AERMOD: A Dispersion Model for Industrial Source Applications. Part I: General Model Formulation and Boundary Layer Characterization

Abstract

The formulation of the American Meteorological Society (AMS) and U.S. Environmental Protection Agency (EPA) Regulatory Model (AERMOD) Improvement Committee’s applied air dispersion model is described. This is the first of two articles describing the model and its performance. Part I includes AERMOD’s characterization of the boundary layer with computation of the Monin–Obukhov length, surface friction velocity, surface roughness length, sensible heat flux, convective scaling velocity, and both the shear- and convection-driven mixing heights. These parameters are used in conjunction with meteorological measurements to characterize the vertical structure of the wind, temperature, and turbulence. AERMOD’s method for considering both the vertical inhomogeneity of the meteorological characteristics and the influence of terrain are explained. The model’s concentration estimates are based on a steady-state plume approach with significant improvements over commonly applied regulatory dispersion models. Complex terrain influences are provided by combining a horizontal plume state and a terrain-following state. Dispersion algorithms are specified for convective and stable conditions, urban and rural areas, and in the influence of buildings and other structures. Part II goes on to describe the performance of AERMOD against 17 field study databases.

Ozone and its potential control strategy for Chon Buri city, Thailand

“…We used the meteorological processor of the advanced air pollutant dispersion model system AERMOD (U.S. EPA, 2004;Cimorelli et al, 2005), namely, AERMET, to compute those mixing heights. Before implementing AERMET, certain land-related characteristics of the study area (referenced at around the center of the domain) were prespecified using the AERMOD land-surface preprocessor (namely, AERSURFACE) (U.S. EPA, 2008), together with the LDD land cover data and a 42-yr (1961-2002) daily rain data set ( Table 1).…”

Performance of Steady-State Dispersion Models Under Low Wind-Speed Conditions

“…AERMOD (Cimorelli et al 2005) uses the following formulation to estimate the ground-level concentration from a surface release during stable conditions:…”

“…Under low wind speeds, horizontal meandering of the wind spreads the plume over large azimuth angles, which might lead to concentrations upwind relative to the vector-averaged wind direction. AERMOD (Cimorelli et al 2005), and other currently used regulatory models (Atmospheric Dispersion Modelling System (ADMS), Carruthers et al 1994), attempt to treat this situation by assuming that when the mean wind-speed is close to zero, the horizontal plume spread covers 360 • . Then, the concentration is taken to be a weighted average of concentrations of two possible states: a random spread state and a plume state.…”

“…It is generally believed that commonly used steady-state Gaussian dispersion models, such as AERMOD (Cimorelli et al 2005) are not applicable to situations when the wind speeds close to the ground are comparable to the standard deviation of horizontal velocity fluctuations. Under these conditions, the time scale of wind meandering is large compared to the W. Qian (B) · A. Venkatram Mechanical Engineering, University of California, Riverside, A343 Bourns Hall, 900 University Ave., Riverside, CA 92507, USA e-mail: windqian@gmail.com usual averaging time of 1 h, and consequently the horizontal concentration distribution is far from Gaussian.…”

“…van Ulden 1978), and represents the best available steady-state model. The performance of this model is compared with that of AERMOD (Cimorelli et al 2005), the regulatory model recommended by the U.S. Environmental Protection Agency, which represents the current generation of dispersion models used in regulatory applications. The next section provides relevant details of these two models.…”