Advection aerosol dispersion

It is desirable to calculate new bulk phase Z values for the four primary media which include the contribution of dispersed phases within each medium as described by Mackay and Paterson (1991) and as listed earlier. The air is now treated as an air-aerosol mixture, water as water plus suspended particles and fish, soil as solids, air and water, and sediment as solids and porewater. The Z values thus differ from the Level I and Level II pure phase values. The necessity of introducing this complication arises from the fact that much of the intermedia transport of the chemicals occurs in association with the movement of chemical in these dispersed phases. To accommodate this change the same volumes of the soil solids and sediment solids are retained, but the total phase volumes are increased. These Level III volumes are also given in Table 1.5.2. The reaction and advection D values employ the generally smaller bulk phase Z values but the same residence times thus the G values are increased and the D values are generally larger. 

The dominant transport mechanism for both aerosol and gaseous agents in the atmosphere is advection associated with the bulk motion of the atmosphere. Since airflows in the planetary boundary layer exhibit signihcant turbulence under most conditions (though turbulence may be suppressed under conditions of temperature inversion), this will cause aerosol releases to disperse into a plume or puff that expands... 

Since the dispersion of aerosols is driven primarily by advection, the sophistication and accuracy of the wind-field characterization provided to a model is the principal factor in determining the accuracy of the dispersion predictions provided by the model. This may range from ... 

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