Comparison study in mixing height determination for dispersion models

Abstract

Hungarian Transmission Standards were updated with the goal of standardising and improving methods for the calculation of meteorological parameters used as inputs in air quality dispersion models. New methods for determining mixing height are recommended by COST 710. For stable and mechanically dominated unstable atmospheric boundary layers, the formula for determining mixing height requires friction velocity, Monin-Obukhov length and Coriolis parameter. For convective boundary layers, a simple prognostic model based on the determination of initial temperature profile, surface momentum and sensible heat fluxes is used. Statistical comparisons among (i) new and (ii) former Hungarian Standards, (iii) AERMOD, (iv) some methods suggested by COST 710 as well as (v) mixing height calculation from radiosonde measurements were performed. Hourly values of mixing height were calculated based on standard meteorological measurements using the different approaches given above for a one-year dataset (1996). Model results for the new Hungarian Standards are in good agreement with radiosonde measurements; the best fit was obtained during periods of a growing convective layer. The growth rate of the mixing layer height is found to be sensitive to the potential temperature gradient above the convective layer.