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Ask the Ecologist-May 2008 |
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Written by Belle Bergner
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Wednesday, 30 April 2008 |
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Q: I heard that walking behind a lawn mower for an hour is like hanging your head behind your car tailpipe for 100 miles. Could this be true? - Nick
A: According to the California Air Resources Board (CARB), 2006 lawn mower engines contribute 93 times more smog-forming emissions than 2006 cars. Why are lawn mowers so much worse than cars? Mowers use a single-stroke spark engine with no catalytic converter. That means these engines burn a lot more oil and gas and there is virtually no filter for their emissions.
Assuming the 93 multiplier rate from CARB is correct, then running your
lawn mower for an hour is more like having your head behind a car
tailpipe for a few days – much worse than what you heard. While the
mower’s particular blend of emissions is different from cars, the major
disparity between the two motor types’ emissions is the real take-home
message: lawn mowers are really bad polluters. But if the US
Environmental Protection Agency (EPA) finalizes its proposed
regulations, lawn mowers will get a lot better after this summer. In
2007, EPA proposed to regulate small land and marine engines by
requiring catalytic converters and other improvements. EPA estimates
that by 2030, these emission reductions would prevent 450 particulate
matter-related premature deaths, approximately 500 hospitalizations,
52,000 work days lost, and other quantifiable benefits every year. The
total estimated annual benefits of this rule in 2030 are approximately
$3.4 billion. The engines and vehicles covered by EPA’s proposal are
significant sources of smogforming pollution and other health impacts.
They account for about 25 percent of mobile source hydrocarbon
emissions and 30 percent of mobile source carbon monoxide emissions.
This is a disproportionate amount when you consider that these engines
make up only 1 to 2% of the total single engines in use presently –
including cars and trucks. The answer to your question also somewhat
depends on what type of car you are driving, how well tuned it is, and
how you drive it. Manual transmission, well-tuned engines, and more
recently produced cars have fewer emissions. But the gist of the answer
to your question is that lawnmowers currently produce a heck of a lot
of bad stuff. Hopefully they’ll get better soon after EPA’s regulation
is put into law. Try a push mower this year – help make our air
cleaner, save some dough, and get some exercise while you mow. Send
your ecological inquiries to our resident ecologist at
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