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From: rparson@spot.Colorado.EDU (Robert Parson)
Newsgroups: sci.environment
Subject: Re: Ozone
Date: 26 Apr 1997 00:37:33 GMT

 Ozone, in very low concentrations, plays a vital role in the
 chemistry of the atmosphere. It is the major source of the OH
 radical, which is involved in almost all of the atmospheric
 oxidation processes. Without OH, and thus without ozone,
 hydrocarbons, CO, etc. would accumulate in the atmosphere.
 Natural sourced of tropospheric ozone sources include photodissociation
 of NO2, lightning, and downward transport from the stratosphere.
 The background levels in the remote troposphere are around 10 parts
 per billion. There is some evidence that they have risen somewhat over
 the last century (there are fairly good ozone measurements from
 the French Alps in the late 19th century.)

 In photochemical smog, there is a net production of ozone (ozone
 again initiates the chemistry, but the mechanisms generate more
 ozone than is consumed). Ozone concentrations in smog events
 build up to hundreds of parts per billion. This is enough to
 produce respiratory discomfort (severe for asthmatics) and
 damage to organic polymers, including rubber. (During the 1950's
 a Caltech biochemist invented the world's cheapest ozonometer,
 a set of rubber bands stretched on a wooden frame. Ozone concentrations
 were estimated from the length of time the bands took to snap.)
 Ozone itself is not an eye irritant, but peroxyacetylnitrate (PAN),
 also produced during photochemical smog events, is. Ozone and
 PAN can also produce serious plant damage.

 As usual, the dose makes the poison.


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