Fog chemistry at an urban midwestern site

The Holcomb Research Institute is monitoring fog chemistry in Indianapolis, Indiana and at sites in and near the heavily industrialized Ohio River Valley. Results reported here indicate that fogs in this area can be strongly acidic, and that further studies are warranted. We report 1) the ionic composition of three fog events, samples collected in Indianapolis between December 1985 and February 1986, and 2) the pH of three additional events, samples collected between November 1985 and February 1986. (The volume of fog collected during the latter three events was insufficient for chemical analysis other than pH.) The pH of the fog samples ranged from 2.85 to 4.06; some of this fell within the range known to damage foliage and yield of some plant species. It has been demonstrated that even one exposure to highly acidic mists (pH par. delta 2.5) can damage certain crop species; hence, it is important to document the occurrence of any events having acidity near this level.