03 plays a central role in tropospheric chemistry. Not only is it a highly reactive and toxic species, but it absorbs both infrared and ultraviolet light, contributing to the "greenhouse effect" (see Chapter 14) and providing protection from exposure to damaging UV. In the process of absorbing in the UV, it generates electronically excited oxygen atoms that react to form OH, a ubiquitous atmospheric oxidant.
Absorption spectra of 03 are shown in Figs. 4.7 and 4.8. The strongest absorption, in the 200- to 300-nm region, is known as the Hartley bands. It is this absorption that is responsible for the so-called "actinic cutoff"
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