February 28, 2007
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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999
FROM VOLUME 12, NUMBER 3, MARCH 1999
Arctic Ozone Loss Due to Denitrification, A. E. Waibel et al.,Science
283 (5410), 2064-2069 (1999).
Total reactive nitrogen (all nitrogen oxides plus HNO3, ClONO2, and
HO2NO2) was measured in the Arctic vortex in February 1995 and found to
decrease by 50% between 16 and 22 km in altitude. This removal of active
nitrogen from the gas phase by sedimentation into aerosol particles (here
referred to as denitrification) is shown to substantially increase ozone
loss in the Arctic stratosphere. Model results indicate that increased
anthropogenic CO2 will decrease Arctic stratospheric
temperatures, enhancing denitrification and ozone depletion in the
stratosphere over the Arctic. This effect will offset some of the gains
made by banning CFCs in returning the polar stratospheric ozone levels to
Evidence for Bromine Monoxide in the Free Troposphere During the
Arctic Polar Sunrise, C. T. McElroy, C. A. McLinden, and J. C.
McConnell,Nature 397, 338-341 (1999).
The vertical distribution of BrO, which is autocatalytically released
from sea salt deposited on Arctic snow, was observed from high-altitude
aircraft. Significant amounts of BrO were found in the planetary boundary
layer and in the free troposphere. The BrO may have been transported there
by convection over large openings in the ice pack. Ice crystals lifted
upward by that convection provide reactive surfaces for reactions that
affect the chemistry of the free troposphere and produce ozone loss.
UV-B Damage Amplified by Transposons in Maize, V. Walbot,Nature
397, 398-399 (1999).
Increased UV-B exposure caused by stratospheric ozone depletion can
directly and immediately damage plants by a variety of mechanisms.
However, simulated field exposures of maize pollen to UV-B equivalent to a
33% ozone depletion also activated transposons that caused mutations and
created phenotypic variegation (e.g., spotting). Whereas the cytotoxicity
of a doubling of UV-B exposure would not affect agricultural output very
much and whereas damage to DNA would be repaired or would result in stable
mutations whose use could be avoided, the activation of cryptic
transposons could increase the mutation rate in maize and other organisms,
producing cycles of insertions and excisions long after activation
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