, Sudeep, committee member
Fine particulate matter (PM2.5) air pollution is a leading cause of death, disease and environmental degradation worldwide. Existing PM2.5 measurement infrastructure provides broad PM2.5 sampling coverage, but due to high costs (>10,000 USD), these instruments are rarely broadly distributed at community-level scales. Low-cost sensors can be more practically deployed in spatial and temporal configurations that can fill the gaps left by more expensive monitors. Crowdsourcing low-cost sensors is a promising deployment strategy in which sensors are operated by interested community members. Prior work has demonstrated the potential of crowdsourced networks, but low-cost sensor technology remains ripe for improvement. Here we describe a body of work aimed toward bolstering the future of community-driven air quality monitoring through technological innovation. We first detail the development of the Aerosol Mass and Optical Depth (AMODv2) sampler, a low-cost monitor capable of unsupervised measurement of PM2.5 mass concentration and Aerosol Optical Depth (AOD), a measure of light extinction in the full atmospheric column due to airborne particles. We highlight key design features of the AMODv2 and demonstrate that its measurements are accurate relative to standard reference monitors. Second we describe a national crowdsourced network of AMODv2s, in which we leveraged the measurement capabilities of the AMODv2 in a network of university students to analyze the relationship between PM2.5 and AOD in the presence of wildfire smoke in the United States. Finally, we propose a cloud screening algorithm for AOD measurements using all-sky images and deep transfer learning. We found that our algorithm correctly screens over 95% of all-sky images for cloud contamination from a custom all-sky image data set. Taken as a whole, our work supports community-driven air pollution monitoring by advancing the tools and strategies communities need to better understand the air they breathe.
Open Access
Measurement of low-altitude aerosol layers surrounding convective cold pool passage observed by uncrewed aircraft
(Colorado State University. Libraries, 2024) Heffernan, Brian, author; Kreidenweis, Sonia, advisor; Perkins, Russell, advisor; Pierce, Jeffrey, committee member; Jathar, Shantanu, committee member
Convectively generated cold pools can have myriad impacts on local aerosol concentrations. Passage of cold pools may loft dust, pollen or other aerosols from the surface, and precipitation and humidity changes accompanying cold pools also impact local aerosols in several ways. The vertical profile of aerosols can have important effects on meteorology, however, the effects of cold pools on the vertical distribution of aerosol are largely unstudied. During the BioAerosol and Convective Storms (BACS) field campaigns in the Colorado plains in spring of 2022 and 2023, Uncrewed Aircraft (UA) were utilized to observe the vertical profile of aerosol, and how this vertical profile may be affected by the passage of cold pools. UAs with mounted aerosol and meteorological instrument packages were deployed in a vertical column to profile different atmospheric variables. Flights were conducted before, during, and after the passage of cold pools, and UA data were contextualized using radiosonde measurements and surface-based aerosol and meteorological instruments. A discussion of the challenges of UA-mounted aerosol sampling is presented. Validation experiments were conducted to assess the reliability of UA-mounted Optical Particle Counters (OPCs), and analyzed to show that UA-mounted OPCs can provide reliable data under certain circumstances. Two primary issues are discussed in detail: sensor drift and suppressed OPC sampling flow. A calibration procedure was developed and utilized to address the issue of sensor drift, while suppressed OPC sample flow was addressed by removing all data below a determined critical threshold flow rate. These methodologies lead to the creation of a robust data product for the measurement of aerosol vertical profiles using UA-mounted OPCs. Using these OPC data, an analysis of the vertical profiles observed during the BACS campaign is provided, up to 350m above the surface. We find that a common feature of a post cold pool environment is a layer of enhanced submicron aerosol concentration measured 120m above the surface. This feature and its evolution are examined in detail for several case studies, and different possible explanations are presented. Potential causes of this observed feature include pollen-rupture, low temperature inversions trapping aerosol in a low stable layer of elevated aerosol concentration, and emission and/or deposition of aerosols, but these explanations each appear to be insufficient. This feature appears to be caused by the dynamics of the cold pool, which can entrain and redistribute airmasses from different levels of the atmosphere.
Open Access
Methods for particulate matter emissions reduction in wood burning cookstoves
(Colorado State University. Libraries, 2015) Dischino, Kevin, author; Marchese, Anthony, advisor; Pierce, Jeffrey, committee member; Volckens, John, committee member
About 3 billion people cook by burning biomass. Most use inefficient cooking technologies that lead to high levels of domestic air pollution. This results in tremendous damages to human and environmental health. For example, in 2012 the World Health Organization estimated that 4.3 million people died prematurely from illnesses attributable to inefficient household use of biomass fuels.
Open Access
Microphysical, dynamical, and lightning processes associated with anomalous charge structures in isolated convection
(Colorado State University. Libraries, 2017) Fuchs, Brody, author; Rutledge, Steven, advisor; Dolan, Brenda, committee member; van den Heever, Susan, committee member; Pierce, Jeffrey, committee member; Eykholt, Richard, committee member
Internal storm charge structures are linked to storm microphysics and dynamics. This study leverages available radar-based microphysical and dynamical information from recent field campaigns to investigate the processes that influence storm-scale charge structures. Nine normal polarity (mid-level negative charge) cases that occurred in northern Alabama, and six anomalous polarity (mid-level positive charge) cases that occurred in northeastern Colorado are studied in detail. The results suggest the presence of positively charged mid-level graupel in anomalous polarity storms, which is consistent with large amounts of supercooled liquid water (SCLW). Even though the normal polarity storms have more thermodynamic instability, the anomalous polarity storms have broader and stronger updrafts in addition to more robust mixed-phase microphysics. We expect the broader and stronger updrafts in anomalous Colorado storms are more resistant to dilution by entrainment. Using representative updraft speeds and warm cloud depths, the amount of time a parcel spends in the warm phase of a cloud was estimated for each storm observation. This metric is found to be the key discriminator between the two storm populations as the stronger updrafts and shallower warm cloud depths in Colorado lead to much shorter warm cloud residence time in those storms. We hypothesize this parameter strongly influences the amount of SCLW in the mid-levels because it impacts the loss of liquid water in the warm phase of the cloud via autoconversion and coalescence. Using a recently developed automated flash clustering algorithm on multiple years of ground-based lightning mapping array (LMA) data, approximately 63 million lightning flashes were identified and analyzed from Washington DC, northern Alabama, and northeast Colorado. While LMA-based average annual flash density values in Washington DC (~ 20 flashes km-2 yr-1) and Alabama (~ 35 flashes km-2 yr-1) are within 50% of corresponding satellite estimates, LMA-based estimates are approximately a factor of 3 larger (~ 50 flashes km-2 yr-1) than satellite estimates in northeast Colorado. By estimating the initiation and propagation of lightning channels with LMA data, we find that flashes were produced at lower altitudes in Colorado, compared to Alabama or Washington DC. This is a result of the storm charge structures in these regions as normal polarity storms (common in Alabama and Washington DC) produce systematically higher altitude flashes and anomalous storms (common in Colorado) produce systematically lower altitude flashes.
Open Access
Modeling the formation and composition of secondary organic aerosol from diesel exhaust using parameterized and semi-explicit chemistry and thermodynamic models
(Colorado State University. Libraries, 2017) Eluri, Sailaja, author; Jathar, Shantanu, advisor; Volckens, John, committee member; Pierce, Jeffrey, committee member; Farmer, Delphine, committee member
Laboratory-based studies have shown that diesel-powered sources emit volatile organic compounds that can be photo-oxidized in the atmosphere to form secondary organic aerosol (SOA); in some cases, this SOA can exceed direct emissions of particulate matter (PM); PM is a criteria pollutant that is known to have adverse effects on air quality, climate, and human health. However, there are open questions surrounding how these laboratory experiments can be extrapolated to the real atmosphere and how they will help identify the most important species in diesel exhaust that contribute to SOA formation. Jathar et al. (2017) recently performed experiments using an oxidation flow reactor (OFR) to measure the photochemical production of SOA from a diesel engine operated at two different engine loads (idle, load), two fuel types (diesel, biodiesel) and two aftertreatment configurations (with and without an oxidation catalyst and particle filter). In this work, we will use two different SOA models, namely the volatility basis set (VBS) model and the statistical oxidation model (SOM), to simulate the formation, evolution and composition of SOA from the experiments of Jathar et al. (2017). Leveraging recent laboratory-based parameterizations, both frameworks accounted for a semi-volatile and reactive POA, SOA production from semi-volatile, intermediate-volatility and volatile organic compounds (SVOC, IVOC and VOC), NOx-dependent multigenerational gas-phase chemistry, and kinetic gas/particle partitioning. Both frameworks demonstrated that for model predictions of SOA mass and elemental composition to agree with measurements across all engine load-fuel-aftertreatment combinations, it was necessary to (a) model the kinetically-limited gas/particle partitioning likely in OFRs and (b) account for SOA formation from IVOCs (IVOCs were found to account for more than four-fifths of the model-predicted SOA). Model predictions of the gas-phase organic compounds (resolved in carbon and oxygen space) from the SOM compared favorably to gas-phase measurements made using a Chemical Ionization Mass Spectrometer (CIMS) that, qualitatively, substantiated the semi-explicit chemistry captured by the SOM and the measurements made by the CIMS. Sensitivity simulations suggested that (a) IVOCs from diesel exhaust could be modeled using a single surrogate species with an SOA mass yield equivalent to a C15 or C17 linear alkane for use in large-scale models, (b) different diesel exhaust emissions profiles in the literature resulted in the same SOA production as long as IVOCs were included and (c) accounting for vapor wall loss parameterizations for the SOA precursors improved model performance. As OFRs are increasingly used to study SOA formation and evolution in laboratory and field environments, there is a need to develop models that can be used to interpret the OFR data. This work is one example of the model development and application relevant to the use of OFRs.
Open Access
Multi-day evolution of organic aerosol mass and composition from biomass burning emissions
(Colorado State University. Libraries, 2023) Dearden, Abraham C., author; Jathar, Shantanu, advisor; Bond, Tami, committee member; Pierce, Jeffrey, committee member
Biomass burning is an important source of primary and secondary organic aerosol (POA, SOA, and together, OA) to the atmosphere. The photochemical evolution of biomass burning OA, especially over long photochemical ages, is highly complex and there are large uncertainties in how this evolution is represented in models. Recently, we performed photooxidation experiments on biomass burning emissions using a small environmental chamber (~150 L) to study the OA evolution over multiple equivalent days of photochemical aging. In this work, we use a kinetic, process-level model (SOM-TOMAS; Statistical Oxidation Model-TwO Moment Aerosol Sectional) to simulate the photochemical evolution of OA in 18 chamber experiments performed on emissions from 10 different fuels. A base version of the model was able to simulate the time-dependent evolution of the OA mass concentration and its oxygen-to-carbon ratio (O:C) at short photochemical ages (0.5 to 1 equivalent days) but substantially underestimated the enhancement in both metrics at longer photochemical ages (>1 equivalent day). The OA after several days of equivalent photochemical aging was dominated by SOA (58%, on average) with the remainder being POA (42%, on average). Semi-volatile organic compounds, oxygenated aromatics, and heterocyclics accounted for the majority (86%, on average) of the SOA formed. Experimental artifacts (i.e., particle and vapor wall losses) were found to be much more important in influencing the OA evolution than other processes (i.e., dilution, heterogeneous chemistry, and oligomerization reactions). Adjustments to the kinetic model seemed to improve model performance only marginally indicating that the model was missing precursors, chemical pathways, or both, especially to explain the observed enhancement in OA mass and O:C over longer photochemical ages. While far from ideal, this work contributes to a process-level understanding of biomass burning OA that is relevant for its evolution at regional and global scales.
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 member
Exposure 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.
Open Access
Residential cookstove emissions: measurement and modeling from the lab and field
(Colorado State University. Libraries, 2018) Bilsback, Kelsey, author; Volckens, John, advisor; Barnes, Elizabeth, committee member; Jathar, Shantanu, committee member; Marchese, Anthony, committee member; Pierce, Jeffrey, committee member
Emissions from solid-fuel cookstoves, which result from poorly controlled combustion, have been linked to indoor and outdoor air pollution, climate forcing, and human disease. The adverse effects of cookstoves have motivated commitment of substantial time and resources towards development of "improved" cookstoves that operate more efficiently and reduce emissions of harmful air pollutants. However, once disseminated to cookstove users, improved cookstoves often do not ameliorate air quality to a level that substantially reduces health risks or negative environmental impacts. Several critical knowledge gaps related to the emissions and performance of "improved" cookstoves exist; attempting to address these gaps is the subject of this dissertation. Widely-used laboratory testing protocols overestimate the ability of improved stoves to lower emissions. In this work, we develop and validated a novel laboratory test protocol entitled the Firepower Sweep Test. We find that the Firepower Sweep Test reproduces the range of PM2.5 and CO emissions observed in the field, including high emissions events not typically observed under current laboratory protocols. We also find that firepower is modestly correlated with emissions, although this relationship depends on stove-fuel combination. Our results justify incorporating multiple-firepower testing into laboratory-based protocols, but demonstrate that firepower alone cannot explain the observed variability in cookstove emissions. Cookstoves emit many pollutants; however, most studies only measure fine particulate matter (PM2.5) and carbon monoxide (CO). In this work, we present an extensive inventory of air pollutants emitted from wood, charcoal, kerosene, and liquefied petroleum gas (LPG) cookstoves. One-hundred and twenty pollutants, including PM2.5, CO, organic matter, elemental carbon, inorganic ions, carbohydrates, ultrafine particles, volatile organic compounds, carbonyls, and polycyclic aromatic hydrocarbons, are included in this inventory. Our results demonstrate that, while most improved stoves tend to reduce PM2.5 and/or CO emissions, reductions PM2.5 and/or CO emissions do not always correspond to reductions of other harmful pollutants. These findings highlight the need to characterize the full emissions profile of "improved" cookstove designs before they are disseminated to users. Accurate emissions data are critical inputs for models that aim to quantify the impacts of cookstoves on climate and health. Currently, model inputs are primarily derived from laboratory experiments that do not represent in-home use. In this work, we present a relatively inexpensive technique that uses a temperature measurement made at the combustion chamber outlet to estimate firepower. These firepower estimations have the potential to provide valuable information about the range of firepowers over which cookstoves are operated at during real-world use. We also demonstrate that in-use firepower measurements from "improved" cookstoves can be combined with laboratory emissions data from the Firepower Sweep Test to estimate in-use emissions using linear regression models. We find that the model predictions are accurate enough to determine which International Standards Organization emissions tier a given "improved" stove is likely to fall under.
Open Access
Secondary organic aerosol formation from volatile chemical product emissions: parameters and contributions to anthropogenic aerosol
(Colorado State University. Libraries, 2023) Sasidharan, Sreejith, author; Jathar, Shantanu, advisor; Volckens, John, committee member; Pierce, Jeffrey, committee member
Volatile chemical products (VCP) are an increasingly important source of hydrocarbon and oxygenated volatile organic compound (OVOC) emissions to the atmosphere, and these emissions are likely to play an important role as anthropogenic precursors for secondary organic aerosol (SOA). While the SOA from VCP hydrocarbons is often accounted for in ambient air quality models, the formation, evolution, and properties of SOA from VCP OVOCs remains uncertain. We use environmental chamber data and a kinetic model to develop SOA parameters for ten OVOCs representing glycols, glycol ethers, esters, oxygenated aromatics, and amines. Model simulations suggest that the SOA mass yields for these OVOCs are on the same magnitude as widely studied SOA precursors (e.g., long-chain alkanes, monoterpenes, and single-ring aromatics) and these yields exhibit a linear correlation with the difference between the carbon and oxygen numbers of the precursor. When combined with emissions inventories for two megacities in the United States (US) and a US-wide inventory, we find that VCPs form 0.8-2.5× as much SOA, by mass, as mobile sources. Hydrocarbons (terpenes, branched and cyclic alkanes) and OVOCs (terpenoids, glycols, glycol ethers) make up 60-75% and 25-40% of the SOA arising from VCP use, respectively. This work contributes to the growing body of knowledge focused on studying VCP VOC contributions to urban air pollution.
Open Access
Spatiotemporal variability of peroxy acyl nitrates (PANs) over megacities from satellite observations
(Colorado State University. Libraries, 2023) Shogrin, Madison J., author; Fischer, Emily V., advisor; Payne, Vivienne H., committee member; Pierce, Jeffrey, committee member; Miller, Steven, committee member; Magzamen, Sheryl, committee member
Peroxy acyl nitrates (PANs) are photochemical pollutants with implications for health and atmospheric oxidation capacity. PANs are formed via the oxidation of non-methane volatile organic compounds (NMVOCs) in the presence of nitrogen oxide radicals (NOx = NO + NO2). PANs serve as reservoir species and sources for NOx in outflow regions of megacities, facilitating O3 production downwind. While urban environments are large sources of PANs, in-situ observations in urban areas are generally limited. Here we use satellite measurements of PANs from the Tropospheric Emission Spectrometer (TES) and the S-NPP Cross-Track Infrared Sounder (CrIS) to evaluate the spatiotemporal variability of PANs over and surrounding 9 megacities: Mexico City, Beijing, Los Angeles, Tokyo, São Paulo, Delhi, Mumbai, Lagos, and Karachi. We use monthly mean values of PANs to determine the seasonal cycle within the urban center of megacities. We find pronounced seasonal cycles of PANs in megacities and seasonal maxima in PANs correspond to seasonal peaks in local photochemical activity. Local fire activity can explain some of the observed interannual variability in PANs over and around megacities. We use S-NPP CrIS data to probe the spatial outflow pattern of PANs produced within urban Mexico City during the month with the largest mixing ratios of PANs (April). Peak outflow in April occurs to the northeast of the city and over the mountains south of the city. Outflow to the northwest appears infrequent. CrIS is used to further explore changes in PANs associated with substantial declines in megacity NOx in response to the COVID-19 pandemic. We only identify two cities over which PANs changed significantly in response to NOx perturbations: Beijing and Los Angeles. This work demonstrates that the space-based observations provided by CrIS and TES can increase understanding of the spatiotemporal variability and sensitivity to precursor emissions of PANs over and around global megacities.
Open Access
Understanding meteorological impacts on ambient PM2.5 concentrations using random forest models in Beijing
(Colorado State University. Libraries, 2022) Brehmer, Collin, author; Carter, Ellison, advisor; Bond, Tami, committee member; Carlson, Kenneth, committee member; Pierce, Jeffrey, committee member
Policymakers and non-governmental organizations have been implementing policies and interventions designed to reduce exposure to hazardous air pollution. Having knowledge of how non-policy related factors (i.e., meteorology) impact air pollution concentrations in a given study area can better inform longitudinal studies of the effects of the policy on air pollution and health. In this study, we apply a random forest machine learning approach to evaluate how meteorological factors including temperature, relative humidity, wind speed, wind direction, and boundary layer height influence daily PM2.5 concentrations in rural Beijing villages during heating months (January and February of 2019 and 2020). Ten-fold cross validation indicated good model performance with an overall r2 of 0.85 for season 1, and 0.93 for season 2. The models were able to identify variables that were the most important for predicting PM2.5 concentrations both field seasons (relative humidity) and variables that had changes in relative importance between seasons (temperature and boundary layer height). Additionally, examination of one and two-way partial dependence plots as well as interactions through Friedman's H-statistic granted insight into how meteorology variables influence PM2.5 concentrations. Findings from this work provide a basis for adjusting for meteorological variability in important indicators of air quality like PM2.5 concentrations in an ongoing real-world policy evaluation of a province-wide ban on household use of coal for space heating in Beijing, which is critical for isolating (to the extent possible) changes in measured pollutant concentrations attributable to the policy.
Open Access
Using operational HMS smoke observations to gain insights on North American smoke transport and implications for air quality
(Colorado State University. Libraries, 2016) Brey, Steven J., author; Fischer, Emily V., advisor; Barnes, Elizabeth, committee member; Pierce, Jeffrey, committee member; Rocca, Monique, committee member
Wildfires represent a major challenge for air quality managers, as they are large sources of particulate matter (PM) and ozone (O3) precursors, and they are highly dynamic and transient events. Smoke can be transported thousands of kilometers to deteriorate air quality over large regions. Under a warming climate, fire severity and frequency are likely to in- crease, exacerbating an existing problem. Using the National Environmental Satellite, Data and Information Service (NESDIS) Hazard Mapping System (HMS) smoke data for the U.S. and Canada for the period 2007 to 2014, I examine a subset of fires that are confirmed to have produced sufficient smoke to warrant the initiation of a National Weather Service smoke forecast. The locations of these fires combined with Hybrid Single Particle Lagragian Integrated Trajectory Model (HYSPLIT) forward trajectories, satellite detected smoke plume data, and detailed land-cover data are used to develop a climatology of the land- cover, location, and seasonality of the smoke that impacts the atmospheric column above 10 U.S. regions. I examine the relative contribution of local versus long-range transport to the presence of smoke in different regions as well as the prevalence of smoke generated by agricultural burning versus wildfires. This work also investigates the influence of smoke on O3 abundances over the contiguous U.S. Using co-located observations of particulate matter and the NESDIS HMS smoke data, I identify summertime days between 2005 and 2014 that Environmental Protection Agency Air Quality System O3 monitors are influenced by smoke. I compare O3 mixing ratio distributions for smoke-free and smoke-impacted days for each monitor, while accounting for temperature. This analysis shows that (i) the mean O3 abundance measured on smoke-impacted days is higher than on smoke-free days at 20% of monitoring locations, and (ii) the magnitude of the difference between smoke-impacted and smoke-free mixing ratios varies by location and is sensitive to the minimum temperature allowed for smoke-free days. For each site, I present the percentage of days when the 8-hr average O3 mixing ratio (MDA8) exceeds 75 ppbv and smoke is present. When our most lenient temperature criteria are applied to smoke-free days, smoke-impacted O3 mixing ratios are most elevated in locations with the highest emissions of nitrogen oxides. The Northeast corridor, Dallas, Houston, Atlanta, Birmingham, and Kansas City stand out as having smoke present 10-20% of the days when 8-hr MDA8 O3 mixing ratios exceed 75 ppbv. Most U.S. cities maintain a similar proportion of smoke-impacted exceedance days when they are held against the new MDA8 limit of 70 ppbv.