Restin256 is right, plants breathe CO2 and reject O2, contrarily to animals. However, most other chemicals, including sulfates and nitrates, do damage vegetation because they form acids when dissolved in rain water. And while CO2 may not inflict direct damage to plants, it does harm them in the long run because of the greenhouse effect, which would cause the poles to melt and cool down the Conveyor Belt, which would be what would cause the global ice age, according to the article on Indymedia.