In 1990, Congress asked EPA to look at other sources of air pollution such as nonroad mobile sources, including recreational vehicles, farm and construction equipment, boats, locomotives, and lawn and garden power equipment. Subsequently, EPA has been developing emission standards for virtually all types of nonroad equipment. These small spark-ignition engines are predominantly in lawn and garden power equipment and in some farm, construction and utility equipment. Until recently, small engines of this type were not regulated at all except in California. Small engines used in power equipment emit a variety of pollutants.
Ozone can impair human lung functions and inhibit plant growth.
In addition, NOx contributes to the production of acid rain. These engines also produce carbon monoxide, a colorless, odorless and poisonous gas which results from incomplete fuel combustion. Infants and people with heart disease or respiratory problems are especially sensitive to carbon monoxide poisoning. Compared to their unregulated counterparts, EPA estimates that engines complying with the new emission standards will emit on average more than one third less hydrocarbons. Allowable emission levels vary depending on engine size and use.