Comment by ralferoo | Hacker News Reader

Comment by ralferoo | Hacker News Reader

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Also, one of the pictures in the article, and apparently "one of her more popular posts" is this: https://twitter.com/NicoleKelner/status/1589748415130664960

The claim is that using a two-stroke leaf blower for 30 minutes produces as many hydrocarbon emissions as driving a pick-up truck from Texas to Alaska. Clearly she has never actually thought about the logistics of this!

The shortest route I could find on Google Maps was from Dumas, TX to Metlakatla, AK at around 2500 miles. I drive a car in the UK, but that would be probably 200L or more (or 100 gallons for US folk) and even more for a truck. There's no way that ANY leaf blower gets through 3 gallons of fuel a minute! In fact, google tells me that a typical leaf blower uses 0.43 gallons per hour. So driving a truck will use approximately 500 times as much.

I'm concerned about climate change, but making completely ridiculous claims like this, even if they are pretty watercolours, isn't helping the cause - especially when it's immediately obvious that it's nonsense!

First off, kudos for putting in the effort to critically think through the implications of stats you see!

Actually, the counterintuitive truth is that two-stroke engines produce ~300-500x more PM/hydrocarbon emissions from the same amount of fuel use than a four-stroke engine, due to the fundamental nature of incomplete combustion and the oil-fuel mixture used in two stroke engines, and the efficacy of emissions controls on modern cars vs common leaf blowers. Your calculations are correct, it's just this difference is so big it seems crazy when you first learn about it. (Which is what Nicole's art is trying to communicate!) This is cited in the NYT article from the tweet you link: https://www.edmunds.com/about/press/leaf-blowers-emissions-d... , although for a more scientific source you can see https://publications.jrc.ec.europa.eu/repository/bitstream/J... .

While technically, carbureted two-stroke engines can sometimes produce less NOx than four-stroke fuel-injected counterparts for equivalent fuel use, incomplete combustion means leaf-blowers and the like have a massively outsized impact on air quality, especially for the operator. The good news is that electric systems are now cheap and lightweight enough for most applications, which is fantastic.

I think that this stat still rises to the level of being actively deceptive though.

Most people are going to take the term "Hydrocarbon emissions" to mean C02 emissions, even though it's referring to a different thing.

I'm not sure about actively deceptive. What else does it mean? Hydrocarbon emissions are what you get when you burn hydrocarbons - H2O, CO2 and CO. If it's referring to a different thing, it's not a hydrocarbon emission.

The image, and the claim within it, is actively deceptive because it's not true.

It's a little messy, and it's not clearly disambiguated what concept the artist is referring to. I agree "Hydrocarbon emissions" could reasonably mean what you get when you burn hydrocarbons, but that definition can also include literal "Hydrocarbon emissions": uncombusted or partially combusted hydrocarbon fuel being emitted out of the exhaust after ignition due to non-ideal combustion. Like you mention, this is alongside CO, as well as elemental black carbon and other trace combustion products like NOx etc...

You're right that there isn't orders of magnitude more CO2 from a two stroke, but there are orders magnitude more CO, as well as these literal "emitted hydrocarbons", which I think it what the direct claim the art intends to illustrate with either dinfinition. But the fact we're having this conversation is evidence the claim at the very least isn't clear.

That's a fair point, although I'm not sure I'd personally categorize it as "actively deceptive", I agree it could be a lot clearer about "Emissions", and empirically you're clearly right that is has some folks confused. To be charitable, like all science communication it's trying to simplify a very nuanced topic and probably could be improved. I do think the illustration of how leafblowers pollute at ~300x the rate a car does is largely true, and the GHG/environmental impact is a lot messier than just primary CO2 emissions.

(Disclaimer: I've never met or interacted with Nicole, but I know people that have, so I'm likely biased to assume good intent.)

From that article you linked to, while it's true that the figure for "NMHC" is higher (0.005g/min to 1.495g/min, yes this is almost 300x), this is just the worse case result - look at the other figures too: NOx is 0.005g/min to 0.010g/min (a doubling) and CO is 0.276g/min to 6.445g/min (about 25x). Of course, all of these figures will be dwarfed by CO2 emissions which will be roughly proportional to the amount of fuel used.

Now consider the time spent doing these activities - 30 minutes compared to 47 hours (according to Google), so multiply all those per minute figures for the truck by 100 to make a fair comparison. Now, the blower is triple the "NMHC", 2% of the NOx, 25% (EDIT: I made a mistake before) of the CO and about 0.2% of the CO2 (100 gallons vs 0.2L).

Honestly, I don't know what "NMHC" includes - as presumably it doesn't include NOx as that is called out separately, but whatever, it's just part of the emissions and so the claim that the image makes of "fewer hydrocarbon emissions" is clearly false. I'll agree that it seems to be a bad summary of the article which was "the emissions are dirtier".

EDIT: Actually, I should add that the image has done a good of raising awareness that leaf blowers are clearly pretty dirty even despite not using much fuel, so I guess it served its purpose even if after looking at the sources, I'm still not really sure by how much in actual terms, because the things I know to look out for - CO and NOx - aren't as bad as claimed, only NMHC, something I've never heard of before, and I've no idea how bad that is.

Your point may be valid if you we are talking about CO2 emissions. But if you click the source, linked as a reply to the tweet you linked:

https://www.edmunds.com/about/press/leaf-blowers-emissions-d...

You will see it is talking about other chemicals like oxides of nitrogen, carbon monoxide, and non-methane hydrocarbons.

You're assuming 1 gallon of fuel consumed by a pickup truck emits the same amount as that emitted by a 2-stroke leaf blower engine consuming 1 gallon of fuel. They definitely don't.

Odd you didn't explain how they could be different. I can't see how they can be (by much).

I link some sources in a separate comment up-thread, but the short answer is two stroke engines run orders of magnitude "dirtier" than a four stroke in a car, primarily due to incomplete combustion of fuel. (Some of this is fundamental to the physics of their operation, and some of this is they aren't subject to the same strict automotive emissions standards, so less engineering goes into reducing their emissions)

Intuitively, this is why you can sometimes taste a lawnmower running the next block over in the air, but the same isn't true for a modern car idling, even if they were consuming fuel at the same rate.

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