If you are using a mower with a collection bag, remove the bag but check that your mower has a safety flap covering the opening where the bag was. If your mower does not have this flap, local lawn and garden stores sell retrofit kits, kits that convert regular mowers into mulching ones. Today there are numerous mulching mowers on the market. Even mowers that are not specifically designed for mulching now come with retrofit kits or simple conversions. For added environmental benefits you may also want to consider an electric mower.
Electric mowers save money on gas and oil as well as reduce air pollution.
Conventional gas powered mowers pollute as much in an hour as 40 late model cars. Users of gas lawn and garden machines also inadvertently spill an estimated 17 million gallons of fuel each year. That is more petroleum than spilled by the Exxon Valdez in the Gulf of Alaska. Most electric mowers have rechargeable batteries so there is no danger of cords. You may want to look into push, or reel, mowers.