I thought the concept was opposite to that: If you upgrade or build to
better than the declared standard, the amount you under-polute gives you
credits which you can sell to the over-poluters.

You're right - I had it backwards. But the theory is the same - reduce
total pollution by doing so where it is most cost-effective to do so.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.