The “airshed” concept and its application in complex terrain

A review of the term “airshed” suggests that it should be defined in a functional manner. Where the concept is applied to complex terrain, the degree and frequency of coupling between valley airflows and those at higher altitudes is a key to the delineation of airshed boundaries. In cases where decoupling is very frequent, observational data of vertical temperature structure or wind velocity and direction, or both, may be used to determine the upper boundary for valley airsheds. This is demonstrated for two valleys in N.W. Colorado.