The Pollution Continues

How bad for the environment are gas-powered leaf blowers?

Tracy A. Woodward/The Washington Post - Fall will soon be here and with it, clusters of trees with tri-color leaves. As leaves fall, some wonder whether electric leaf blowers, lawn mowers or rakes are best for the environment.

To most people, falling leaves are a beautiful sign of the changing seasons. But for many Washingtonians, the rite of fall is just another reason to have an argument. Residents of some localities have even pushed for a ban on gasoline-powered leaf blowers, which they find noisy and say are bad for the environment. Their opponents argue that banning the blowers would make leaf management arduous and prohibitively expensive. Failure to manage leaves means unattractive lawns, falling home prices — and perhaps the end of Western civilization.

By Brian Palmer, Published: September 16, 2013

I’ll leave the question of leaf blower noise to neighborhood discussion groups, but I can help resolve the environmental question: Exactly how bad for the Earth are gas-powered leaf blowers?

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How a two-stroke engine works

Much of the argument has to do with the two-stroke engine found in many of them. The two-stroke engine — so named because it completes one cycle of internal combustion in two movements of the piston — is lightweight, cheap, compact and simple, which makes it a handy motor not just for leaf blowers but also for chain saws, lawn mowers and jet skis. (There are also four-stroke leaf blowers, which use the same type of engine that powers your car and offer more complete combustion and less air pollution, but they are typically larger and more expensive.)

The two-stroke engine has developed a reputation as an environmental hazard. Because the engine lacks an independent lubrication system, fuel has to be mixed with oil. More important, about 30 percent of the fuel the engine uses fails to undergo complete combustion; as a result, the engine emits a number of air pollutants. Carbon monoxide, nitrous oxides and hydrocarbons escape from the engine in large quantities. Everyone knows the acute effects of carbon monoxide, but the other gases are equally worrisome. Both nitrous oxides and hydrocarbons contribute to smog formation. Hydrocarbons can be carcinogenic, and nitrous oxides can cause acid rain.

Cities where two-stroke engines are in particularly wide use suffer terribly from air pollution. Some of India’s urban centers, for example, are draped in heavy soot, a problem due in large part to auto-rickshaws powered by two-stroke engines. More than a decade ago, Delhi phased out tens of thousands of auto-rickshaws with two-stroke engines in favor of those with four-stroke engines that run on natural gas. This alleviated the pollution somewhat, but few cities have followed Delhi’s lead.

In leaf blowers, two-stroke engines have been shown to emit contaminants comparable to large automobiles. A 2011 test by the car experts at Edmunds showed that “a consumer-grade leaf blower emits more pollutants than a 6,200-pound 2011 Ford F-150 SVT Raptor.” The company subjected a truck, a sedan, a four-stroke and a two-stroke leaf blower to automotive emissions tests and found that under normal usage conditions — alternating the blower between high power and idle, for example — the two-stroke engine emitted nearly 299 times the hydrocarbons of the pickup truck and 93 times the hydrocarbons of the sedan. The blower emitted many times as much carbon monoxide and nitrogen oxides as well. The four-stroke engine performed significantly better than the two-stroke in most of the categories, but still far worse than the car engines.

http://www.washingtonpost.com/national/health-science/how-bad-for-the-environment-are-gas-powered-leaf-blowers/2013/09/16/8eed7b9a-18bb-11e3-a628-7e6dde8f889d_story.html