Atmospheric & Oceanic Science Theses and Dissertations
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Item REMOTE SENSING OF ATMOSPHERIC TRACE GASES FROM SPACEBORNE UV MEASUREMENTS(2022) Huang, Xinzhou; Yang, Kai; Dickerson, Russell R.; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Satellite measurements of atmospheric trace gases provide continuous long-term information for monitoring the atmospheric chemical environment and air quality at local, regional, and global scales. Trace gas retrievals play a critical role in chemical data assimilation, air quality modeling and forecast, and regulatory decision-making. In this dissertation, I present retrievals of three trace gases species (O3, SO2, and NO2) from measurements of Ultraviolet (UV) radiation made from the imaging spectrometers onboard operational satellites, including the Earth Polychromatic Imaging Camera (EPIC) onboard the Deep Space Climate Observatory (DSCOVR), the Ozone Mapping and Profiler Suite - Nadir Mapper (OMPS-NM) onboard Suomi-NPP (SNPP), and the OMPS-NM onboard NOAA-20 satellite. The retrievals of the trace gas vertical columns are achieved through the Direct Vertical Column Fitting (DVCF) algorithm, which is designed to maximize the absorption signature from the Earth’s atmosphere in the UV spectral range. This dissertation first demonstrates the theoretical basis and mathematical procedures of the DVCF algorithm used for retrieving total vertical columns of ozone (O3) and sulfur dioxide (SO2) from DSCOVR EPIC. We describe algorithm advances, including an improved O3 profile representation that enables profile adjustments from multiple spectral measurements and the spatial optimal estimation (SOE) scheme that reduces O3 artifacts resulted from EPIC’s band-to-band misregistrations. Furthermore, we present detailed error analyses to quantify retrieval uncertainties from various sources, assess EPIC-observed volcanic plumes, and validate O3 and SO2 retrievals with correlative data. The second part of this dissertation presents a suite of efforts to retrieve the tropospheric and stratospheric NO2 vertical columns from the new NOAA-20 OMPS hyperspectral Ultraviolet-Visible (UV-Vis) instrument, covering retrieval algorithm, Stratosphere-Troposphere Separation (STS) scheme, measurement sensitivity assessment, inter-comparison with the Ozone Monitoring Instrument (OMI), evaluation with ground-based Pandora spectrometers, as well as a case study of drastic NO2 changes during COVID-19 pandemic. The third part of my dissertation focuses on validation and algorithm improvements for the tropospheric NO2 retrievals from SNPP OMPS UV measurements. OMPS column NO2 was validated against coincidence measurements from two ground-based MAX-DOAS spectrometers deployed in eastern China. To achieve higher retrieval accuracy, we developed and implemented a series of algorithm improvements, including an explicit aerosol correction scheme to account for changes in measurement sensitivity caused by aerosol scattering and absorption, the replacement of climatological a priori NO2 profile with more accurate NO2 vertical distribution from high-resolution CMAQ model simulations, and the application of model-derived spatial weighting kernel to account for the effect of heterogeneous subpixel distribution. These improvements yield more accurate OMPS NO2 retrievals in better agreement with MAX-DOAS NO2 measurements. The analysis concluded that explicit aerosol correction and a priori profile adjustment are critical for improving satellite NO2 observations in highly polluted regions and spatial downscaling is helpful in resolving NO2 subpixel variations.Item APPLICATIONS OF THE OZONE MONITORING INSTRUMENT IN OBSERVING VOLCANIC SULFUR DIOXIDE PLUMES AND SULFATE DEPOSITION(2021) Fedkin, Niko Markovich; Dickerson, Russell R; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sulfur dioxide (SO2), a gas emitted by both volcanoes and anthropogenic activity, is a major pollutant and a precursor to sulfate aerosols. Sulfates can be deposited back to the ground where they have adverse impact on the environment or reside in the stratosphere as aerosols and affect radiative forcing. I investigated two components that stem from SO2: the deposition of sulfate, and the remote sensing of the SO2 layer height, important for aviation safety and chemical modeling. In the first study, I used column SO2 data from the Ozone Monitoring Instrument (OMI), and sulfate wet deposition data from the National Atmospheric Deposition Program to investigate the temporal and spatial relationship between trends in SO2 emissions and the downward sulfate wet deposition over the northeastern U.S. from 2005 to 2015. The results showed that emission reductions are reflected in deposition reductions within this same region. Emission reductions along the Ohio River Valley led to decreases in sulfate deposition not only in eastern OH and western PA, but also further downwind at sites in Delaware and Maryland. The findings suggested that emissions and wet deposition are linked through not only the location of sources relative to the observing sites, but also photochemistry and weather patterns characteristic to the region in winter and summer. The second part of this dissertation focuses on SO2 layer height retrievals and their applications. To this end I applied the Full Physics Inverse Learning Machine (FP-ILM) algorithm to OMI radiances in the spectral range of 310-330 nm. This approach utilized radiative transfer calculations to generate a large dataset of synthetic radiance spectra for a wide range of geophysical parameters. The spectral information was then used to train a neural network to predict the SO2 height. The main advantage of the algorithm is its speed, retrieving plume height in less than 10 min for an entire OMI orbit. I also compared the SO2 height retrievals to other data sources and explored some potential applications, in particular their use in volcanic SO2 plume forecasts and estimating the total mass emitted from volcanic eruptions.Item EXAMINATION OF TROPOSPHERIC OZONE AND ITS PRECURSORS WITHIN AN AIR QUALITY MODEL AND IMPLICATIONS FOR AIR QUALITY AND CLIMATE(2021) Hembeck, Linda; Salawitch, Ross J; Canty, Timothy P; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Elevated levels of tropospheric ozone (O3) caused by emissions of NOx and VOCs negatively impact human health, crops, and ecosystems. Even if precursor emissions are reduced below current levels, predicted higher temperatures due to increased greenhouse gas emissions could impede resulting air quality benefits. Air quality models simulate the complex relationships that form O3 and are used to guide policy decisions directed at improving O3. The body of this work encompasses three projects related to improvements in the representation of O3 and precursors in air quality models. First, I examine the role of O3 and its precursors in air quality and climate change by evaluating ozone production efficiency (OPE) and O3 precursors within models. I modified a chemical mechanism and the emissions of NOx to accurately represent NOx, the reactivity of NOx with peroxy radicals, HCHO, isoprene, as well as organic and inorganic NOy reservoir species. Implementation of these modifications increased confidence in model simulations. Results indicate accepted inventories overestimated NOx emissions but underestimate total VOC reactivity and OPE. Second, I examined the dependence of surface O3 on temperature (climate penalty factor (CPF)) throughout a period of 11 years within an air quality model and measurements. Future increases in temperature could offset benefits from future reductions in the emission of O3 precursors. Determining and understanding the CPF is critical to formulating effective strategies to reduce future exceedances. I have demonstrated that the model can reproduce O3 sensitivity to temperature reasonably well. By controlling emissions specifically of NOx mankind has reduced its vulnerability. Third, I compare satellite-observed and modeled ammonia (NH3) under varying chemical environments over East Asia. Regulation of O3 precursor concentrations in the atmosphere has an indirect effect on NH3 concentrations. Air quality policy to reduce NOx and through that also nitric acid (HNO3) in the atmosphere can result in an increase in the concentration of NH3 because of its neutralizing ability. Therefore, a less acidic atmosphere sequesters less NH3. This preliminary work exposes different areas that need to be addressed to gain greater insight into NH3 emissions and chemistry.Item REMOTE SENSING OF AEROSOL AND THE PLANETARY BOUNDARY LAYER, AND EXPLORING THEIR INTERACTIONS(2022) SU, Tianning; Li, Zhanqing; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosol-planetary boundary layer (PBL) interaction (API) is an important mechanism affecting the thermodynamics and convection in the lower atmosphere. API plays a critical role in the formation of severe pollution events and the development of convective clouds. Despite the progress made in understanding these processes, their magnitude and significance still have large uncertainties, varying significantly with aerosol distribution, aerosol optical property, and meteorological conditions. This study attempts to develop advanced remote sensing algorithms to retrieve information about the PBL and the aerosols contained within it. These remote sensing techniques are further used to elucidate the mechanisms governing API, enhancing our ability to predict air quality and model convective clouds, as well as understand the impact of aerosols on the climate system.In particular, we develop algorithms to improve the retrieval accuracy of aerosols and the PBL from satellite sensors and a ground-based lidar. For aerosol remote sensing, we use the deep neural network (DNN) to construct surface reflectance relationships (SRR) between different wavelengths. We then incorporate the DNN-constrained SRR into a traditional dark-target algorithm to retrieve the aerosol optical depth (AOD) using information from a current-generation geostationary satellite, i.e., Himawari-8, as input. As a result, the performance of AOD retrievals over East Asia is significantly improved. For PBL remote sensing, we explore different techniques for retrieving the PBL height (PBLH) from both a space-borne lidar (i.e., the Cloud-Aerosol Lidar with Orthogonal Polarization) and a ground-based lidar. We further develop a new method that combines lidar-measured aerosol backscatter with a stability-dependent model of PBLH diurnal variation. The new method circumvents or alleviates an inherent limitation of lidar-based PBLH detection when a residual layer of aerosols does not change in phase with the evolving thermodynamics. By separately considering surface-cloud coupling regimes, this method also offers high-quality retrievals of PBLH under cloudy conditions. Utilizing the enhanced retrievals of PBLH and synergistic measurements, we can also address some scientific questions concerning API, including the influencing factors of API and the role of aerosol vertical distributions. The correlation between the PBLH and the concentration of particulate matter with aerodynamic diameters less than 2.5 microns is generally negative. However, the magnitude, significance, and even the sign of their relationship vary greatly, depending on location and meteorological and aerosol conditions. In particular, API is considerably different under three aerosol vertical structure scenarios (i.e., well-mixed, decreasing and increasing with height). The vertical distribution of aerosol radiative forcing differs dramatically among the three types, with strong heating in the lower, middle, and upper PBL, respectively. Such a discrepancy in aerosol radiative forcing leads to different aerosol effects on atmospheric stability and entrainment processes. Absorbing aerosols are much less effective in stabilizing the lower atmosphere when aerosols decrease with height than in an inverted structure scenario.Item EXAMINATION OF PHOTOCHEMISTRY AND METEOROLOGY OF ATMOSPHERIC POLLUTANTS FROM THE NORTH CHINA PLAIN(2020) Benish, Sarah Elizabeth; Dickerson, Russell R; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increasingly severe air pollution over metropolitan regions in China has raised attention in light of its local and regional impacts on health and climate. Computer models can simulate complex interactions between photochemistry and meteorology to inform policy decisions in reducing ground-level pollution. However, models rely on an accurate portrayal of emissions that often possess large uncertainties over regions with evolving pollution characteristics. This work is comprised of a quantitative analysis of air pollutants in the North China Plain that strives to improve such uncertainties by identification of important sources and meteorological conditions for pollution through the combination of observations and models. Measurements used in this dissertation focus on in situ observations from the Spring 2016 Air chemistry Research in Asia (ARIAs) campaign, which sampled atmospheric composition across the heavily populated and industrialized Hebei Province in the North China Plain. High amounts of ozone (O3) precursors were found throughout and even above the planetary boundary layer, continuing to generate O3 at high rates to be potentially transported downwind. Evidence for the importance of anthropogenic VOCs on O3 production is presented. Concentrations of NOx and VOCs even in the rural areas of this highly industrialized province promote widespread O3 production and in order to improve air quality over Hebei, both NOx and VOCs should be regulated. The ARIAs airborne measurements also provide a critical opportunity to characterize chlorofluorocarbons (CFCs) over a suspected CFC-11 source region in China, finding mixing ratios were well above 2016 global background levels. Based on correlations of CFCs with compounds used in their manufacture, I identify likely source regions of new CFCs production and release, in violation of the Montreal Protocol. Finally, I examine the influence of meteorology on surface and aloft measurements during ARIAs. A multiday persistent high pressure episode is presented as a case study to examine the influence of regional transport on air quality measured during ARIAs. This dissertation provides valuable information for understanding one of the most polluted regions in China. Coordinated field and modeling efforts can together provide scientific guidance to inform pollution control measures to meet air quality targets in China.Item Exploring Regional Emissions and Tropospheric Ozone in the Eastern United States Using Air Quality Models and Data Products(2019) Ring, Allison Marie; Canty, Timothy P; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tropospheric ozone (O3) is a harmful pollutant regulated by the US Environmental Protection Agency (EPA) through the use of designated air quality standards. Within the United States, approximately 110 million people live within counties designated as in non-attainment of the O3 standard. In this work, analysis is performed to examine the influence of anthropogenic emissions on tropospheric O3 production within the framework of the CMAQ regulatory air quality model. Adjustments are recommended to improve emission representation from the largest (class 3) commercial marine vessels (c3 Marine). Model results with the implemented corrections show improved comparison to surface O3 observations from AQS sites. Characterization of the photochemical O3 production regime (VOC or NOx sensitive) is performed using the ratio of formaldehyde (HCHO) and nitrogen dioxide (NO2) tropospheric column observations from the satellite borne Ozone Monitoring Instrument (OMI), and whole air sampling canisters in the Long Island Sound (LIS) collected on May 17th and 18th, 2017. Evidence for the importance of anthropogenic VOCs in the New York City pollution plume and their role in tropospheric O3 production is presented. Aircraft O3 observations are used to evaluate model performance of the National Oceanic Atmospheric Administration (NOAA) National Air Quality Forecast Capability system CMAQ model for the O3 event in the LIS. Finally, a series of CMAQ simulations are performed to suggest the likely inventory sector (non-road mobile) most responsible for the significant O3 production downwind of coastal urban centers like New York and Chicago. Important air quality policy implications of these findings are discussed.Item Estimates of Regional Carbon Dioxide Fluxes Using a Dense Network of Low-Cost In Situ Observations(2018) Martin, Cory; Zeng, Ning; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Current inverse modeling-based estimates of carbon dioxide (CO2) fluxes in urban areas typically use a network of 10-20 observation sites featuring high-accuracy gas analyzers that can cost over $100,000 each. Recently, commercially available, low-cost sensors to measure both traditional meteorological quantities and trace gases such as CO2 have become a focus of atmospheric science research. These flux estimations are an ill-posed problem in the sense that, depending on resolution, the mathematical model may be optimizing fluxes for hundreds or even thousands of grid points, with only relatively few observations to use as constraint. Theoretically, by introducing many more observations into the system, the result will better represent the true state of the surface fluxes. This work comprises of three related studies that evaluate the viability of using a low-cost CO2 sensor combined with a mesoscale meteorology model with online tracers, and an advanced ensemble data assimilation technique, to estimate surface fluxes of CO2 in an urban region. First, the SenseAir K30 sensor is evaluated compared to a reference gas analyzer to determine the accuracy and precision of the observations from this sensor. Next, a simulation of atmospheric CO2 is evaluated against observations to understand the error in simulated mole fractions from variations in existing emissions inventories. Finally, a series of observing system simulation experiments (OSSEs) are conducted to understand the sensitivity of estimated CO2 fluxes to the ensemble data assimilation system configuration. From this work, it is found that the K30 sensor can be useful for urban ambient monitoring of CO2 after corrections for environmental factors such as temperature and pressure. Additionally, the modeled CO2 results show that the error in simulated mole fractions is likely larger from meteorological error than it is from uncertainty in emissions. Finally, the OSSEs find that this ensemble data assimilation system using a dense network of lower-accuracy observations can achieve comparable CO2 flux estimation results to that of using a sparse network of high-accuracy observations. However, the configuration of the system, particularly the inflation technique used, can significantly affect the quality of the analyzed fluxes.Item DEEP CONVECTIVE TRANSPORT AND WET SCAVENGING IN DIFFERENT CONVECTIVE REGIMES DURING THE DC3 FIELD CAMPAIGN(2018) Li, Yunyao; Pickering, Kenneth; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Deep convective transport of surface moisture and pollution from the planetary boundary layer to the upper troposphere and lower stratosphere affects the radiation budget and climate. Firstly, I analyzed the deep convective transport through cloud-resolved simulations of three different convective regimes from the 2012 Deep Convective Clouds and Chemistry (DC3) field campaign: an airmass thunderstorm, a supercell storm, and a mesoscale convective system (MCS). Analysis of vertical flux divergence shows that deep convective transport in the supercell case is the strongest per unit area, while transport of boundary layer insoluble trace gases is relatively weak in the MCS due to the injection of clean air into the mid-troposphere by a strong rear inflow jet. Additionally, forward and backward trajectories are used to determine the source of the upper-level detrained air. My second focus is using of cloud parameterized Weather Research and Forecasting model coupled with chemistry (WRF-Chem) simulations to analyze the subgrid deep convective transport in the supercell case and MCS case. Based on the precipitation results, the best WRF simulation of these storms was obtained with use of the Grell-Freitas (GF) convective scheme. The default subgrid convective transport scheme was replaced with a scheme to compute convective transport within the GF subgrid cumulus parameterization, which resulted in improved transport simulations. The results demonstrate the importance of having subgrid convective transport consistent with the convective parameterization in regional models. Moreover, the subgrid scale convective transport played a more significant role in the supercell case than the MCS case. I evaluated the model-simulated subgrid wet scavenging of soluble trace gases (such as HNO3, CH2O, CH3OOH, H2O2, and SO2) in the supercell case, and improved subgrid wet scavenging by determining appropriate ice retention factors, and by adjusting the conversion rate of cloud water to rain water. The introduction of the ice retention factors greatly improved the model simulation of less soluble species (e.g. decreased the CH2O simulation error by 12 % and decreased the CH3OOH simulation error by 63%). Finally, I conducted a > 24-hour long simulation to examine downwind ozone production and its sensitivity to the ice retention factors.Item EXAMINATION OF THE PHOTOCHEMISTRY AND MESOSCALE METEOROLOGY ASSOCIATED WITH POOR AIR QUALITY IN THE U.S.(2018) Mazzuca, Gina; Dickerson, Russell R; Pickering, Kenneth E; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mesoscale meteorological processes including advection, vertical mixing, thermally-direct circulations (sea/bay breezes) combined with chemical processes and deposition dominate boundary-layer ozone (O3). While bay breezes (BBs) transport higher O3 over land on polluted days, they also advect humid air and induce low-level convergence, which can lead to haze and deep convection. Thunderstorms can vent pollution out of the boundary layer and entrain cleaner, mid-tropospheric air into it, reducing surface pollutant concentrations. Here, the net local effect of these two mesoscale forcings (BBs and thunderstorms) on O3 concentrations are quantified. First, case studies using vertical profiles and surface observations during the 2011 MD and the 2013 TX deployments of DISCOVER-AQ show the severity of bay/gulf breeze exacerbation of pollution. Next is a BB and thunderstorm climatology for a Chesapeake Bay coastal site (summer 2011-2016). BBs are identified by a data-driven automated detection algorithm customized for the complex coastline. Thunderstorm vs. non-thunderstorm days are analyzed using gridded lightning data within an influential radius of the site. These meteorological classifications are compared with O3 exceedance days. While the highest conditional mean O3 was on BB days and the lowest on thunderstorm only days, thunderstorms do not always terminate an O3 event, especially in combination with a BB. To further understand the dynamical mechanisms responsible for changes in O3 from BBs and thunderstorms, the Weather Research and Forecasting (WRF) model is run at fine resolution with water vapor nudging to capture air-mass thunderstorms forced by the BB in MD. The model compared well with DISCOVER-AQ observations and radar reflectivity. Finally, an observation-constrained box model was used to study photochemical processes along the flight track during the 2013 TX DISCOVER-AQ deployment. O3 production and its sensitivity to NOx and VOCs were calculated at different locations and times of day. Results indicate controlling NOx emissions will benefit the Houston area overall, but select areas will also benefit from controlling VOC emissions. These studies, which can also be applied to particulate matter, uncover how meteorology and photochemistry come together to generate smog events at coastal cities, and can help develop efficient, high resolution policies for cleaner air.Item An Investigation of the Parameterized Prediction of Lightning in Cloud-Resolved Convection and the Resulting Chemistry(2017) Smith, Kristin; Pickering, Kenneth E; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Deep Convective Clouds and Chemistry (DC3) field campaign provided a unique set of observations to further investigate the role lightning and lightning-generated nitrogen oxides (LNOx) have on the composition of the upper troposphere. With the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), a cloud-resolved simulation of the 29-30 May 2012 severe supercell system investigated 18 flash rate parameterization schemes (FRPSs), the mean LNOx production per flash, and the transport and distribution of other trace gases. Most of the observed storm’s meteorological and chemical conditions were well represented when the model included convective damping and lightning data assimilation techniques. Newly-developed FRPSs based on DC3 radar observations and Lightning Mapping Array (LMA) data are implemented in the model, along with previously developed schemes from the literature. The schemes are based on relationships between lightning and various kinematic, structural, and microphysical thunderstorm characteristics available in the model. The results suggest the simulated graupel and snow/ice hydrometeors require scaling factors to more closely represent proxy observations. The model flash rates generated over the simulation period are compared with LMA observations. Thirteen FRPSs overpredicted flashes by > 100%. Generally, FRPSs based on storm kinematics and structure (particularly updraft volume) perform slightly better than schemes based on hydrometeors. However, the upward cloud ice flux FRPS best represents the observed lightning. The 10 WRF-Chem simulations included one run with no LNOx and nine runs with different LNOx production scenarios. The simulated CO and O3 are within 1% and 3% of aircraft observations, respectively, when compared with one model layer lower, which suggests the model slightly underestimates the convective transport. A LNOx production scenario of 82 moles per flash best represents the observed NOx mixing ratios in anvil outflow when combined with the observed flash channel vertical profiles and intracloud to cloud-to-ground ratios. This estimate is smaller than the mean 250 moles NO per flash suggested for a typical thunderstorm, but within the lower end of the estimated range (33-660 moles per flash). Analysis of the convective outflow using observations made 12-24 hours downwind indicates the mean daytime photochemical O3 production rate is about 1.6 ppbv per hour.