Atmospheric & Oceanic Science
Permanent URI for this communityhttp://hdl.handle.net/1903/2264
Formerly known as the Department of Meteorology.
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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 RELATIONSHIP BETWEEN COLUMN DENSITY AND SURFACE MIXING RATIO FOR O3 AND NO2: IMPLICATIONS FOR SATELLITE OBSERVATIONS AND THE IMPACTS OF VERTICAL MIXING(2016) Flynn, Clare Marie; Pickering, Kenneth E; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Satellites have great potential for diagnosis of surface air quality conditions, though reduced sensitivity of satellite instrumentation to the lower troposphere currently impedes their applicability. One objective of the NASA DISCOVER-AQ project is to provide information relevant to improving our ability to relate satellite-observed columns to surface conditions for key trace gases and aerosols. In support of DISCOVER-AQ, this dissertation investigates the degree of correlation between O3 and NO2 column abundance and surface mixing ratio during the four DISCOVER-AQ deployments; characterize the variability of the aircraft in situ and model-simulated O3 and NO2 profiles; and use the WRF-Chem model to further investigate the role of boundary layer mixing in the column-surface connection for the Maryland 2011 deployment, and determine which of the available boundary layer schemes best captures the observations. Simple linear regression analyses suggest that O3 partial column observations from future satellite instruments with sufficient sensitivity to the lower troposphere may be most meaningful for surface air quality under the conditions associated with the Maryland 2011 campaign, which included generally deep, convective boundary layers, the least wind shear of all four deployments, and few geographical influences on local meteorology, with exception of bay breezes. Hierarchical clustering analysis of the in situ O3 and NO2 profiles indicate that the degree of vertical mixing (defined by temperature lapse rate) associated with each cluster exerted an important influence on the shapes of the median cluster profiles for O3, as well as impacted the column vs. surface correlations for many clusters for both O3 and NO2. However, comparisons to the CMAQ model suggest that, among other errors, vertical mixing is overestimated, causing too great a column-surface connection within the model. Finally, the WRF-Chem model, a meteorology model with coupled chemistry, is used to further investigate the impact of vertical mixing on the O3 and NO2 column-surface connection, for an ozone pollution event that occurred on July 26-29, 2011. Five PBL schemes were tested, with no one scheme producing a clear, consistent “best” comparison with the observations for PBLH and pollutant profiles; however, despite improvements, the ACM2 scheme continues to overestimate vertical mixing.Item Air Pollutant Concentrations and Trends over the Eastern U.S. and China: Aircraft Measurements and Numerical Simulations(2012) He, Hao; Dickerson, Russell R.; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In the last several decades, efforts have been made to mitigate air pollution all around the world. With surface observations showing substantial decrease of criteria pollutants, including O3, NOx, CO and SO2, the long-term aircraft measurements over the eastern U.S. provide a unique opportunity to study the trend of the air pollutant column contents and the regional transport in the free troposphere. Analyses of the historical data indicated ~2.0 Dobson Unit/decade decrease in tropospheric O3 columns over the eastern U.S. with a similar decreasing trend of CO. The statistical analysis also showed a significant decreasing trend for tropospheric SO2. Analyses of the EPA CEMS emission data showed parallel reductions. A case study of tropospheric O3 and SO2 over downwind area of Baltimore showed that the regional transport by westerly wind from Ohio and Pennsylvania play an important role in the local air quality issues. As the second largest economy in the world, China's rapid economic growth in the last decade lead to a dramatic increase in energy demand, which relied heavily on coal burning. The enormous amount of SO2 emissions caused severe environmental issues including acid deposition and particulate matter pollution. To mitigate these air quality problems, strict control measures and regulations were applied to abate sulfur emissions, especially before and during the 2008 Beijing Olympics. Aircraft measurements of tropospheric SO2 were conducted over central China in spring 2008, where intense measurements are lacking. A substantial amount of SO2 was observed in the free troposphere, which is important to regional transport and remote sensing. I successfully validated the SO2 columns with satellite retrievals, and proved that the new OMI SO2 algorithm performs better than the conventional algorithm. An emission inventory was evaluated through a combination of model simulations and satellite products. Between 2006 and 2008, the SO2 emissions had been reduced substantially over middle and eastern China. I also analyzed the model simulations, and find the SO2 lifetime is ~ 38 h during spring in China and that ~50% of Chinese emissions are exported to the western Pacific.