Want to directly prevent 26 pounds of carbon pollution every time you mow your lawn? Hire Uncle Onion instead of using gas!

 

Simply put, this statement is claiming an electric mower produces about 26 fewer pounds of carbon per hour than a gas lawn mower. The calculation is below, but it works out that a gas mower produces 26.55 pounds of carbon every hour, and an electric mower produces about .56 pounds of carbon every hour. An hourly savings of about 26 pounds of carbon.

 

Background:

I have found sources that say operating a mower for one hour produces the same amount of air pollution as driving a car "x" miles. I say "x" miles because some sources say 300 miles, some say 350 miles, and some say 100 miles. As you can see in the sources listed below, California Air Resources Board (CARB) says 1 hour of lawn mower use is equal to driving a car 300 miles. They attribute this source to EPA, but I can't find anywhere where the EPA says that. I did, however, find on EPA's website some information about car emissions, so I calculated vehicle emissions over 300 miles using EPA data on vehicle emissions, and came up with 267 pounds of CO2. Because of catalytic converters and other emissions systems on new cars, this isn't the amount of CO2 that actually leaves the tailpipe. Therefore, a lawn mower does not produce 267 pounds of CO2 every hour, and this is not an apples to apples comparison without knowing how much CO2 is scrubbed by the car's emissions system. Keep reading, this rabbit hole only gets deeper. 

 

From two sources, EPA and CARB (links below), and using the EPA's assumption the car gets 22 mpg, I used the following formula to come to the 267 pounds an hour conclusion:

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To find the amount of CO2 generated by a car driving 300 miles at 22 MPGs, I used this formula:

 

300 miles / 22 mpg = 13.63 gallons of gas burned

13.63 gallons x 19.6 pounds of CO2 per gallon of gas = 267.15 pounds of CO2

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267 pounds of CO2 emissions in a 300 mile car ride seem reasonable to me. But 267 pounds in one hour of using a gas lawn mower does not seem likely.  

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To come up with the 26 pounds of emissions published on our website, I found this website that has a formula for calculating your lawn mower's carbon emissions. The math is for an entire year, but by changing the number of mowings per year to 1, you can figure out the hourly emissions of any mower with this formula. Note this formula calculates carbon, not just CO2, so the multiplier is different than the EPA calculation that was figuring for CO2. Here is the math with their formula:

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Electric lawn mower: electricity used per year = (hours mowing the lawn) x (number of times you mow per year) x (lawn mower power rating in kW). Your carbon footprint is calculated like this: Footprint = (kWh) x (1 pound carbon per kWh). Here's the formula on my ZTR for one hour of use (in theory):

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Electricity used = (1 hour mowing the lawn) x (1 mowing) x (.56 kW) 

Electricity used = .56 kWh electricity per hour

Footprint  = .56 kWh x 1 pound of carbon per kWh

Footprint = .56 pounds of carbon emissions per hour

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Note: Our batteries are 56 volt, 10 Ah (560 watts, or .56 kWh). We keep 6 batteries in our ZTR, but it still only uses .56 kWh, not .56 kWh x 6. This is because it only needs .56 kWh to run. Adding extra batteries increases the run time, not the consumption of electricity. Think of it as a 6 gallon fuel tank, and each battery is 1 gallon of fuel. The mower can run on 1 battery, or 1 gallon of fuel, but it'll run longer if we fill it up with 6 batteries, or 6 gallons of fuel. The kWh is equivalent to the fuel mileage of a combustion engine, and just like with a combustion engine, it doesn't change based on the amount of fuel in the tank.  

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Gas lawn mower: Gas used in 1 year = (hours mowing the lawn) x (number of times you mow per year) x (gas used per hour). Carbon footprint is calculated by: Footprint = (gas used) x (17.7 pounds of carbon per gallon). Here's the formula for a gas mower's carbon emissions over 1 hour of use at 1.5 gallons of gas burned per hour (seems to be a typical burn rate for most lawn mowers):

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Gas used = (1 hour mowing) x (1 time mowing per year) x (1.5 gallons of gas per hour)

Gas used = 1.5 gallons

Footprint = (1.5 gallons of gas used) x (17.7 pounds of carbon per gallon)

Footprint = 26.55 pounds of carbon emitted per hour

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These formulas are theoretical since we aren't measuring the actual electricity or gas used or considering where the electricity is produced. For example, if all our electricity was produced by solar, our carbon emissions would be 0 (yes, I know about embodied carbon, but that's a different topic). Our electricity is produced with more nuclear and less coal and gas than the national average, so I'm sure our actual carbon emissions are lower than 1 pound per kWh, as used in the formula. The numbers are solid enough to use as a comparison tool without needing the other information. The pounds of carbon per gallon of gasoline are even less than the sources below show (closer to 20 pounds per gallon). 

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Sources:

According to California Air Resources Board (CARB), 1 hour of gas lawn mower use = the same amount of air pollution as driving a car 300 miles. I've seen this statistic credited to EPA in other places on the web, but I can't find anywhere where the EPA says it. 

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According to US EPA, every gallon of gas burned produces about 8,887 grams (19.6 pounds) of CO2. 

 

If you're like me and you are wondering how 26.55 pounds of carbon can come from burning 1 to 2 gallons of gasoline, here and here is some information that helps explain it. 

More reading: 

Until 2012, small gas engines, such as those on lawn mowers, have gone largely unregulated as far as emissions are concerned. In 2012, regulations were finally put in place that were supposed to cut emissions across the board from small engines by up to 70%. The evidence shows that even after 2012 and even though electric lawn equipment are gaining a larger share of the market, greenhouse gas emission rates from small engines have been largely unchanged, and in some cases have continued to increase, albeit slightly. Virtually all of the statistics referenced on UncleOnionsLawn.com are from studies performed between 1990 to 2012. I haven't been able to find many studies on small engine emissions after about 2002. This website from CARB has good information about pre and post 2012 emissions information. You'll see that such little has changed since 2012, that the studies and statistics from before the 2012 regulations are still relevant.  

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I've seen the EPA credited as saying a lawn mower emits the same amount of CO2 as driving a new car 300 miles, 350 miles, or even driving 43 cars 12,000 miles a year (sources on this latter information further below in another section). But I haven't seen anyone come out and say, "A gas lawn mower produces "x" amount of carbon (or carbon dioxide) in an hour of operation. This article comes the closest, but I can't find a credible source for the "fact" that states, "One gas mower spews 87 lbs. of the greenhouse gas CO2... every year." 87 pounds sounds incredibly low for a yearly emission rate, when that same article quotes EPA saying a gas lawn mower emits as much air pollution in one hour as 43 new cars driven 12,000 miles. I've contacted them about their source for this information, but have not heard back.

 

According to CARB, commercial and residential lawn equipment emitted 80 tons of hydrocarbons and NOx EVERY DAY statewide in 2020.