Surprisingly the answer is a lot of pollution. Just one hour with a petrol-driven lawnmower is the equivalent of a 100 mile car trip according to the Environmental Protection Agency. This was discovered by researchers in Sweden. When you also consider that both the Environmental Protection Agency in the USA as well as the EU are looking to limit pollution from non-road engines then a lot of people are going to be wondering if they should fit a catalytic converter to their lawn mower. The best alternative is probably to install artificial grass, thus reducing pollution whilst at the same time saving yourself a lot of work.

For more information: http://www.mindfully.org/Air/Lawn-Mower-Pollution.htm