Somewhere this morning a man with a two-stroke engine strapped to his back is out-polluting the pick-up he arrived in.<\/p>\n
That comparison comes from the state\u2019s own air quality regulator. The California Air Resources Board<\/a> (CARB) sized up the best-selling commercial leaf blower against a new light-duty passenger car and calculated that one hour on the blower produces about as much smog-forming pollution as driving that car roughly 1,100 miles. Los Angeles to Denver, give or take. Fifteen hours of freeway, matched by one worker clearing a footpath before morning tea.<\/p>\n Run the same calculation on a commercial lawn mower and the figure drops to about 300 miles, roughly LA to Las Vegas. That makes the blower, on that measure, nearly four times dirtier than the mower, out of an engine light enough to lift with one hand.<\/p>\n What the 1,100 miles is actually counting<\/p>\n Two things get lost every time this statistic goes for a walk.<\/p>\n It counts smog precursors, the reactive gases and nitrogen oxides that cook into ozone on a hot afternoon. Carbon dioxide barely enters the calculation. A blower burns a litre or so of fuel an hour and isn\u2019t going to out-warm a car on the open road. What it can do is fill a street with the raw ingredients of smog at a rate no car comes close to.<\/p>\n The second thing is the word commercial. The figure is built around the professional backpack unit, the one that comes off the landscaping ute at seven in the morning. The handheld version most people keep in the garage is smaller. It runs on exactly the same principle.<\/p>\n Why a tiny engine beats a big one<\/p>\n Someone carrying one for eight hours a day doesn\u2019t get to choose the heavier, cleaner engine, because their shoulders would give out by lunchtime. A blower has one job: move air fast, and fast air takes power. Power carried on someone\u2019s shoulders has to be light. That trade-off has pointed the industry at the two-stroke engine for about fifty years.<\/p>\n A two-stroke fires on every turn of the crankshaft instead of every second turn, so it can put out close to double the power for its weight. It also skips the valves, the camshaft and the separate oil supply. Oil goes straight into the petrol can at about fifty to one, which is why the exhaust smells the way it does.<\/p>\n The catch sits in how the cylinder empties. Incoming fuel and air shove burnt gas out through a port in the cylinder wall. But while both ports are open, a slice of that fresh mixture sails straight out with the exhaust, unburnt. Engineers call it short-circuiting. Petrol, oil and all, out the exhaust without ever having burned.<\/p>\n Then there is the equipment your car carries and the blower does not: catalytic converter, oxygen sensors, fuel injection, a computer trimming the mixture several times a second.<\/p>\n Edmunds<\/a> put that gap on a dyno in 2011, taking two blowers and a 2011 Ford F-150 SVT Raptor to an emissions lab. The two-stroke Echo backpack unit threw out 23 times the carbon monoxide of the 6,200-pound truck and close to 300 times the non-methane hydrocarbons. Engineering editor Jason Kavanagh reckoned half an hour of yard work with the two-stroke matched the hydrocarbons of a 3,900-mile drive from Texas to Alaska. One test, one blower, one truck, run by a company whose business is car reviews. Read it as a demonstration of scale rather than a settled figure.<\/p>\n One blower is a curiosity, millions are an inventory line<\/p>\n Jamie Banks and Robert McConnell, the latter an environmental engineer at the US Environmental Protection Agency, put national numbers on petrol-powered lawn and garden equipment in a paper presented to the 2015 International Emissions Inventory Conference and hosted on the EPA\u2019s own site<\/a>. Within that category, blowers, trimmers, edgers and brush cutters accounted for 43 per cent of the volatile organic compounds and around half the fine particulates. Two-stroke engines did most of that work.<\/p>\n CARB\u2019s own tally is blunter. Smog-forming emissions from small off-road engines in California already exceed those from every passenger car in the state, and the board projects they will be nearly double by 2031.<\/p>\n What regulators have done about it<\/p>\n The first real crackdown came in 2000, not 2024. The EPA\u2019s phase two standards for handheld engines, published in the Federal Register that April<\/a>, were forecast to cut hydrocarbon and nitrogen oxide emissions from trimmers, blowers and chainsaws by roughly 70 per cent by 2010. Cleaner engines went out in bigger numbers, onto more lawns.<\/p>\n