Source: Xerces Society for Invertebrate Conservation
To be clear, I think the right thing to do with your fallen leaves is to leave them alone, to the extent that you can (Post G22-034). But if you’re going to use a leaf blower, how do gas-powered ones compare to electrics, in terms of generating C02 emissions?
Bottom line: 7-to-1. At Virginia’s current electrical generation mix, a gas-powered leaf blower produces about seven times as much C02 emissions as an electric leaf blower. I show the calculation below.
In part, that’s because the grid just keeps getting cleaner. A couple of decades ago, the difference would have been more like three-to-one. But mostly that’s because small two-stroke engines, as used on leaf blowers, are inefficient.
Note that this 7-to-1 ratio is just for C02. In terms of total air pollution, gas powered leaf blowers stack up far, far worse compared to electrics. In particular, smoky two-stroke gas engines produce huge volumes of unburned hydrocarbons, as anyone who has ever seen and smelled the exhaust from a two-stroke can attest.
To be clear, leaf blowers don’t use enough gasoline to matter, in terms of our annual C02 emissions. They are a drop in the bucket. And not that there aren’t a lot of other reasons to skip leaf blowers entirely, let alone gas-powered ones. But this is a statistic that I wanted to pin down. So here is the calculation, with citations as to source.
Background
My wife asked me a simple question today regarding gas-powered versus battery-powered leaf blowers. How do they compare in terms of C02 emissions? I did a quick back-of-the-envelope and got numbers that didn’t appear credible. So I decided to do a more formal calculation, with the metric being pounds of C02 produced per 100,000 cubic feet of air moved.
It’s already well-established that gas-powered leaf blowers produced a tremendous amount of air pollution, per amount of work performed. That owes mainly to the use of small two-stroke engines.
No shock there — these are the engines where you mix the oil with the gas, and burn that mixture to produce a smoky blue exhaust. That exhaust is every bit as dirty as it looks. You can look that up anywhere, and as far as I know there’s more-or-less zero disagreement about that. Here’s what appears to be a fairly sophisticated test (reference Edmunds).
In terms of pollutants (e.g., unburnt hydrocarbons) and such, that’s the pretty much the end of the story. Except to note that a part of the resulting air pollution is black carbon, which is increasingly being recognized as a major contributor to global warming (See Post G22-058). So, these two-stroke gas engines contribute to global warming beyond their emissions of C02 alone.
But my question was in terms of C02 emissions.
In absolute terms, obviously, the gas consumed in lawn care is a drop in the bucket, compared to the gas consumed by cars and trucks. (So, priding yourself on using an electric mower, while you drive an inefficient car, is straight-up greenwashing, in terms of impact on C02 emissions. It might ease your conscience, but in the grand scheme of things, your lawn mower is rounding error in your household carbon budget.)
That said, just exactly how do the C02 emissions compare, between gas and electric leaf blowers? My first rough cut seemed to say that gas leaf blowers produced vastly more C02, compared to electrics, than gas cars did compared to electric cars. (Which, for a Prius, is about 2.5:1. Gas miles in our Prius Prime produce about 2.5x as much C02 as do electric miles.). So I decided to do a more careful and better-documented calculation.
A virtual trip to Home Depot, and a surprise.
I went to the Home Depot website and began with the first gas-powered leaf blower that showed up. This is an ECHO gas-powered backpack leaf blower. I downloaded the manual to see what I could find out.
My first shock was in finding that this can be fitted with air pollution controls. For example, this model has a catalytic converter and a gasoline evaporation control system, at least in some areas. This, apparently, is required by law, and has been required, in at least some areas, since the mid-2010s.
Source: Manual for the ECHO backpack leaf blower referenced above.
I then looked at a similar Ryobi model, and it too has a catalytic converter as an option. That said, the owners’ manual says that it must be replaced every 50 hours.(!) Hard to find it labeled as catalytic, but it appears that the muffler assembly is a $50 part. I’m guessing the average user will not bother to replace that after 50 hours of use.
Source: Manual for the Ryobi backpack leaf blower cited above.
The important implication of this is that older comparisons — such as the 2010 testing done by Edmunds, cited above — may (or may not) be vastly out-of-date. Those older studies predate catalytic-converter-equipped units. It’s not clear to me whether all units are now equipped with catalytic converters, or whether the typical owner bothers to maintain those catalytic converters. But this does make me wonder just how much all of the often-cited literature on the dirtiness of these engines is out-of-date. I certainly see recent articles that still cite the remarkable findings of that Edmunds comparison.
It also appears that most of the advocacy articles focus on the high levels of unburned hydrocarbons. That’s where the blue-smoke-spewing two-strokes do the worst. All of them also seem to add in a huge amount of spilled gasoline, though how they could possibly know the average spill rate for the average consumer is beyond me.
Anyway, catalytic converters on two-stroke leaf blowers — that was news to me. (Though if you Google it, you can find many examples.). Maybe I’ll investigate further at some point.
For now, I’m looking for fuel consumption (which will dictate C02 output) and work produced, probably measured as cubic foot of air moved per minute.
Moving on.
After looking at a few more gas-powered leaf blowers, it’s clear that they use so little fuel that homeowners don’t care what the fuel consumption is. The issue of fuel consumption per hour, or typical run time on a tank of gas, is simply not addressed in any of the consumer literature for these devices.
You really have to dig to get it. Luckily, Stihl introduced some fuel-efficient models about a decade ago, and as part of that, they produced statistics on typical gasoline consumption per hour. These were aimed at demonstrating cost savings to professional users such as landscape maintenance companies.
With that in hand, it’s just a question of comparing some off-the-shelf plug-in electric models to a couple of efficient Stihl gas models. Here’s the calculation.
Discussion
The bottom-line figure seems completely credible to me.
For a Prius, the equivalent number would be 2.5 to 1. That’s my best estimate (presented in long-ago prior posts), based on our experience with a 2021 Prius Prime.
It’s no surprise that the ratio would be not quite 7 to 1 when comparing small two-stroke engines to electric motors. In general, engine efficient drops with size, due to proportionately larger heat losses in small engines. And two-stroke engines are designed for a good power-to-weight ratio, not for fuel efficiency. Meanwhile, electric motor efficiency — at least at this size — varies only modestly by size. And as a result, what was a 2.5 to 1 advantage for electric cars becomes a 7 to 1 advantage for electric leaf blowers.
That said, the global warming impact of these devices is almost negligible, at least in terms of C02 emissions. Note, from the table above, that you’d have to run those leaf blowers for about three hours to use up one gallon of gasoline. Compare that to the U.S. average of about 650 gallons of gasoline per licensed driver per year, and it’s obvious that leaf blowing really doesn’t much matter, in the overall U.S. carbon budget.
That said, this is just another illustration of something that I hope is becoming increasingly clear to most Americans: The future is electric. The rapid de-carbonization of the grid means that more and more frequently, the low-carbon option is going to be the electric option. Whether that’s for transportation, heating with heat pumps (Post G22-058), or for moving your leaves from place to place.
On the smugness of raking, or, TANSTAAFL
I’m sure that at least some readers have thought to themselves, “Why use a leaf blower at all? I rake my leaves, therefore I don’t use any fossil fuels to collect my leaves.”.
Well, it just ain’t that simple.
- Raking consumes energy.
- We supply that energy with fuel.
- That fuel is a highly refined substance called “food”.
- Food production and distribution consumes enormous amounts of fossil fuel.
One way or the other, everybody wants to think that there’s a free lunch. In this case, the free lunch is the illusion that if you don’t consume fossil fuels directly, then you can ignore the fact that you’re consuming them indirectly.
And I’m the guy who gets to tell you that nope, there ain’t no such thing as a free lunch. The facts are that:
- it took a lot of fossil fuels to make your lunch, and
- if more exercise means you eat a bigger lunch, then
- more exercise means you consume more fossil fuels.
The only trick is that you consume those fossil fuels indirectly, via increased food consumption, not directly, by gassing up your power tools.
I was introduced to this concept in an article entitled “Bicycling Wastes Gas?“. I can do no better than suggest that you read it.
Here’s the story of how I finally came to understand this. In my youth, for two years, I biked to work about three times a week, during the warm weather. Work, in this case, was downtown Washington DC. The round-trip distance was about 32 miles. For a guy my size, that burns about 1600 calories.
Lo and behold, I found myself eating a lot more. Conservation of energy, and all that. Those 1600 calories of daily exercise had to come from somewhere. And if my weight remained stable, they had to come from an additional 1600 calories of food.
The kicker is that, for the standard American diet, it takes about 10 fossil-fuel calories to make and deliver one edible calorie. Estimates vary, but that’s a nice round credible number. So, while 1600 calories doesn’t sound like much energy (for comparison, a gallon of gas contains about 31,000 (kilo) calories of energy in it), once you factor in how the fossil fuel energy required for one edible calorie, suddenly, you realize that your 1600 calories of typical-American-diet embodies as much fossil fuel as … roughly half-a-gallon of gasoline.
Here’s a reference that, at the end, comes to the same conclusion that I’m about to state. Bottom line: As a bicyclist, eating the average American diet, I get about 63 MPG equivalent. That is, when you divide the additional fossil fuels required, to produce the additional food I consumed, when I biked 32 miles a day, at the standard U.S. diet, by the total miles traveled, that worked out to be 63 MPGe. (Where the “e” means that it’s compared the total fossil fuel energy to the amount of energy in a gallon of gasoline.)
(You have to be careful when you do such a calculation, because exercise calories-per-hour data are always the gross calories, including your basal metabolism. Nobody cites the additional calories consumed by the exericise, over and above basal metabolism — the amount you would burn in any case. You have to derive that before doing the calculation.)
Your mileage will, of course, depend on what you eat. Potatoes embody very little fossil fuel. Beef embodies an almost unbelievably large amount. And many have pointed out that typical ovo-lacto-vegetarian diets embody about half as much fossil fuel as typical carnivorous diets (reference, Pimental, Cornell U.).
But to make this clear, assuming 10 fossil fuel calories per edible calorie, if my wife and I bike together, and maintain a stable weight, we actually consume more fossil fuel than if we drove together in a gas Prius. And me, by myself, bicycling (while eating the average American diet) consumes more fossil fuel per mile than traveling on electricity in a Prius.
In other words, if I parked my electric Prius and did all my travel by bike — while eating the standard American diet — if my travel miles were held constant, I would increase my fossil fuel consumption.
Weird, huh? And saying that inevitably makes bicycling advocates angry. Nevertheless, it’s just math. And a belief in basic physics, i.e., conservation of energy.
Arguably, the biggest fossil fuel savings from committing to using a bike rather than a car comes from total miles traveled. Because, in fact, if I have to power them myself, my total miles traveled will not remain constant. Not even when considering local transport only. A short jaunt to the hardware store by car becomes a major investment in time and effort by bike. Consequently, if my only option were biking, I’d be making a lot fewer trips to the hardware store.
What about leaf raking? With that as preamble, at my weight, this calculator says I’d burn a gross total of 481 calories per hour, raking my lawn, from which I need to net out about 135 an hour for basal metabolism (e.g., just sitting and reading). For me, then, leaf raking is a net ~350 calories per hour. Supplying an additional 350 calories, with the average American diet, requires 3500 (kilo) calories of fossil fuel energy. Or about as much as you’d get in 0.11 gallons of gas. Inverting that, by raking leaves (and replacing those calories with the average American diet), I consume gasoline-equivalents at the rate of about one gallon every nine hours.
Compare that to the gallon-every-three-hours of the smaller gas-powered leaf blower above.
Conclusion: Once you factor in the “fuel” for your leaf raking, you consume about one-third as much fossil fuel as you would using a small leaf blower. That’s per hour.
How that stacks up per cubic yard of leaves is anybody’s guess. But my guess is that, as with my example of bicycling above, your fossil fuel consumption from food-powered leaf raking is not hugely different from gas-powered leaf blowing. All due to the fossil fuels embodied in the extra food required to replace the calories burned in raking.
And, as with the bicycling example above, it’s a pretty good bet that electrically-powered leaf collection — your electric leaf blower — beats hand raking, in terms of total fossil fuel impact.
There are plenty of good reasons to rake leaves by hand. Less noise. Great exercise. Commune with nature.
And, as with bike-versus-car, if you are powering the operation with your own muscles, you’re probably going to do a lot less. You’ll likely to be motivated to move the leaves less, and maybe be motivated to #leavetheleaves. All of those are positives.
But in terms of the implications of that for fossil fuel use, that’s far from clear. Raking requires energy. That comes from food. If your weight is stable, more energy output requires more food input. And food production in the U.S. requires large amounts of fossil fuels. Bottom line is that there ain’t no such thing as a free lunch.
