Empirical dosage-distance relationships around a point source

Empirical dosage-distance relationships around a point source—at ground level

Benarie, M.M.

Abstract To compute pollutant dosage (i.e. the product of the concentration by exposure time), first the concentration is evaluated as a function of distance, wind and stability parameters, etc. Then, concentration is averaged over the fluctuating plume. This second step also involves some theory and some more assumptions about atmospheric properties. This paper shows, that the published literature contains a body of information which permits one to relate empirically the dosage around a ground level point source to the distance, in an elementary way. Fragmentary observations were linked by a general formula, spanning the distance from tens of m to tens of km. Moreover, this empirical approach shows that wind velocity from near calm to tens of m s⁻¹, the presence or absence of obstacles and of terrain roughness and even sampling duration (between 15 and 60 min) play no noticeable role. Only two stability conditions (day and night) cover all possible cases. The absence of all theory from this approach must especially be stressed: it might even be said, that the obvious pragmatical evidence supersedes many a complex theory. The two simple formulae, D (dosage, normalized to unit emission) = 7.3 x ⁻² (day)D = 25 x ⁻² (night), where x is the downwind distance (m), seem to cover all possible cases.