David K. Heist

Screening Level Assessment of Risks Due to Dioxin Emissions from Burning Oil from the BP Deepwater Horizon Gulf of Mexico Spill

Between April 28 and July 19 of 2010, the U.S. Coast Guard conducted in situ oil burns as one approach used for the management of oil spilled after the explosion and subsequent sinking of the BP Deepwater Horizon platform in the Gulf of Mexico. The purpose of this paper is to describe a screening level assessment of the exposures and risks posed by the dioxin emissions from these fires. Using upper estimates for the oil burn emission factor, modeled air and fish concentrations, and conservative exposure assumptions, the potential cancer risk was estimated for three scenarios: inhalation exposure to workers, inhalation exposure to residents on the mainland, and fish ingestion exposures to residents. U.S. EPAs AERMOD model was used to estimate air concentrations in the immediate vicinity of the oil burns and NOAAs HYSPLIT model was used to estimate more distant air concentrations and deposition rates. The lifetime incremental cancer risks were estimated as 6 × 10(-8) for inhalation by workers, 6 × 10(-12) for inhalation by onshore residents, and 6 × 10(-8) for fish consumption by residents. For all scenarios, the risk estimates represent upper bounds and actual risks would be expected to be less.

Airflow Around a Child-Size Manikin in a Low-Speed Wind Environment

This work provides an understanding of how airflow patterns around humans can affect the concentrations and particle size distributions of particulate matter (PM) in the breathing zone. The focus of the experiments reported here is the flow around a child-size manikin under various conditions, including changes in body heat, breathing, wind speed, and body orientation relative to the wind direction. The airflow patterns that develop were investigated using laser Doppler anemometry. The presence of body heat changes the flow pattern most dramatically. With the manikin at room temperature, the flow pattern on the downstream side of the manikin consists of two slowly recirculating eddies. With the addition of body heat to the manikin, the flow pattern downstream of the manikin changes to a rising vertical plume with velocities on the order of 0.1 m/s. This vertical plume is capable of transporting PM into the breathing zone from near the floor. Increased wind speed decreases the relative importance of buoyancy. As the wind speed increases from 0.1 to 0.3 m/s, the vertical plume on the downstream side of the manikin is replaced by two recirculating eddies, a flow pattern similar to that with the unheated manikin. Changes in the relative importance of body heat and free-stream wind speed are quantified using a type of Richardson number.

The effect of a tall tower on flow and dispersion through a model urban neighborhood: part 1. Flow characteristics.

Wind tunnel experiments were performed to examine the effect of a tall tower on the flow around an otherwise uniform array of buildings. Additionally, preliminary CFD simulations were run to visualize the flow with more resolution. The model used in both the wind tunnel and CFD studies was designed to simulate an area of Brooklyn, NY, USA, where blocks of residential row houses form a neighborhood bordering a major urban highway. This area was the site of a field study that, along with the work reported here, had the goal of improving the understanding of airflow and dispersion patterns within urban microenvironments. Results reveal that a tall tower has a dramatic effect on the flow in the street canyons in the neighboring blocks, enhancing the exchange between the street canyon flow and the freestream flow aloft. In particular, vertical motion down the windward side and up the leeward side of the tower resulted in strong flows in the lateral street canyons and increased winds in the street canyons in the immediate vicinity of the tower. These phenomena were visible in both the wind tunnel and CFD results, although some minor differences in the flow fields were noted.

Air Quality Modeling in Support of the Near-Road Exposures and Effects of Urban Air Pollutants Study (NEXUS)

A major challenge in traffic-related air pollution exposure studies is the lack of information regarding pollutant exposure characterization. Air quality modeling can provide spatially and temporally varying exposure estimates for examining relationships between traffic-related air pollutants and adverse health outcomes. A hybrid air quality modeling approach was used to estimate exposure to traffic-related air pollutants in support of the Near-Road Exposures and Effects of Urban Air Pollutants Study (NEXUS) conducted in Detroit (Michigan, USA). Model-based exposure metrics, associated with local variations of emissions and meteorology, were estimated using a combination of the American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) and Research LINE-source dispersion model for near-surface releases (RLINE) dispersion models, local emission source information from the National Emissions Inventory, detailed road network locations and traffic activity, and meteorological data from the Detroit City Airport. The regional background contribution was estimated using a combination of the Community Multi-scale Air Quality (CMAQ) and the Space-Time Ordinary Kriging (STOK) models. To capture the near-road pollutant gradients, refined “mini-grids” of model receptors were placed around participant homes. Exposure metrics for CO, NOx, PM2.5 and its components (elemental and organic carbon) were predicted at each home location for multiple time periods including daily and rush hours. The exposure metrics were evaluated for their ability to characterize the spatial and temporal variations of multiple ambient air pollutants compared to measurements across the study area.

Development of a Versatile Aerosol Generation System for Use in a Large Wind Tunnel

A novel aerosol generation system has been constructed for use in a large wind tunnel for two distinct research projects. One project requires a uniform aerosol concentration over the wind tunnel cross section, while the other project demands a stratified aerosol concentration distribution. The system consists of an array of venturi nozzles, which entrains particulate matter from a moving conveyor belt and disperses it into the tunnel under the force provided by a compressed air source. For the stratified release configuration, only the bottom row of nozzles was used and a confinement sleeve was installed to prevent mixing with clean air; the mixing fans were omitted from this configuration. The uniform release arrangement was tested by gravimetrically measuring particle concentration over the cross section of the tunnel for tunnel speeds of 0.1 and 1.0 m/s; uniformity was achieved within a coefficient of variation of 6.4%. The stratified distribution results show a high concentration near the floor, which diminishes with increased height. Particle size distribution was also determined on filter samples using scanning electron microscopy analysis for the uniform release experiments. No appreciable difference in mass median diameter or geometric standard deviation could be discerned for the various sampling points.

Methodology for siting ambient air monitors at the neighborhood scale.

Abstract In siting a monitor to measure compliance with U.S. National Ambient Air Quality Standards (NAAQS) for par-ticulate matter (PM), there is a need to characterize variations in PM concentration within a neighborhood-scale region to achieve monitor siting objectives. A simple methodology is provided here for the selection of a neighborhood-scale site for meeting either of the two objectives identified for PM monitoring. This methodology is based on analyzing middle-scale (from 100 to 500 m) data from within the area of interest. The required data can be obtained from widely available dispersion models and emissions databases. The performance of the siting methodology was evaluated in a neighborhood-scale field study conducted in Hudson County, NJ, to characterize the area’s inhalable particulate (PM10) concentrations. Air monitors were located within a 2- by 2-km area in the vicinity of the Lincoln Tunnel entrance in Hudson County. Results indicate the siting methodology performed well, providing a positive relationship between the predicted concentration rank at each site and the actual rank experienced during the field study. Also discussed are factors that adversely affected the predictive capabilities of the model.

On the Impact of the Human (Child) Microclimate on Passive Aerosol Monitor Performance

Research into the wind microclimate and its effect on the accuracy and effectiveness of passive aerosol monitors is expanding as the importance of personal monitoring versus regional monitoring increases. The important phenomena for investigation include thermal and dynamic effects of the human body, contaminant dispersion around a human body and within a building complex, and the wind environment within a building (indoor/outdoor) complex. This paper demonstrates that the microclimate around the human body plays a critical role in contaminant transport near the body and thus can affect particle concentration measurements by personal samplers.

Enhancements to AERMOD's building downwash algorithms based on wind-tunnel and Embedded-LES modeling

Knowing the fate of effluent from an industrial stack is important for assessing its impact on human health. AERMOD is one of several Gaussian plume models containing algorithms to evaluate the effect of buildings on the movement of the effluent from a stack. The goal of this study is to improve AERMODs ability to accurately model important and complex building downwash scenarios by incorporating knowledge gained from a recently completed series of wind tunnel studies and complementary large eddy simulations of flow and dispersion around simple structures for a variety of building dimensions, stack locations, stack heights, and wind angles. This study presents three modifications to the building downwash algorithm in AERMOD that improve the physical basis and internal consistency of the model, and one modification to AERMODs building pre-processor to better represent elongated buildings in oblique winds. These modifications are demonstrated to improve the ability of AERMOD to model observed ground-level concentrations in the vicinity of a building for the variety of conditions examined in the wind tunnel and numerical studies.

Numerical analysis of pollutant dispersion around elongated buildings: An embedded large eddy simulation approach

High fidelity, scale-resolving numerical simulations of flow and pollutant dispersion around several elongated isolated buildings are presented in this paper. The embedded large eddy simulation (ELES) is used to model flow and concentration fields for six test cases with various source-building geometries. Specifically, the influence of building aspect ratio, wind direction, and source location is examined with these cases. Results obtained from the present ELES model are evaluated using available wind tunnel measurements, including those of streamwise and spanwise velocities, turbulent kinetic energy, and streamwise, lateral, and spanwise pollutant concentrations. Comparisons indicate that the ELES provides realistic representations of the flow and concentration fields observed in wind tunnel experiments, and captures several complex phenomena including the lateral shift and enhanced descent of the plume for rotated/elongated buildings. Furthermore, the ELES provides a means to study the advective and turbulent concentration fluxes, plume shapes, and geometry of vortical structures that is used to examine turbulent transport of pollutants around buildings. We investigate the enhancement of vertical and lateral plume spread as the building aspect ratio is increased. In addition, through the study of advective and turbulent concentration fluxes, we shed light on the physics behind higher ground-level concentrations observed for rotated buildings.

Development and evaluation of the R-LINE model algorithms to account for chemical transformation in the near-road environment

With increased urbanization, there is increased mobility leading to higher amount of traffic-related activity on a global scale. Most NOx from combustion sources (about 90-95%) are emitted as NO, which is then readily converted to NO2 in the ambient air, while the remainder is emitted largely as NO2. Thus, the bulk of ambient NO2 is formed due to secondary production in the atmosphere, and which R-LINE cannot predict given that it can only model the dispersion of primary air pollutants. NO2 concentrations near major roads are appreciably higher than those measured at monitors in existing networks in urban areas, motivating a need to incorporate a mechanism in R-LINE to account for NO2 formation. To address this, we implemented three different approaches in order of increasing degrees of complexity and barrier to implementation from simplest to more complex. The first is an empirical approach based upon fitting a 4th order polynomial to existing near-road observations across the continental U.S., the second involves a simplified two-reaction chemical scheme, and the third involves a more detailed set of chemical reactions based upon the Generic Reaction Set (GRS) mechanism. All models were able to estimate more than 75% of concentrations within a factor of two of the near-road monitoring data and produced comparable performance statistics. These results indicate that the performance of the new R-LINE chemistry algorithms for predicting NO2 is comparable to other models (i.e. ADMS-Roads with GRS), both showing less than ±15% fractional bias and less than 45% normalized mean square error.