Leslie Roberts

Studies Probe Unexplained Decline in Eastern Forests

About two decades ago, the productivity of many eastern US forests declined abruptly. Since then, several tree species have been growing at extremely low rates, sometimes 40% below normal. No one is sure what precipitated it. Both natural factors and air pollution, particularly acid rain, are suspected. The natural factors suspected are prolonged drought that afflicted most of the East during the 1960s, and the unusually cold winters of the 1960s. The decline has occurred in areas thought to receive moderate to heavy rates of acid deposition. The amount of acid deposition, in all forms, is considerably greater in high-elevation forests, where forest decline and mortality are also the most severe. Some of these forests are exposed to high levels of ozone and heavy metals as well. It is too soon to say which, if any, of these factors is to blame, or if perhaps they act in concert - pollution making the trees more susceptible to natural stresses, or vice versa.

A Foggy Threat: California's Fog is Far More Polluted Than Acid Rain

In the Los Angeles area, measurements reveal that the fog has a pH between 2.5 and 3. Near congested areas, the fog is consistenly acidic and is laden with sulfate, nitrate, ammonium ion, lead, copper, nickel, vanadium and aldehydes. Acid fog formation involves a conversion of SO/sub 2/ and NO/sub x/ to sulfuric and nitric acids. Unlike acid rain, acid fog remains suspended in the air for hours and is a threat to human health as well as vegetation and materials. Fog forms close to the ground where concentrations of pollutants are higher than they are further aloft. Acid fog seems to be related to ground-based pollution sources, particularly power plant and automobile emissions. Samples were collected in locations far from major pollution sources and used to test the composition and acidity of normal fog. The pH values ranged from 3, near Los Angeles, to 7, near Morro Bay. Mathematical models are used to explain changes in acidity over time and to indicate a cyclical pattern.