A note on the consumption of acid through cation exchange with clay minerals in atmospheric precipitation

The first estimates of the consumption of potentially available strong acid in atmospheric precipitation through the mechanism of cation exchange with clay minerals have been obtained for three climatically different regions of the world: (1) Antarctica (South Pole); (2) continental Europe (north of the Alps); and (3) the continental Mediterranean.From the calculations involving the ranges of the concentrations of potentially available strong acid and of clay minerals of low-to-medium cation exchange capacity for each of the three regions it is suggested that the above process of acid consumption may almost always be insignificant in liquid (or liquified) precipitation over Antarctica and continental Europe.On the other hand, it is only under the most favourable conditions—involving the maximum stipulated cation exchange capacity of the clay minerals—that the same process could possibly lead to a maximum acid consumption in precipitation water up to ∼30% in the eastern Mediterranean region.The cation exchange process is also considered briefly in relation to the probable recycling of clay minerals of aeolian origin through evaporating clouds. Application of the first principles of cloud physics to the qualitative discussion suggests that clay minerals acting as freezing nuclei may have the best chance of participating in cation exchange, and hence, in acid consumption in clouds.