UV-B

Most of the incoming ultraviolet (UV) solar radiation is absorbed by the stratospheric ozone layer, but UV-B (wavelengths 280-315 nm) is a component of solar radiation that reaches the Earth's surface.

Assuming similar optical properties of biomass smoke in Southeast Asia and Brazil, where UV-B and optical depth are highly correlated, optical depth measurements over Thailand and Vietnam by NASA's Terra and Aqua satellites suggest highly suppressed UVB during these avian influenza outbreaks (Mims FM III, unpublished data).

The penetration of UV-B in boreal lakes is known to increase as the concentration of (DOC) decreases.

The OSU frog study was the first to prove that UV-B is now killing organisms living at mid-latitudes.

In any case, if stratospheric ozone is declining, more UV-B sunlight should be reaching the earth's surface.

Perhaps the extra UV-B changed the substances that plants exude from their roots, Johnson speculates.

Pollen from 19 of the tested species developed significantly more slowly than pollen that wasn't exposed to UV-B radiation, the group reports in the March American Journal of Botany.

To do that, the geneticists irradiated the baby roots with a short but intense dose of UV-B, strong enough to "give us a good sunburn0 in 30 seconds," Britt says.

Many researchers had assumed that because DNA absorbs only UV-B energy, UV-B light caused the damage, says Setlow.

But at a remote research station high in the Alps, UV-B climbed by 0.5 to 1 percent per year between 1981 and 1989, report Mario Blumthaler and Walter Ambach of Austria's University of Innsbruck.

In fact, he says, scientists drew the boundary between UV-A and UV-B at what they thought was the cutoff for DNA-active wavelengths.

The concern is how much UV-B (wavelengths in the 280-to-320-nanometer spectral band) might reach earth's surface.