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Unformatted text preview: UV light, which is usually absorbed by ozone, is no longer
sufficiently filtered from sunlight. More UV light can reach the Earth's surface. The National Research Council
predicts 10,000 additional cases of skin cancer in the U.S. for each 1% depletion in the ozone layer. This
problem will be around for a long time because currently the troposphere is a giant reservoir of CFCs.
Estimates are that there are already enough CFCs in the troposphere to cause depletion of ozone for the next 100
Currently intense efforts are underway to develop CFC substitutes. The idea is to maintain the noncorrosive
properties but make a molecule that is a little more reactive. HCFC-123 (C2 HCl 2 F 3 ), where the H represents
hydrogen, is a promising possibility. Introduction of a hydrogen atom into CFC molecules makes them more
reactive. Chemists are synthesizing a number of HCFC molecules to try as the first generation of substitutes.
The goal is to find molecules that are more easily oxidized in the troposphere, before they reach the stratosphere. Polar Ozone Holes. Since 1985 a vast hole in the ozone layer appears during the Spring months over
Antarctica. It fills in during the summer and fall, but opens again each Spring. The size of this hole has
increased every spring since then. Laboratory studies of ice particles, that mimic polar stratospheric clouds
(PSCs) that form over Antarctica during the winter, again place the blame on chlorine species from CFCs for
this dramatic loss in ozone. The concentration of the reaction intermediate chlorine monoxide in the ozone hole
is large enough to account for the ozone loss.
Chlorine can be stored in chlorine nitrate, a so-called reservoir molecule. Chlorine nitrate is an unstable
molecule that is formed when chlorine monoxide reacts with nitrogen dioxide.
ClO(g) + NO 2 (g) → ClONO 2 (g)
To explain the observed ozone depletion during the Antarctic spring, the CFC theories where adjusted to include
the reaction of chlorine nitrate with HCl on the surfaces of PSCs. These clouds contain HCl. Acting as a
heterogeneous catalysis, the...
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- Spring '08