Implementation and evaluation of bulk Richardson number scheme in AERMOD

The AERMOD dispersion model was designed to accept a wide range of site-specific meteorological measurements, including profiles of wind, temperature and turbulence data. However, the algorithm for estimating the heat flux under stable conditions requires a cloud cover measurement, which is not typically available from site-specific monitoring programs. For applications of AERMOD in remote settings, the non-representativeness of cloud cover measurements from the nearest airport station may present an obstacle to the application of AERMOD. An alternative scheme for estimating heat flux under stable conditions based on the use of low-level delta-T measurements, referred to as the Bulk Richardson Number Scheme, has been implemented in the AERMET meteorological processor. This paper will present results of a technical review and modification of the implementation of the Bulk Richardson Number Scheme in AERMET, and results of an evaluation of the AERMOD model performance using the modified Scheme as compared to the use of cloud cover data.