Surface ozone depletion

Fan, S.-M., and D. J. Jacob, Surface Ozone Depletion in Arctic Spring Sustained by Bromine Reactions on Aerosols, Nature, 359, 522-524 (1992). 

In the following sections we will discuss the main characteristics of the polar surface ozone depletion events (ODEs). 

Fan S.-M. and Jacob D. J. (1992) Surface ozone depletion in Arctic spring sustained by bromine reactions on aerosols. Nature 359, 522 -524. 

Honninger G. and Platt U. (2002) Observations of BrO and its vertical distribution during surface ozone depletion at Alert. Atoms. Environ. 36, 2481—2489. 

Miller H. L., Weaver A., Sanders R. W., Arpag K., and Solomon S. (1997) Measurements of arctic sunrise surface ozone depletion events at Kangerlussuaq, Greenland (67° N, 51°W). Tellus 49B, 496-509. 

Tarasick D. W. and Bottenheim J. W. (2002) Surface ozone depletion episodes in the Arctic and Antarctic from historical ozonesonde records. Atmos. Chem. Phys. 2, 197-205. 

An important effect of air pollution on the atmosphere is change in spectral transmission. The spectral regions of greatest concern are the ultraviolet and the visible. Changes in ultraviolet radiation have demonstrable adverse effects e.g., a decrease in the stratospheric ozone layer permits harmful UV radiation to penetrate to the surface of the earth. Excessive exposure to UV radiation results in increases in skin cancer and cataracts. The worldwide effort to reduce the release of stratospheric ozone-depleting chemicals such as chlorofluorocarbons is directed toward reducing this increased risk of skin cancer and cataracts for future generations. 

Thus we see that environmental modeling involves solving transient mass-balance equations with appropriate flow patterns and kinetics to predict the concentrations of various species versus time for specific emission patterns. The reaction chemistry and flow patterns of these systems are sufficiently complex that we must use approximate methods and use several models to try to bound the possible range of observed responses. For example, the chemical reactions consist of many homogeneous and catalytic reactions, photoassisted reactions, and adsorption and desorption on surfaces of hquids and sohds. Is global warming real [Minnesotans hope so.] How much of smog and ozone depletion are manmade [There is considerable debate on this issue.]... 

CFCs released to the atmosphere evenmally find their way up to the stratosphere where they destroy the ozone layer which protects the Earth s surface from harmful ultra-violet radiation. During the last decades, the ozone layer has been severely depleted, both over the Antarctic region where the ozone hole now appears annually, but also over the northern hemisphere. Ozone depletion up to 40% has been recorded in each of the last three years over Northern Europe. 

The presence of ionizing radiation in the upper regions of the earth s atmosphere and the realization that atmospheric chemistry can occur on the surface of ice and dust particles have lead many authors to study on the interaction of LEE with molecular solids of ozone [203], HCl [236], and halogen-containing organic compounds [176,177,195-197,199-202,205,214,217,224-234] in an effort to shed new light on the problem of ozone depletion. In a recent series of experiments, Lu and Madey [297,298] found that the and CG yields... 

Abstract Heterogeneous chemical reactions at the surface of ice and other stratospheric aerosols are now appreciated to play a critical role in atmospheric ozone depletion. A brief summary of our theoretical work on the reaction of chlorine nitrate and hydrogen chloride on ice is given to highlight the characteristics of such heterogeneous mechanisms and to emphasize the special challenges involved in the realistic theoretical treatment of such reactions. 

The discovery of the Ozone Hole in the Antarctic stratosphere has led to the realization that previously unsuspected heterogeneous chemical reactions occuring on the surface of ice and other stratospheric cloud particles play a critical role in atmospheric ozone depletion — not only in the Antarctic stratosphere,... 

This is probably the key heterogeneous reaction for Antarctic stratospheric ozone depletion, and serves as a useful focus for the discussion of the theoretical challenges that must be addressed in dealing with fairly complex chemistry in a complex environment, challenges enlivened — as will be seen below — by the evident chemical involvement of the ice surface environment. 

During the dark, polar winter the temperature drops to extremely low values, on the order of-80°C. At these temperatures, water and nitric acid form polar stratospheric clouds. Polar stratospheric clouds are important because chemical reactions in the stratosphere are catalyzed on the surface of the crystals forming these clouds. The chemical primarily responsible for ozone depletion is chlorine. Most of the chlorine in the stratosphere is contained in the compounds hydrogen chloride, HCl, or chlorine nitrate, CIONO. Hydrogen chloride and chlorine nitrate undergo a number of reactions on the surface of the crystals of polar stratospheric clouds. Two important reactions are ... 

Because of the gaseous nature of many of the important primary and secondary pollutants, the emphasis in kinetic studies of atmospheric reactions historically has been on gas-phase systems. However, it is now clear that reactions that occur in the liquid phase and on the surfaces of solids and liquids play important roles in such problems as stratospheric ozone depletion (Chapters 12 and 13), acid rain, and fogs (Chapters 7 and 8) and in the growth and properties of aerosol particles (Chapter 9). We therefore briefly discuss reaction kinetics in solution in this section and heterogeneous kinetics in Section E. 

FIGURE 6.37 (a) Surface-level 03 at Alert, Canada, and (b) filter-collected bromide (f-Br) during an ozone depletion episode (adapted from Barrie el al., 1988). 

Supporting a seawater source for the halogens is the observation by Shepson and co-workers of significant amounts of as yet unidentified photolyzable chlorine as well as bromine compounds in the spring in the Arctic (Impey et al., 1997a, 1997b). In addition, Platt and co-workers have detected both BrO and CIO at the surface during ozone depletion events (Platt and Haus-mann, 1994 Hausmann and Platt, 1994 Tuckermann et al, 1997). 

It is also clear that during periods of low surface ozone, chlorine atoms are a major reactant for hydrocarbons (e.g., Jobson et al., 1994 Solberg et al., 1996 Ariya et al., 1998). Figure 6.39, for example, shows the measured ratios of isobutane, n-butane, and propane during an ozone depletion event (Jobson et al., 1994). These particular pairs of hydrocarbons were chosen to differentiate chlorine atom chemistry from OH reactions. Thus isobutane and propane have similar rate constants for reaction with Cl but different rate constants for reaction with OH. If chlorine atoms are responsible for the loss of these organics, their ratio should remain relatively constant in the air mass, as indicated by the line marked Cl. Similarly, isobutane and n-butane have similar rate constants for removal by OH but different rate constants for reactions with... 

Sulfur 10-200% increase6 in surface area in sulfate particles Increased aerosol surface area, enhanced ozone depletion by CIO, decreased ozone depletion by NO,... 

The major focus on the effects of exhaust emissions has been on the HC1 component and its role in ozone depletion and on the A1203 particles, which could provide a surface for the heterogeneous conversion of HC1 to active forms of chlorine. It has been proposed that if the HC1 were converted to photochemically active forms relatively rapidly, a mini ozone hole could form in the flight path of the vehicle (Aftergood, 1991 McPeters et al., 1991 Karol et al., 1992). 

Leu, M.-T., Heterogeneous Reactions of N20 with H20 and HCI on Ice Surfaces Implications for Antarctic Ozone Depletion, Geophys. Res. Lett, 15, 853-854 (3988b). 

Tolbert, M. A., M. J. Rossi, and D. M. Golden, Antarctic Ozone Depletion Chemistry Reactions of N205 with H20 and HCI on Ice Surfaces, Science, 240, 1018-1021 (1988b). 

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