A note on peak-to-mean concentration ratios |
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| Authors: | P J Barry |
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| Institution: | 1. Biology and Health Physics Division, Atomic Energy of Canada Limited, Chalk River Nuclear Laboratories, Chalk River, Ontario, Canada
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| Abstract: | The peak-to-mean concentration ratio obtained from observations near a point source of pollution is a particular example of the ratio of any short-period concentration to the long-term mean. The value of this ratio may be obtained from the probability distribution function: $$F(C) = F(0) exp - F(0) C/M]$$ whereF(C) is the probability or frequency that the ratio of a short-period average concentration (C) to the long-term mean (M) exceeds the valueC/M, andF(0) is a parameter dependent on the length of the short period and the position of the sampler relative to the centre-line of the plume. From (1) the peak-to-mean concentration ratio is shown to be related to the two averaging times by the expression $$P/M = 1/F(0) lnF(0) - lnt_M /t_P ]$$ wheret M andt P are, respectively, the averaging times of the long-term meanM and the short-term peakP. Using recently published experimental data, Equation (1) and hence also (2) are shown to be valid for averaging timest P from 5 s to 24 h and oft M from 6 min to 5 yr providedt P ?t M . |
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