Many people are unaware of the pollution caused by the common mower. The truth is many mowers are still in the stone age. There has been very little regulation when it comes the small engines. This oversight has cost us dearly. One mower running for an hour produces as much CO2 and chemical emissions as 40 cars on the road. A bit disturbing, I will agree.
This is a great site that lays out the harmful effects of inefficient mowers on the environment.