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Comparative assessment of the environmental performance of small engines
Department of the Environment and Water Resources, February 2007
This report sets out the results of a project to compare and benchmark emissions from small petrol engines (less than 19 kilowatts) that are used to power outdoor garden equipment and were available for sale in Australia during 2006. The equipment powered by these small engines are used in lawnmowers, brushcutters, hedge trimmers and the like.
These engines emit volatile organic compounds (VOCs) and oxides of nitrogen (NOx) which contribute to ozone (photochemical smog) formation in summer. They also emit particles, carbon monoxide (CO) and a range of air toxics such as benzene.
Sydney’s Greater Metropolitan Region (GMR) annually records exceedances of the National Environment Protection (Ambient Air Quality) Measure (Air NEPM) ozone standards. The other jurisdictions meet or are close to meeting the current ozone standards.
The Air NEPM standards are being reviewed and based on current human health evidence the argument appears to be strengthening for tighter ozone standards. Should a stricter standard or an eight-hour standard consistent with international standards/guidelines be adopted, achievability of Air NEPM ozone standards or goals could become an issue for some of the other major urban airsheds.
The United States, California, Canada and Europe regulate emissions from outdoor equipment - the USA has had these in place since 1997. There are no Australian regulations or standards that limit air pollutant emissions from engines used in outdoor garden equipment however as the majority of equipment sold in Australia is imported some do comply with emission standards applicable to the country of origin.
Small engines are not as advanced in environmental terms as motor vehicle engines. As a result even the better-performing small engines emit far greater quantities of pollutants per hour than typical modern car engines. For example the US Environmental Protection Agency (USEPA) 2002 limit for a typical 4 kilowatt (kW) lawnmower motor is about 66 grams (g) of regulated pollutants per hour of operation. A typical 0.8kW brushcutter sold new in 2002 emitted about 160grams of pollutants per hour - reducing to 40grams per hour if bought new in 2006. The equivalent limit for cars under Australian Design Rule 79 is about 16g per hour. In other words, one hour of operation of a brushcutter that meets USEPA 2002 limits produces the same pollution as ten cars, operated over a similar time. These comparisons are subject to differences in test methods but they do provide an indication of the disproportionate amount of pollution emitted by small engines.
Engines that do not comply with current USEPA requirements are likely to emit several times the amount of pollution calculated in the above example. Therefore the worst performing engines are likely to emit more than ten times the emissions of the best performers.
Based on estimates made using the National Pollutant Inventory database, engines used in lawn mowers contribute approximately 4% on average to VOC emissions from anthropogenic sources in major airsheds in Australia when public open space lawn mowing is included. This is likely to rise to around 11 % in the warmer spring and autumn weekends which is when lawns and other vegetation grows faster and when gardening is more popular. The NPI does not take into account emissions from other types of powered outdoor equipment.