5.0 AIR AS SOURCE

        The air-as-source component is an input option that allows the investigator to input a uniform regional air concentration of a contaminant. The exposure pathways are computed based on having the same concentrations and deposition rate everywhere over the region. That is,
 


where C(x,q) is the air concentration at any arbitrary distance, x, and direction,q(degrees); and Ci is the input value for ambient air concentrations (g/m³).
 
        Applications for the air-as-source component are mainly for evaluation of background concentrations from sources of distant and/or poorly defined origin. The air-as-source component may also be used to approximately evaluate impacts from a disperse regional source term such as roadways.