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 (i) 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; (ii) 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 (iii) 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-organization of the atmosphere under environmental pollution stress.