Atlantic winds transport ozone eastward.

Satellites have mapped the concentrations of ground-level ozone hovering over some of the most populous regions of North America, Europe, and Asia, Replenished by the photochemical conversion of pollutinggases, this low-lying ozone can trigger asthma attacks, cause crop damage, and possibly contribute to global warming. However, the total amount of ground-level ozone and how much of it drifts across the Earth remain poorly understood.

A new study indicates that winds flowing across the northern Atlantic Ocean "export" North American ozone to Europe. The researchers say this may prove part of a global flow of ozone in the latitudes between 30(deg)N and 60(deg)N.

Using measurements of ozone and carbon monoxide taken at three sites on Canada's Atlantic coast, the scientists also offer the first estimate of how much ozone Europeans may actually receive from across the ocean, a U.S.-Canadian research team reports in the March 5 SCIENCE.

They estimate that about 16 percent of the ozone cooked up in the lower atmosphere over the eastern United States and Canada wafts across the Atlantic in the summer, far exceeding the amount of natural stratospheric ozone likely to bleed down into the lower atmosphere over the North Atlantic in the same period. The other 84 percent of the ozone produced in the United States remains behind, eventually breaking down into simpler gases or being deposited on trees and other vegetation.

Scientists aren't sure yet what environmental mischief this ozone may cause. "But it's clear that we're making a major perturbation of the [lower atmosphere's] chemistry," says David D. Parrish of the National Oceanic and Atmospheric Administration in Boulder, Colo. "Our experience in the stratosphere with fluorocarbons tells us we should at least understand these perturbations and look in some intelligent way at what the impacts could bey

Studies of ozone export fit into a larger effort to measure ground-level ozone precisely and simulate its behavior with computers, says atmospheric chemist Jennifer A. Logan of Harvard University. Such mathematical models could specify the amount of ozone that stems from human activity, detail its global circulation, and help scientists predict the possible effects of groundlevel ozone on climate and agriculture, Logan notes.