Ozone Depletion, Chlorine, and Volcanic Eruptions 2-D Chemical Transport Model
Depletion of the ozone layer by chlorine radicals resulting from atmospheric degradation of anthropogenic chlorine-based compounds such as CFCs (chlorofluorocarbons) is a well-recognized and serious phenomenon. The AER 2-dimensional chemical transport model (CTM), developed by Dr. Nien Dak Sze, Dr. Malcolm Ko, and Debra Weisenstein, was instrumental in confirming the relationship between CFCs and global ozone depletion and helped shape policies reducing and banning the use of CFCs.
The AER 2-D CTM is a model that predicts how the ozone layer will behave through time under a variety of conditions and assumptions. It calculates concentrations of 80 chemical species in the atmosphere at 969 grid points, covering the globe from the surface to 60 km altitude. It also calculates the distribution of sulfuric acid aerosols in 40 size bins resulting from surface emissions of sulfur-bearing gases and explosive volcanic eruptions that penetrate the stratospehre. Different scenarios can be explored through model calculations, such as future emission rates of chlorine- and bromine-compounds, future concentrations of methane, changes in stratospheric temperature, or hypothesized emission of pollutants from aircraft or rockets. Results of such studies have been published in global ozone assessment reports published by the World Meteorological Organization and the Intergovernmental Panel on Climate Change.
Volcanic eruptions that penetrate the stratosphere, a rare (once or twice a decade) though natural phenomenon, lead to stratospheric ozone depletion through heterogeneous reactions (ie. reactions between gas phase molecules and solid/liquid surfaces) on aerosol surfaces which change the balance among nitrogen, chlorine, and hydrogen radicals. The most important reaction in these high-aerosol conditions converts dinitrogen pentoxide (N2O5), a short-lived reactive compound, to nitric acid (HNO3), a longer-lived less reactive compound. With a greater fraction of nitrogen atoms as HNO3, there are fewer nitrogen atoms to react with chlorine atoms, and therefore more free reactive chlorine available to destroy ozone. The impact of volcanoes on ozone depends on the concentration of anthropogenic chlorine in the stratosphere. In the case with lower chlorine shown here, the resulting ozone depletion is much less. If there were no man-made chlorine in the stratosphere, explosive volcanic eruptions would lead to increases in ozone.
To learn more about the Ozone Layer http://www.epa.gov/ozone/
http://www.nas.nasa.gov/About/Education/Ozone/
Nien Dak Sze, Ph.D.
Dr. Sze recognized in 1977 the opportunity to assist industry in the accessing the impact and implications of the then new Environmental Protection Agency regulations. Since then AER has successfully promoted the advancement of the scientific understanding of the atmospheric science, climate and weather, remote sensing, ocean sciences and planetary sciences and applying that knowledge to solve real world problems, working with businesses and policymakers. In his career Dr. Sze has served on many US and international advisory boards including serving as a Science and Technical Adviser for the National Environmental Protection Agency of the Peoples Republic of China, and Chief Scientist for the US-PRC Atmospheric Chemistry Modeling Program under the Bilateral US-PRC Protocol on Atmospheric Science & Technology. He has served on the Executive Committee of the NASA Global Tropospheric Experiment (GTE) which conceptualized, planned and coordinated with HKRO, HKP and HKCAD for two major Airborne Campaigns over Hong Kong and Western Pacific in 1991 & 1994, and as a member of the theory team of the NASA Airborne Antarctic Ozone Experiment, which provided on-site modeling support to the field campaign that obtained the unprecedented data set relating the Antarctic Ozone Hole to CFCs’ emission; the findings helped solidify the Landmark International Ozone Treaty---the Montreal Protocol. Dr. Sze has also served as consultant to a number of Fortune 100 companies in US and Overseas.