Los Angeles TV station KTLA made this claim in an online news article today: “[California] state officials say running a gas-powered leaf blower for one hour emits the same amount of pollution as driving a 2017 Toyota Camry from Los Angeles to Denver, a distance of about 1,100 miles (1,770 kilometers).”
So can we check this claim? We are comparing a small single-cylinder 2-stroke internal combustion engine running for an hour to a (probably) 4 cylinder 4-stroke engine running for about 18 hours (1100 miles @ 60MPH average). How much pollution would each generate?
We don’t know what pollutants they are talking about, so we’ll have to guess. None are diesel, so there is little particulate matter, just gases.
Well, for starters, we can find the fuel usage. The car will get, what, maybe 40 MPG? So that trip would take about 25 gallons of gasoline. I’m not familiar with gasoline leaf-blowers-- How much would one burn in an hour?
From there, yes, we do need to know what pollutants they’re talking about. If it’s carbon dioxide, then the amount is almost directly proportional to the amount of fuel burned, and there’s almost nothing you can do about that. But I suspect that they’re looking more at unburnt fuel, nitrogen oxides, and ozone, and there’s wide variation in how much of those different engines produce. Cars not only have the luxury of larger size (and thus room for more pollution-control measures), but car makers have been working on decreasing pollution levels for decades, while there’s been very little similar effort for yard appliances.
Fuel (evaporative and unburnt) and exhaust emissions consist of hydrocarbons (HC), oxides of nitrogen (NOx), carbon monoxide (CO), and fine particulate matter (PM). Emissions from gas powered leaf blowers are substantial. The amount of CO (carbon monoxide) emitted from a typical backpack leaf blower for just 1 hour is equal to CO coming from the tailpipe of a current year automobile operating for over 8 hours. For the other pollutants, the amounts are even greater.
More information is available in the March 2016 document " Nonroad Spark-Ignition Engines 19 Kilowatts and Below: Exhaust Emission Standards " available through the EPA link in the right hand column.
They are as loud as a Table Saw in many cases.
The Dust Emissions very high.
Directly from the EPA is this PDF from 2015:
Go to Page 8 of the report, and the gasoline-powered lawn and garden equipment is a shockingly high percentage of air pollution.
Are two-stroke engines worse for CO and unburnt hydrocarbons? Most weed trimmers and leaf blowers are two-stroke (as was the small snowblower I used to own).
Related OG Dope article on two-stroke vs car, which covers @Marvin_the_Martian 's question as well as general info pertinent to the topic.
Short version is that the scooter (and presumably the leaf blower) have massively higher allowances for most pollutants
Cars and light-duty trucks (including SUVs). Maximum CO emissions: 7.5 pounds per thousand miles. Unburned hydrocarbons: 0.154 pounds. NOx: 0.154 pounds.
Scooters and small motorcycles. Maximum CO: 42.57 pounds. Unburned hydrocarbons: 3.55 pounds. NOx: no limit.
But carbon dioxide production (thus carbon footprint) is much worse for cars as it is a factor of mileage. So they all suck. This is a 2009 article, so the newer vehicles, with better performance will certainly mitigate issues - but I suspect they’re looking at something like NOx which isn’t/wasn’t regulated for the two-stroke scooter at all.
Is there any way to calculate, using generous error bars, the pollution (whatever that is) difference between the two sources as initially presented? I’d really like to know if the KTLA claim quoted in post #1 is true, mostly true, or wildly false.
I’m not asking which is better for the environment. That question would have to take into account any pollution indirectly caused by device manufacture and eventually, disposal, as well as many other factors.
So, digging through the website for the California Air Resources board, they have the following PDF which seems use the language cited in the report from the OP
But it doesn’t specify the actual pollutants being considered. Just that up until now, CA has mandated lower and lower emissions for motor vehicles but not equivalent pollution reduction in ‘Small Off Road Engines’ (19 kw or less). They just include ‘smog forming emissions’ - not specific pollutants such as were laid out in the OG post.
They have nearly the same claims and graphics going back at least 4 years now, but not with detailed numbers.
Now a deep dig on the same website found the following PDF from 2020 which seems to at least track nitrous oxides as well as other smog forming hydrocarbons
But again is an analysis of trends and tracking, rather that detailed what pollutants per hour of normal usage.
But after nearly an hour of digging, I found this bad boy -
Which from 2012 seems to be the current exhaust emission standards - a small chunk says that post 2008 production of spark-ignition engines allows for no more than 10 grams per kilowatt hour of hydrocarbons and nitrous oxides and 549 of carbon monoxide in devices >80 cc - <225 cc and 8/549 for >= 225cc. Some exceptions apply, but this seems to be the baseline. (from page 13 of 53, you’re welcome)
So we have a baseline of what is currently allowed, but it’s comparing kilowatt hour vs miles driven in cars, so not fully helpful, and I’ve spend waaaaay too much time digging through the website.
Heck, other sources point out that different analysis gives different numbers, in this 2018 article (which is from a natural energy website so absolutely going to have bias) mentions several analysis -
Another estimate is that every gallon of gasoline burned by lawnmowers emits 20 pounds of CO2. According to the EPA, one gas lawn mower emits 89 pounds of CO2 and 34 pounds of other pollutants per year. According to a Swedish study, using a mower for one hour has the same carbon footprint as a 100-mile car trip.
Lawn mowers are not the only cause of greenhouse gases produced in lawn care. According to statistics based on US Census data and the Simmons National CO2 Consumer Survey, 115.5 million Americans own leaf blowers. It has been estimated that thirty minutes of their use produces the same amount of hydrocarbon emissions as driving a car seventy-seven hundred miles at a speed of thirty miles per hour.
Besides producing greenhouse gases, mowing our lawns produces other types of pollution. The EPA estimates that hour-for-hour, gasoline powered lawn mowers produce 11 times as much pollution as a new car. According to the EPA, each gas-powered lawn mower produces as much air pollution as 43 new automobiles driven 12,000 per year – lawn care produces 13 billion pounds of toxic pollutants per year.
Of course, sadly there were no links to the EPA in the article, and having gone crazy with the CA one, figured I’d leave it to someone else. But there you go, it depends on who you trust - Sweden would say 1 hr = 100 miles driven, CA says 1 hr = 300 miles. Even with broad strokes I don’t think we can evaluate fully with this much variance. Still, when you consider the other ecological impacts of American love of lawns, I agree that they’re a terrible waste in nitrogen run off, overuse of water, poor use of land, and the lawnmower and leafblowers (which apparently are several times worse than mowers) are just the icing on the cake.
But back to the OP - the SORE document I cited earlier says 1 hour = 300 miles, NOT 1100. But they could be considering a riding lawn mower or higher draw - none of which is clear from the original cite.
For a sheer grams-for-grams comparison, you’d need to know the power level for the small engine.
Let’s take a lawn mower. I’ve got a battery-powered mower these days, but my previous model had a 4-horsepower engine (3 kW). To be fair, let’s assume it doesn’t run at full rated power all the time; let’s assume an average of 2.25 kW during normal operation. So if I operate it for an hour, that’s 2.25 kW-hours. Based on the numbers in your post, that means in one hour my old mower was allowed to put out:
HC+NOx: 225 grams
CO: 1235.25 grams
For cars (“light duty vehicles”), I found this table:
Take a late-model car, say, 2018. estimated emissions are as follows:
HC+NOx: 0.584 grams per mile
CO: 4.646 grams per mile
So if we compare HC+NOx, then operating my gas mower for an hour is equivalent to driving a MY2018 car about 385 miles. Comparing CO, it’s the equivalent of 265 miles. If you want to come up with some kind of crude average, you might say operating a mower for an hour is like driving a car 300 miles.
That’s a lot less than the 1100 miles described in the OP. However, the table I linked to is for average emissions, and includes all modes of operation: cold start (summer+winter), idle, city driving, and highway driving. The OP’s scenario described driving a Camry from LA to Denver. That’s all highway miles, with maybe two cold starts. The total emissions for that journey will be a lot lower than the emissions for the aforementioned “average” driving. It’s entirely plausible that running a mower for an hour is like driving a car from LA to Denver, at least on the basis of noxious pollutants (HC, CO, NOx).
For CO2, it’s a different story. As noted, CO2 output scales almost perfectly with fuel consumption. For a 2018 Camry with a V6 engine, the highway fuel economy is 33 MPG. Not sure about my lawn mower, but I think in an hour it used to burn maybe a pint of gas. In other words, running my mower for an is equivalent to driving a Camry about 4 miles down the highway.
@Musicat asked about a gas-powered leaf blower though, not a lawn mower. The former tends to have lower power ratings than the latter, but not by a lot. This backpack leaf blower is rated for 2.8 ps, or 2.06 kilowatts
While less than my mower, a leaf blower tends to run all-or-nothing, so in an hour’s time you’d expect an honest 2 kw-hours of work out of it - not much less than the 2.25 kw-hours I estimated for my mower. I’m still confident that this compares fairly with an 1100-mile highway journey by a late-model mid-sized sedan.
@Musicat 's claim was that two different machines designed for two different jobs running for two wildly different periods of time gives us very similar results.
Absolutely, at least as far as unburnt hydrocarbons are concerned. The big issue is that two-stroke engines have a combined compression/exhaust stroke (the piston’s up-stroke), and a bit of the unburnt fuel/oil/air can go out with the exhaust, and on top of that, they generally work as total-loss oil systems, in that the oil is mixed in with the fuel and is ideally burnt completely with each stroke, which is more polluting than just gas, and some is always not quite burnt and goes out as aerosols/droplets with the exhaust.
I don’t know about CO emissions, but I suspect that it’s the same there, mostly due to lack of control and emissions equipment. On a car with a four-stroke engine, you have a couple of things working to minimize CO. First, the air/fuel ratio is constantly being monitored and adjusted by the engine sensors, including the oxygen sensors and the intake air sensors (MAFs and the like). That constant adjustment keeps it right where it needs to be to maximize power and minimize emissions. Second, the catalytic converter is fantastic at converting CO to CO2, and reduces those emissions dramatically- from something like 30,000 ppm to less than 1000 ppm.
Two strokes have none of that- there isn’t any automatic adjustment to ensure that the right air/fuel ratio is being achieved, and there aren’t catalytic converters either.
Put another way, a weedeater/leafblower/whatever, may have a $15 carburetor regulating the fuel/air mixture, while a car has a multi-thousand dollar suite of sensors and engine management computers to manage its fuel/air mixture and emissions. So it makes sense that the small engines would have vastly worse emissions as a result.
I’d think that it would almost have to be calculated as the various emissions per unit of fuel, per engine.
I mean it stands to reason that a gallon of fuel run through a leaf blower is going to produce FAR more harmful emissions overall than a gallon of the same fuel run through a modern car in good condition.
The CO2 should be roughly the same, unless the 2 cycle is producing more of something ELSE because of incomplete combustion, etc… as there’s only so many carbon atoms per gallon to be converted into CO2 in the first place. But other stuff like particulates, unburned hydrocarbons, CO, etc… are likely considerably higher for the 2 cycle engine.
The problem with the OP statement about one hour of a leaf blower vs. 1100 miles of a Toyota Camry is so vague as to be nearly meaningless. “Pollution” is not well defined here- I wouldn’t be at all surprised if a leaf blower puts out more unburned hydrocarbons or carbon monoxide than a modern car traveling 1100 miles; things like EGR, catalytic converters, stoichiometric mixtures controlled by sensors and computers, etc… make modern cars emit absolutely tiny amounts of that stuff per gallon.
Well, the Mythbusters compared cars and motorcycles in the episode “Bikes and Bazookas” from the 2011 season, episode 12. They found that motorcycles were worse in pretty much every respect except for fuel efficiency and thus CO2 emissions (however newer high-performance motorcycles can have pretty lousy fuel efficiency that can be worse than a car). Nonetheless, hydrocarbons, nitrogen oxides, and carbon monoxide were all worse for the motorcycles, in most cases by an order of magnitude. I don’t recall if the newest motorcycle had a catalytic converter or not, but those are still not ubiquitous, let alone for lawn equipment which would fare even worse than a motorcycle.
This is a 2009 article, so the newer vehicles, with better performance will certainly mitigate issues - but I suspect they’re looking at something like NOx which isn’t/wasn’t regulated for the two-stroke scooter at all.