Lifetime and distribution of ozone and related pollutants in the eastern United States

Most major cities in the eastern United States have air quality deemed unhealthy by the EPA under a set of regulations known as the National Ambient Air Quality Standards (NAAQS). The worst air quality in Maryland is measured in Edgewood, MD, a small community located along the Chesapeake Bay and generally downwind of Baltimore during hot, summertime days. Direct measurements and numerical simulations were used to investigate how meteorology and chemistry conspire to create adverse levels of photochemical smog especially at this coastal location. Ozone (O3) and oxidized reactive nitrogen (NOy), a family of ozone precursors, were measured over the Chesapeake Bay during a ten day experiment in July 2011 to better understand the formation of ozone over the Bay and its impact on coastal communities such as Edgewood. Ozone over the Bay during the afternoon was 10% to 20% higher than the closest upwind ground sites. A combination of complex boundary layer dynamics, deposition rates, and unaccounted marine emissions play an integral role in the regional maximum of ozone over the Bay. The CAMx regional air quality model was assessed and enhanced through comparison with data from NASA’s 2011 DISCOVER-AQ field campaign. Comparisons show a model overestimate of NOy by +86.2% and a model underestimate of formaldehyde (HCHO) by –28.3%. I present a revised model framework that better captures these observations and the response of ozone to reductions of precursor emissions. Incremental controls on electricity generating stations will produce greater benefits for surface ozone while additional controls on mobile sources may yield less benefit because cars emit less pollution than expected. Model results also indicate that as ozone concentrations improve with decreasing anthropogenic emissions, the photochemical lifetime of tropospheric ozone increases. The lifetime of ozone lengthens because the two primary gas-phase sinks for odd oxygen (Ox ≈ NO2 + O3) – attack by hydroperoxyl radicals (HO2) on ozone and formation of nitrate – weaken with decreasing pollutant emissions. This unintended consequence of air quality regulation causes pollutants to persist longer in the atmosphere, and indicates that pollutant transport between states and countries will likely play a greater role in the future.

OBSERVATIONS AND EMISSIONS OF ENERGY-ASSOCIATED OZONE PRECURSORS IN THE MID-ATLANTIC UNITED STATES

Surface ozone is formed in the presence of NOx (NO + NO2) and volatile organic compounds (VOCs) and is hazardous to human health. A better understanding of these precursors is needed for developing effective policies to improve air quality. To evaluate the year-to-year changes in source contributions to total VOCs, Positive Matrix Factorization (PMF) was used to perform source apportionment using available hourly observations from June through August at a Photochemical Assessment Monitoring Station (PAMS) in Essex, MD for each year from 2007-2015. Results suggest that while gasoline and vehicle exhaust emissions have fallen, the contribution of natural gas sources to total VOCs has risen. To investigate this increasing natural gas influence, ethane measurements from PAMS sites in Essex, MD and Washington, D.C. were examined. Following a period of decline, daytime ethane concentrations have increased significantly after 2009. This trend appears to be linked with the rapid shale gas production in upwind, neighboring states, especially Pennsylvania and West Virginia. Back-trajectory analyses similarly show that ethane concentrations at these monitors were significantly greater if air parcels had passed through counties containing a high density of unconventional natural gas wells. In addition to VOC emissions, the compressors and engines involved with hydraulic fracturing operations also emit NOx and particulate matter (PM). The Community Multi-scale Air Quality (CMAQ) Model was used to simulate air quality for the Eastern U.S. in 2020, including emissions from shale gas operations in the Appalachian Basin. Predicted concentrations of ozone and PM show the largest decreases when these natural gas resources are hypothetically used to convert coal-fired power plants, despite the increased emissions from hydraulic fracturing operations expanded into all possible shale regions in the Appalachian Basin. While not as clean as burning natural gas, emissions of NOx from coal-fired power plants can be reduced by utilizing post-combustion controls. However, even though capital investment has already been made, these controls are not always operated at optimal rates. CMAQ simulations for the Eastern U.S. in 2018 show ozone concentrations decrease by ~5 ppb when controls on coal-fired power plants limit NOx emissions to historically best rates.

Selected Solo Music for Saxophone by United States Composers: 1975-2005

This dissertation project identifies important works for solo saxophone by United States composers between 1975 and 2005. The quality, variety, expressiveness, and difficulty of the solo saxophone repertoire during these thirty years is remarkable and remedies, to some extent, the fact that the saxophone had been a largely neglected instrument in the realm of classical music. In twentieth-century music, including Jazz, the saxophone developed, nevertheless, a unique and significant voice as is evident in the saxophone repertoire that expands immensely in many instrumental settings, including the orchestra, solo works, and a wide variety of chamber ensembles. Historically, the saxophone in the United States first found its niche in Vaudeville, military bands, and jazz ensembles, while in Europe composers such as Debussy, D'Indy, Schmitt, Ibert, Glazounov, Heiden, and Desenclos recognized the potential of the instrument and wrote for it. The saxophone is well suited to the intimacy and unique timbral explorations of the solo literature, but only by the middle twentieth century did the repertoire allow the instrument to flourish into a virtuosic and expressive voice presented by successive generations of performers – Marcel Mule, Sigurd Rascher, Cecil Leeson, Jean-Marie Londeix, Fred Hemke, Eugene Rousseau, and Donald Sinta. The very high artistic level of theses soloists was inspiring and dozens of new compositions were commissioned. Through the 1960’s American composers such as Paul Creston, Leslie Bassett, Henry Cowell, Alec Wilder, and others produced eminent works for the saxophone, to be followed by an enormous output of quality compositions between 1975 and 2005. The works chosen for performance were selected from thousands of compositions between 1975 and 2005 researched for this project. The three recital dates were: April 6, 2005, in Gildenhorn Recital Hall, December 4, 2005, in Ulrich Recital Hall, and April 15, 2006, in Gildenhorn Recital Hall. Recordings of these recitals may be obtained in person or online from the Michelle Smith Performing Arts Library of the University of Maryland, College Park.