Keywords: acid deposition, frequency–size distributions, power law, self-organised criticality
Power-law distribution of acid deposition
The scaling behaviour in acid deposition dynamics of 184 monitoring sites under the National Atmospheric Deposition Program (NADP) is analysed for the 1978–2001 period. The results show that: the distribution of weekly hydrogen deposition (WHD) is consistent with a power law in two different regimes separated by a crossover WHD (CWHD), and both the CWHD and its probability density increase as the power law commensurate with the mean of WHD series; the distribution of pH values shows a series behaviour similar to that of WHD and can be depicted as a log–linear model with the same form of Gutenberg–Richter model of earthquake occurrence; and the successive time-duration (weeks) of both acid and non-acid rain also obeys a power law, with the average duration of acid rain scaling as a positive power law and that of non-acid rain as a negative power law of average WHD. The power laws in the acid deposition dynamics are considered to be indicators of self-organisation of the atmosphere under environmental pollution stress.