Per the most recent California Air Resources Board (CARB) Air Pollution Almanac, we can estimate the following:
If all gas powered lawn and garden equipment were converted to zero-emission appliances, it would have the same impact as:
converting almost 40% of all passenger cars to ZERO-EMISSION vehicles (in terms of reducing reactive organic gases (ROG))*
converting greater than 1 out of 4 passenger cars to ZERO-EMISSION vehicles (in terms of reducing carbon monoxide)*
* Greenhouse Agents and Smog
In addition to fuel consumption, mowers and outdoor power equipment contribute heavily to air pollution. Operating a typical (4HP) gasoline powered lawnmower for one hour produces as much smog forming hydrocarbons as driving an average care between 100 and 200 miles under average conditions. Gasoline powered string trimmers are actually more polluting than many lawn mowers. One estimate via mindfully.org states that "the 20,000,000 small engines sold in the U.S. each year contribute about one tenth of the total U.S. mobile source hydrocarbon emissions, and are the largest single contributor to these non-road emissions." These include two and four stroke gas powered leaf blowers.
A two-stroke gasoline powered leaf blower generates as much tailpipe emissions in one hour as an automobile does over 350 miles. The difference is that a car emits all that pollution over a big stretch of road, while a leaf blower deposits it all in one front or back yard.