Acidic deposition to forests: The 1985 chemistry of high elevation fog (CHEF) project

Abstract

The literature supporting significant water deposition directly from cloud and fog to the earth's surface is reviewed and previous aircraft and surface measurements of the acidity of this water are summarized. An overview of recent work on forest decline is given and an American (Mountain Cloud Chemistry Project) and Canadian (Chemistry of High Elevation Fog) program to look at the chemical deposition by clouds to high elevation forests, is‐described. Preliminary measurements in late 1985 on two mountains in Quebec indicate that fog (cloud on the mountain) water pH values (≈3.8) near the summits (850–970 m) are much lower than precipitation pH values (≈ 4.3) at the same location; the summits are estimated to be in cloud 44% of the year with lower percentages at lower elevations; an estimate of total annual fog water deposition (77 cm) near the summit is similar to the average annual precipitation in Quebec; the estimated fog water hydrogen ion deposition (135 meq m⁻²) is about three times that from the precipitation; the precipitation pH values may be lower (4.1 ver sus 4.3) at lower elevations with precipitation amounts perhaps 50% higher at higher elevations.