Comment by honk | Hacker News Reader

Comment by honk | Hacker News Reader

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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.

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.

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.)

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