Fluctuating concentrations in atmospheric dispersion

This thesis presents theoretical models and experimental results of average and instantaneous concentration measurements from a series of atmospheric dispersion experiments conducted under both unstable and stable meteorological conditions. The experiments were undertaken at two different sites, over both flat and gently rolling terrain. Two types of surface-level point aerosol sources were used. One is a fog-oil smoke and the other is a hexachloroethane chemical smoke. Measurements of concentration at points along crosswind transects were taken over time periods of an hour at distances to several kilometers from the source. These measurements included both aerosol photometer records of the instantaneous concentration taken at a 1 Hz sampling rate and aspirated filters for mean concentration measurements.The flat terrain site was located at Camp Atterbury, Indiana, while the gently rolling terrain site was near Red Bluff, California. Meteorological measurements at these sites included both tower measurements and upper-air balloon soundings. These measurements were used in determining the atmospheric boundary layer scaling parameters in the unstable tests and in characterizing the complex wind field for the stable tests.The data compare favorably with developed models for both the mean and variance in concentration. Concentration fluctuation intensity ranges from 2 near the plume centerline to greater than 20 at the plume edge. Intermittency is important at all locations, with positive concentrations recorded on the mean plume centerline only 20% to 50% of the time. Point concentration histograms are shown to agree with the exponential distribution for concentrations greater than zero.Spectra of the concentration data show an inertial-convective subrange with a $-$5/3 power law versus frequency behavior. Integral time scales of the concentration records at all individual sampling points are approximately constant within a test and are equal to the mean duration of episodes or bursts in which the concentration is greater than zero. The probability distribution of individual burst durations at each sampler shows an exponential distribution.U of I OnlyETDs are only available to UIUC Users without author permissio

An Excel®-Based Visualization Tool of Two-Dimensional Soil Gas Concentration Profiles in Petroleum Vapor Intrusion

In this study, we present a petroleum vapor intrusion (PVI) tool implemented in Microsoft((R)) Excel((R)) using Visual Basic for Applications and integrated within a graphical interface. The latter helps users easily visualize two-dimensional soil gas concentration profiles and indoor concentrations as a function of site-specific conditions such as source strength and depth, biodegradation reaction rate constant, soil characteristics and building features. This tool is based on a two-dimensional explicit analytical model that combines steady-state diffusion-dominated vapor transport in a homogeneous soil with a piecewise first-order aerobic biodegradation model, in which rate is limited by oxygen availability. As recommended in the recently released United States Environmental Protection Agency's final PVI guidance, a sensitivity analysis and a simplified Monte Carlo uncertainty analysis are also included in the spreadsheet

A two-dimensional analytical model of petroleum vapor intrusion

In this study we present an analytical solution of a two-dimensional petroleum vapor intrusion model, which incorporates a steady-state diffusion-dominated vapor transport in a homogeneous soil and piecewise first-order aerobic biodegradation limited by oxygen availability. This new model can help practitioners to easily generate two-dimensional soil gas concentration profiles for both hydrocarbons and oxygen and estimate hydrocarbon indoor air concentrations as a function of site-specific conditions such as source strength and depth, reaction rate constant, soil characteristics and building features. The soil gas concentration profiles generated by this new model are shown in good agreement with three-dimensional numerical simulations and two-dimensional measured soil gas data from a field study. This implies that for cases involving diffusion dominated soil gas transport, steady state conditions and homogenous source and soil, this analytical model can be used as a fast and easy-to-use risk screening tool by replicating the results of 3-D numerical simulations but with much less computational effort