Browsing by Author "Dr. Dev Niyogi, Committee Co-Chair"

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    Trends in Agricultural Ammonia Emissions and Ammonium Concentrations in Precipitation over the Southeast and Midwest United States
    (2006-10-06) Konarik, Stephen Brian; Dr. Pal Arya, Committee Member; Dr. Viney P Aneja, Committee Co-Chair; Dr. Dev Niyogi, Committee Co-Chair
    Emissions from agricultural activities, both crop and animal, are known to contain gaseous ammonia (NH3) which through chemical reaction in rainwater changes into ammonium ion (NH4+). Using wet deposition data of ammonium from several National Atmospheric Deposition Program/National Trends Network (NADP⁄NTN) and Clean Air Status Trends Network (CASTNet) sites, as well as calculated ammonia emissions from North Carolina and the Southeast and Midwest regions of the United States, trends in ammonium concentrations in precipitation were analyzed for the period of 1983-2004. In addition, HYSPLIT back-trajectory model was used to determine that when ambient air in downwind sites arrived from the high ammonia emissions source region, ammonium concentrations in precipitation were enhanced. For the Southeast United States domain, analysis shows that NH4+ concentrations generally increased with increasing NH3 emissions from within the same region. Similar analysis has been performed over the Midwest United States and compared to the results from the Southeast United States. Emissions from the Midwest are attributed to larger animals, including hogs and cattle, whereas the Southeast has a higher percentage of emissions coming from smaller livestock, such as chickens. In addition, the Midwest United States region has a much more uniform spatial distribution of emissions. The conversion of ammonia gas (NH3) into ammonium ion (NH4+) is a fundamental process that is of great environmental significance. Excessive amounts of NH4+ can lead to acidification of soils and other pollution problems. An agricultural ammonia emissions inventory for the Midwest United States and Southeast United States was developed using data from the United States Department of Agriculture 2002 Census. This inventory indicates total annual ammonia emissions to be nearly the same over the two regions, with 1417 X 106 kg NH3⁄km2⁄year over the Southeastern United States and 1691 X 106 kg NH3⁄km2⁄year over the Midwestern United States. The emission rates are similar to those of model simulations from the Carnegie Mellon University Ammonia Model. Comparing these rates to the ammonium ion concentration and wet deposition obtained from the National Atmospheric Deposition Program (NADP) monitoring network reveals discrepancies from the results projected by the emissions inventory. The NADP network shows deposition rates of ammonium over the Southeast U.S. region at nearly twice those of the Midwest U.S. region. These contrasts have been explored and reasons for the differences are discussed. The beginning of 1997 coincides with the implementation of a moratorium on new hog farms in the state of North Carolina. Results from the analysis in North Carolina indicate a lessening in the rate of increases in NH4+ concentration in precipitation since the moratorium went into effect. Sampson County, NC, saw stable ammonium ion concentrations from 1983-1989, an average rise of 9.5% from 1989-1996, and an average increase of only 4% from 1997-2004. In analyzing the trends in NOx, the effect of implementation of the Clean Air Act Amendments of 1990 is clearly seen in the precipitation chemistry as well.
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    Urban Land-surface Impacts on Convective Thunderstorm and Precipitation Characteristics
    (2006-11-01) Pyle, Patrick Chase; Dr. Dev Niyogi, Committee Co-Chair; Dr. S. Pal Arya, Committee Co-Chair; Dr. Viney Aneja, Committee Member
    A six year storm climatology in the Indianapolis, Indiana region is investigated using base reflectivity radar data. Severe storm reports provided by the Storm Prediction Center (SPC) are used to select relevant thunderstorm cases to study. Storm composition change was noted in urban and rural environments and further statistical analysis is performed to view the overall effect of the urban region on storm characteristics. A specific thunderstorm case on 13 June 2005 is further examined using the fifth-generation NCAR/Penn State Mesoscale Model (MM5) V3.7.2. The Noah Land Surface Model (LSM) is used to represent the urban environment with a sensitivity simulation removing the urban region and replacing it with the dominant rural land use category. Results show a drastic change in surface energy balance characteristics as well as model derived radar reflectivity patterns when the urban region is removed in the NOURBAN simulation. The same 13 June 2005 case is also investigated using the Weather Research and Forecasting (WRF) V.2.1.1 model. Identical control and nourban simulations are performed similar to the MM5. Results between the two mesoscale models are difficult to compare due to the domain structure as well as the different physics options and data initialization techniques used within the two models; however, few comparisons can be made. Several land use sensitivity simulations are also performed in an effort to better understand the underlying effects of the urban region on the case of interest. Simulations include a nourban case where the urban region is completely removed and replaced by the dominate surrounding rural land use, similar to the MM5 study. Other simulations performed are used to set up a statistical factor separation experiment. Land use variables that are manipulated include albedo, surface roughness length (z0), and urban sprawl. All variables are manipulated to increase the overall effectiveness of a larger, more 'robust' city (Indianapolis) to resemble the current and projected increase in urbanization. Model comparisons within these simulations were compared using only the nest 3 (4 km) resolution due to the poor representation of the event on the finest 1.33 km grid spacing nest. Surface energy balance parameters were not altered a great deal in the simulations; however, the overall precipitation patterns and storm characteristics show a wide range of variability. When the urban region is removed, the storm of interest does not propagate through the urban region. Accumulated precipitation totals through the time of the event are dramatically less around and downwind (northeast) of the urban region. The factorial experiment suggested that a more robust city acted to place the maximum precipitation amounts on the northern lateral edge of the city that may be caused by the urban 'building barrier effect.' Observations from the Joint Urban Project 2003 held in Oklahoma City are used to compare to the Coupled Ocean-Atmosphere Mesoscale (COAMPS) model sensitivity simulations of a Mesoscale Convective System (MCS) event that occurred on 30 July 2003. Two distinct simulations were used to compare the control simulation. The OKC urban region was enhanced by using a coupled urban canopy model (UCM) approach to attempt to resolve the finer scale heating and drag features of the urban environment (e.g., roof, wall, street, and anthropogenic heating contributions) to the urban heat island (UHI). Also, the Gas Exchange Photosynthesis Based model (GEM) was coupled to the Noah Land Surface Model (LSM) to enhance the overall heterogeneity of the urban-rural interface. Results indicate that the simulation with urban canopy parameterizations (UCP) enhanced the overall intensity of the event, while the GEM proved to show more heterogeneity by placing the convection away from the downtown area, similar to the observed.