Building wake dispersion at an Arctic industrial site: Field tracer observations and plume model evaluations

AtlftOspheric Environment Vol. 24A, No. 9, pp. 2329- 2347, 1990. Printed in -Great Britain. Pergamon Press pie BUILDING WAKE DISPERSION AT AN ARCTIC INDUSTRIAL SITE: FIELD TRACER OBSERVATIONS AND PLUME MODEL EVALUATIONS ALEX GUENTHER, BRIAN LAMB* and EUGENE ALLWINE Laboratory for Atmospheric R~search, Department of Civil & Environmental Engineering, Washington State University, Pullman, WA 99164-2910, U.S.A. (First received 8 June 1989 and in final form 21 February 1990) Abstract-Ten multi-hour atmospheric dispersion SF 6 tracer experiments were conducted during October and November of 1987 near a large oil gathering facility in the Prudhoe Bay, Alaska, oilfield reservation. The purpose of this study was to investigate dispersion under arctic conditions and in situations where building- generated airflow disturbances dominate downwind distributions of ground level pollutant concentrations. This was accomplished with a network of micrometeorological instruments, portable syringe tracer samplers, continuous tracer analyzers, and infrared visualization of near source plume behavior. Atmospheric stability and wind speed profiles at this arctic site are influenced by the smooth (surface roughness=0.03 cm), snow covered tundra surface which receives negligible levels of solar isolation in winter. The dispersion of pollutants emitted from sources within the oil gathering facility, however, is dominated by the influence of nearby buildings when high winds generate elevated ground level concentrations. An order of magnitude increase in maximum ground level concentration was observed as wind speeds increased from 5 to 8 ms - 1 and another order of magnitude increase was observed as winds increased from 8 to 16ms - 1 . Variation in maximum concentrations was also observed with changes in wind direction. Vertical plume diffusion (a,) near the buildings was a factor of 2-3 greater than that observed in open terrain and was dependent on both wind speed and the projected building width and location of nearby buildings. Wind tunnel tracer distributions for east winds agree with field observations but also indicate that a significant increase in plume downwash occurs with other wind directions. Concentration distributions were calculated using several versions of the Industrial Source Complex (ISC) model. Model estimates of ground level concentrations were within a factor of three depending on wind direction. The model predictions are extremely sensitive to the ratio of plume height to vertical plume diffusion which is significantly influenced by a complex aerodynamic wake in the field. Key word index : Arctic, dispersion, tracer, downwash, buildings, plume rise, ISC. 1. INTRODUCTION The development and evaluation of air quality modeling techniques have greatly benefited from transport and diffusion field studies. These include early experiments using smoke visualization techni- ques (Richardson, 1920); the classical large scale, open terrain diffusion experiments such as Project Prairie Grass (Haugen, 1959) which provide the empirical basis for the Pasquill-Gifford (PG) curves used in current regulatory air quality models; and more recent investigations of sites and conditions which deviate from the relatively simple dispersion environment of earlier experiments. In this paper we present the results of a field tracer investigation of plume trans- port and diffusion near the clustered and intercon- nected buildings of an arctic industrial complex. The natural gas compressor turbine which was the focus of this field study is typical of the major NOx sources in the Prudhoe Bay, Alaska, oilfields. Accurate simu- *To whom correspondence should be addressed. lation of pollutant dispersion from existing sources will aid in determining the present air quality within this tundra ecosystem and is needed for predicting the impacts of future development within potential oil- fields along the Alaska coast. We have previously analyzed open terrain micro- meteorological and tracer data collected at Prudhoe Bay to provide a description of the Arctic atmospheric boundary layer (Guenther and Lamb, 1990). Near the oil gathering facilities, building-generated disturban- ces to the flow field around the exhaust stacks signific- antly change dispersion patterns by altering mean airflow streamlines and by increasing turbulence lev- els. Maximum concentrations can increase signific- antly as high winds generate downwash conditions around the low turbine and heater stacks typical of an arctic industrial complex. Field observations of plume behavior from a 35 MHP turbine are described and compared to our analysis of a wind tunnel simulation of the same source and surrounding buildings (Guen- ther et al., 1989). Building downwash, diffusion, and plume rise algorithms in existing Gaussian plume models and cavity wake models are evaluated in this