From: rparson@spot.Colorado.EDU (Robert Parson)
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.