I thought I might offer some points. I'm a biologist and work mainly in water
quality. We have run experiments to see what effect wealthy areas and poor
areas have. In the wealthy areas we tested, the cars were mostly newer and on
the flip side, there were mainly older cars in less affluent areas. We noted
MUCH more in the way of spilled oil/radiator fluid/etc in those less affluent
areas as well. We tested for first flush which is that water that first gets
washed out upon the first part of a good rain. I can tell you that the feeling
is that most older cars (not necessarily those who read this...but maybe ;-))
have the leaks and such that you'd expect with age and poor upkeep. Also,
there is less effort to fix less than severe leaks in poorer areas. We did
find a correlation of high pollutant runoff in the poorer areas. This ranged
from metals to motor oil, etc. Now before those of you who are well off start
to feel superior, there was a correlation to the affluent areas that may not
make ya feel real good either. The affluent areas had high amounts of
fertilizers, pesticides and herbicideswhile those pollutants were low (if
present a t all) in the poorer areas. (that last part has nothing to do with
autos...just wanted to be fair). Now, true...those who have their cars in good
order do not cause the excess pollutant load. But, there is validity to the
points made about older cars in general. There are a good many air quality
experiments in literature that also bear witness to this. The moral? Good
upkeep lessens the argument considerably. But, this is probably preaching to
the choir.