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Comment by tompagenet2 | Hacker News Reader

This doesn't seem to be true: see pages 83 and 84 of the link below, suggesting around 20% of UK PM2.5 emissions come from road transport - this is not negligible.

https://assets.publishing.service.gov.uk/government/uploads/...

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That isn't refuting my statement. Road transport includes all vehicles on the road, and my statement is that trucks are by far the largest source of particulate matter on the road. The standards on trucks (and buses) are exponentially worse than passenger vehicles -- justified by the notion that they're doing something more worthwhile -- and many horribly polluting older models are grandfathered in. The average age of a passenger car on the road is much, much newer than the average age of a transport truck.

https://pubs.acs.org/doi/pdf/10.1021/acs.est.8b01914

The crux of that is that particulate pollution had a low correlation with passenger car volume, and a high correlation with trucks. Indeed, they found low utilization trucking routes had worse pollution than the busiest highway in North America (which would have been much more pronounced if the latter didn't also have significant truck volume).

Though it is worth noting that there are a number of worse sources of particulate pollution. Wood burning fires, for instance, or home gardening equipment with virtually no pollution control.

> The standards on trucks (and buses) are exponentially worse than passenger vehicles

How can one group be 'exponentially worse' than just one other group? How can you see an exponential relationship between two data points? That doesn't make any sense. You'd need to be looking at a relationship between at least three data points to say it was exponential.

You’re not wrong, but colloquially it’s common for people to use “exponentially” to mean “a lot”. Just like it’s common for people to use “massive” to mean “big” (i.e. large spatial volume).

Exponentially is often used to mean "10 times more". So if one date point is 10 times higher than a second data point, than the wording would hold colloquially.

Are you confusing with 'an order of magnitude'? Exponential is a rate of change, so you simply can't determine it on two data points. Order of magnitude is the relative change itself, so you can determine between two data points.

You are literally correct, and literally could not be more wrong (and I'm deliberately using both the correct and colloquial - but depressingly also dictionary defined - definition of the word 'literally' there).

Language evolves, and not always for the best.

No, but I agree that OOM is the better word choice. That's the great thing about the English language - whatever it means today, it won't tomorrow!

Also, to address the definition of "exponentially", I refer you to the second definition here [0]:

  -- "any positive constant raised to a power."

[0] - https://www.dictionary.com/browse/exponentially

That's not what that definition means in this content.

Think about it - you can express any change from A to B as a positive constant raised to a power. So if that's what you think it means then you're saying any change from A to B is rising 'exponentially'.

Well......Actually....

It was just an idiom as this isn't a technical discussion. I think most readers could get the idea.

If I have 5 accidents and you have 25 accidents you've had exponentially more. You don't need 3 data points, x^2 is an exponent.

Why is truck regulation so substandard? To enter the metropolitan London area (600 sq miles), HGV’s have to meet stringent pollution standards for particulates and NOx or else they pay £120 a day. Under those circumstances they aren’t a dominant source of pollution.

You’re definitely right that wood burning stoves and static plant are big sources, although location of emission is very important, someone using garden machinery intermittently on their own property or a wood burning stove out in the country is mostly polluting themselves, the same can’t be said for a freeway being driven through an urban neighbourhood.

Passenger cars in North America saw incredible advances in emissions almost entirely courtesy of California, that state spearheading demands to respond to the LA smog crisis that peaked in the 1980s. Other jurisdictions, like my home province of Ontario, just went along with the giant. It's why diesel cars are so rare, and as we know often lied (quite aside from the VW thing, every single instance where a diesel vehicle has been measured under actual use has seen emissions dramatically worse than claimed).

Big trucks, however, couldn't make the transition as quickly, and for the necessary torque still rely upon diesel. And they've gotten away with much, much worse, though again California is taking the lead and in the next few years older trucks will be banned from the roads.

Regarding the location of particulate sources, I've read that even in London, England, something like 75% of the particulate matter is from outside the city, blown in from farms and rural areas.

I was just reading about pollution sources, and you’re right that 75% comes into London from outside, compared to only 20% of NOx. Although levels of PM are double the concentration along roads compared to the background, so there is a local as well as a regional effect.

Yeah, diesel cars and trucks are a menace. I remember getting black soot in my nose in London.

I read somewhere that 50% of particulate pollution comes from brake discs/pads and tyres, meaning that electric cars will still cause air pollution. But hey, half as bad is twice as good.

The existence of regenerative breaking means that the amount of pollution from the little friction breaking still necessary should be much less.

Regenerative breaking doesn't wear pads, so only emergency breaking would count towards that 50%.

> black soot in my nose in London.

That's probably dust from the London Underground, which is mostly iron (from the rails and wheels), brake dust (ceramic) and dead skin.

There are far more diesel passenger cars in the UK than in the US. Diesel is generally far worse for particulate emissions.

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