UC Riverside

This dissertation summarizes the results from the development and application of models to investigate the transport and dispersion of pollutants from two major sources. In the first study, I formulate and apply a dispersion model to estimate emissions of methane from manure dairy lagoons, In the second, I examine the role of noise barriers in mitigating the impact of vehicular emissions on near-road air quality. I also present the development and application of a semi-empirical meteorological model to compute meteorological inputs required by dispersion models using measurements from instruments that are simpler and less cumbersome than those being used now.Manure lagoons in dairies make significant contributions to emissions of methane, a major greenhouse gas. Because there is no direct method to estimate these emissions, a variety of methods have been developed to infer these emissions from concentration measurements made close to lagoons. My research involves developing such an inference approach based on a state-of-the-art dispersion model combined with a unique sampling strategy. My approach also allows for estimating the uncertainty in these emission estimates. I demonstrate my approach by applying it to estimating methane emissions from two manure lagoons, one located in southern California and the other in northern California. I compare my results with those obtained from a popular approach based on a Lagrangian particle dispersion model. Air pollution associated with vehicle emissions from roadways has been linked to a variety of adverse health effects on people living within 100 m of roadways. Wind tunnel and tracer studies indicate that near-road noise barriers have a mitigating impact on air pollution caused by vehicular emissions. Data from these studies formed the basis of a barrier model that accounted for this mitigating effect. This model has been incorporated into a research version of AERMOD, a model recommended by the USEPA for estimating the impact of a variety of pollution sources including highways. Before AERMOD can be used for regulatory applications that give credit for the mitigating effect of noise barriers, the barrier component of the model must be evaluated with real-world data with its attendant complexities that were absent in the controlled wind tunnel and tracer studies. I made significant contributions to the design and conduct of a comprehensive field study that UCR conducted to collect the data required to evaluate the performance of the barrier component of AERMOD. An analysis of the data indicates that AERMOD is likely to underestimate mitigation from barriers at low wind speeds. We suggest an approach to correct this problem. Currently used dispersion models require meteorological inputs that are best computed with time-resolved velocity and temperature measurements made with 3-D sonic anemometers. Because such measurements are not routinely available, there is a need for methods that provide accurate estimates of these inputs using equipment that is easy to set up and provides measurements that can be readily interpreted. I demonstrate such a method based on measurements of horizontal wind speeds and temperature fluctuations. The method is evaluated by comparing methane emissions from a dairy manure lagoon inferred from a dispersion model that uses modeled meteorological inputs to those from measurements with a 3-D sonic anemometer. We show that this method can be adapted for temperature fluctuations measured with a low-cost temperature sensor that is unable to resolve the high-frequency temperature fluctuations captured by sonic anemometers.