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.