Emissions from commercial and domestic sources (domestic wood heaters are considered separately) exert pressure on local air quality and on airshed quality. Domestic sources, for example, can affect photochemical smog by releasing VOCs.
In recent years, much focus has been on the emissions from nonroad spark-ignition engines and equipment, such as conventional 2-stroke engines used in the gardening sector (e.g. lawn mowers, outdoor handheld equipment), the marine sector (e.g. outboard engines, personal watercraft), and other equipment such as small generators. Air pollutants emitted from these engines include nitrogen oxides, VOCs, carbon monoxide, air toxins (including benzene and polycyclic aromatic hydrocarbons) and PM. These engines put pressure on urban air quality because they are high polluters relative to their engine size and use. On an individual engine basis, even the better-performing nonroad engines emit disproportionately high levels of air pollutants compared with typical modern car engines. Nonroad spark-ignition engines and equipment are responsible for two-thirds of the nonroad emissions of VOCs in Australia (EPHC 2010b).