Cambridge, Massachusetts — Dr. Michael Y. Danilin, a Staff Scientist at Cambridge-based Atmospheric and Environmental Research, Inc. (AER), has co-authored a paper with other researchers in the United States and Scotland which argues that the continued cooling of the stratosphere expected to accompany the rise of greenhouse gases will lead to an increase in polar stratosphere clouds (PSCs) causing denitrification and, as a consequence, enhanced ozone depletion in the Arctic stratosphere.
The paper, entitled "Quantifying Denitrification and Its Effects on Ozone Recovery" by A. Tabazadeh et al. (May 25 issue of Science), examines measurements from two satellite-borne remote sensing instruments – the Microwave Limb Sounder (MLS) and the Cryogenic Limb Array Etalon Spectrometer (CLAES) - in an attempt to understand why denitrification occurs and what role it plays in enhanced ozone depletion over the Arctic in three successive winters between 1994 and 1997. Based on these data, the team of scientists concluded that an additional mechanism by which PSCs enhance Arctic ozone depletion is denitrification of the cold Arctic stratosphere. When the PSC particles are precipitated out of the stratosphere, they take with them nitric acid, a process known as "denitrification". In stratospheric ozone chemistry, nitrogen species play a very critical role. They deactivate chlorine radicals produced during PSC events, thus neutralizing them and preventing ozone depletion. The removal of nitric acid leads to denitrification, which would result in enhanced ozone depletion.
This finding relates two important global change issues – stratospheric ozone depletion and climate change. Climate scientists have shown, through model studies, that as the surface layers of the atmosphere warms with the increase of greenhouse gases (global warming), temperatures in the stratosphere cool. As the Arctic stratosphere cools with global warming, the team of scientists argues that there will be an associated increase in PSCs, resulting in an enhancement of denitrification and enhanced ozone depletion despite anticipated lower chlorine loading. The main results of this paper argue that in the future colder stratosphere, more severe denitrification could cause a delay by a decade or so of the Arctic ozone recovery despite the complete implementation of the Montreal Protocol and its Amendments.
Founded in 1977, Atmospheric and Environmental Research, Inc. is an award-winning environmental research and consulting company with demonstrated expertise in remote sensing, satellite meteorology, numerical weather prediction, climate dynamics and radiation, circulation diagnostics, atmospheric chemistry, air quality and risk assessment, planetary sciences, and systems engineering. In addition to its Cambridge, MA headquarters, AER has offices in Washington, D.C.; San Francisco and Los Angeles, CA; Hong Kong and Beijing.