Effect of atmospheric stability on concentration fluctuations and wake retention times for dispersion in the vicinity of an isolated building

This study is concerned with the effect of changes in atmospheric stability on concentration fluctuations near an isolated building. Field experiments were conducted to measure concentration fluctuations at several locations close to a model building, for continuous point sources upwind of the building. Experiments were conducted in flat terrain using a 2 m cube as the model. Concentrations were measured at a frequency of 200 Hz using a detector system with a response time of 1/50 second. Meteorological conditions varied from stable to unstable. Analysis of the time series of concentration produced by these experiments has shown that there are several periods when the gas behaves as if it were switched off at the source (due to shifts in the wind direction). Comparisons were made in such cases of the time taken for the source gas to evacuate the wake recirculation region. It was found that this period was several times longer in stable meteorological conditions than in unstable conditions. This finding has important implications in relation to hazard assessment near buildings.

[1]  David J. Ride,et al.  A practical method of estimating toxic loads in the presence of concentration fluctuations , 1995 .

[2]  N. Mole,et al.  Concentration fluctuation data from dispersion experiments carried out in stable and unstable conditions , 1994 .

[3]  P. Drivas,et al.  Probing the air flow within the wake downwind of a building by means of a tracer technique. , 1974, Atmospheric environment.

[4]  J. Vincent.  Model experiments on the nature of air pollution transport near buildings , 1977 .

[5]  T. G. McRae,et al.  Analysis of Burro series 40-m3 lng spill experiments , 1982 .

[6]  D. J. Hall,et al.  Concentration measurements around an isolated building: A comparison between wind tunnel and field data , 1994 .

[7]  K. Mylne,et al.  Concentration fluctuation measurements in a plume dispersing in a stable surface layer , 1992 .

[8]  Christopher D. Jones,et al.  Full-scale experiments on dispersion around an isolated building using an ionized air tracer technique with very short averaging time , 1984 .

[9]  J. Fackrell,et al.  Parameters characterising dispersion in the near wake of buildings , 1984 .

[10]  Richard Griffiths,et al.  The effect of uncertainties in human toxic response on hazard range estimation for ammonia and chlorine , 1984 .

[11]  W. Hinds.  Peak-to-mean concentration ratios from ground-level sources in building wakes☆ , 1969 .

[12]  P. J. Mason,et al.  Concentration fluctuation measurements in a dispersing plume at a range of up to 1000 m , 1991 .