[at-l] pollution?

[Bob C." <ellen@clinic.net (Bob C.)]

"...  If  a  toxic  substance  is  generated  by  nature,  can  it be defined as
pollution? " asks Phil H.

This  is  complicated  question -- the answer to which depends on how you define
pollution.

Vegetation  and  wildlife  emit  a  variety  of  substances -- some of which are
healthy  to humans and some unhealthy. I think the evidence is overwhelming that
overall  trees are beneficial to human life on this planet. And animals are also
overall beneficial, even though some leave giardia cysts in their emissions.

For  example,  trees  emit  oxygen,  which is neccessary for all animal life and
hydrocarbons   that   can  contribute  to  ozone,  especially  when  mixed  with
human-produced other pollutants.

The  chemistry  is  more  complex than I can explain. But, yes, a number of tree
species  transmit  hydro-carbons,  that  contribute  to ozone -- but only in the
presence of NOx, which is mostly emitted by human sources, though I think it may
be also produced naturally also.

But  as  more  and more is learned about the complex mixture of chemicals humans
and  nature  dump  in the atmosphere, environmental scientists are learning that
the control of smog and Ozone requires significant reductions in human generated
Nitrogen oxides.

I think the general rule is obvious. Humans should not dump things into the thin
layer of atmosphere that allows life as we know it to exist on this earth.

Weary