The dust stirred up by drought conditions may sometimes help neutralize acid rain, but it can also form other harmful chemical products in the atmosphere, scientists reported Wednesday.

Dale Gillette of the National Oceanic and Atmospheric Administration said studies have found that dry, windy drought conditions - like those that affected large regions of the United States last summer - increase the amount of dust in the atmosphere.In findings presented to the American Geophysical Union's fall meeting, Gillette said the action of the dust on atmospheric chemistry appears to depend on the source of the wind-blown dirt.

Dust from roads usually is high in calcium and low in clays, and if such dust rises high enough in the atmosphere its alkaline content can neutralize the precursors of acid rain, said Gillette, who works at NOAA's Air Resources Lab in Boulder, Colo.

However, a different scenario apparently takes place with dust blown off fields. Gillette said such dust is lower in alkalines and often contains clays that can be dissolved by acidic compounds in the atmosphere, releasing soluable aluminum and other toxic metals.

Acid rain is highly acidic precipitation produced when emissions high in sulfur and nitrogen, such as those from coal-burning power plants, combine with water vapor in the air. Environmentalists have blaimed such rain for poor tree growth and acidic lakes in which aquatic life finds it difficult to survive.

In their study, Gillette and colleagues from Florida State University and the Cooperative Institute for Research in Environmental Sciences analyzed atmospheric dust collected at nine sites in the northeastern United States. The researchers found all the samples contained aluminum and sulfur.

Gillette said concentrations of clay particles in the air near the Adirondack Mountains were high enough to account for the levels of dissolved aluminum and sulfate in local lakes.

As for the West, the NOAA researcher said he found dust-related toxic chemicals were even more prevalent in the air, and claimed their levels were comparable to sulfur dioxide emissions from major air pollution sources.