Why tires — not tailpipes — are spewing more pollution from your cars
Why tires — not tailpipes — are spewing more pollution from your cars
Planning a summer road trip? What to know about two major sources of pollution coming from your car: tires and brakes.
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edit: replies have pointed out that they probably mean "particulate pollution" throughout the piece, and are maybe being a little loose with using synonyms like "emissions" to mean the same thing. Fair enough I suppose. The whole climate change destroying the earth thing, and the well-funded denial machine that has come with it, has maybe left me a bit sensitive, but I think people should be pretty damn careful with their words when writing things like this in the Washington Post:
In California, sources other than tailpipes are the dominating source of traffic emissions. A lot of pollution comes from road dust, kicked up from cars driving along the road. In recent years, particulate emissions from brakes and tires are starting to grow as well, even outweighing those from tailpipes in some locations.
This analysis seems wrong.
In one study, Jung and his colleagues looked at car emission sources along two highways in Long Beach and Anaheim in January and February 2020. In Anaheim, they found brake and tires constituted 30 percent of PM 2.5, whereas exhaust emissions linked to gasoline and diesel constituted 19 percent. In Long Beach, brake and tires constituted 15 percent of PM 2.5 pollution, which was the same as pollution from gas and diesel.
So they are collecting air samples near highways and figuring out where it came from? Okay that seems a reasonable thing to do, but that experimental design does not seem to actually support this claim from the preceding paragraph:
In California, sources other than tailpipes are the dominating source of traffic emissions.
It must mean that tire and brakes emissions stick around longer, which is very plausible, but a different thing. It cannot be that they are dominating emissions, because that would mean they've found experimental evidence against the conservation of mass. You burn a gallon of gas every ~15 miles. That doesn't just disappear; it creates a similar amount of emissions. Whereas you lose at most a couple gallons of material on a tire over the course of its entire life, and brake pads even less so -- you probably don't go through a gallon of brake pad material in a car's lifetime. A single tank of gas is probably as much matter as all four tires will lose in their lifetime.
We're talking orders of magnitude here. This interpretation of the results seems misleading. Maybe the editorial writer here should be saying something like: Study suggests tire and brake dust lingers longer than tailpipe emissions, and could have a bigger effect on the local population.
Most of the combustion products from gas are 'clean' - water and CO2. They don't contribute to particulate air pollution.
CO and NOx are output in much smaller quantities, and are contributors to air pollution, but not to particulate air pollution.
From the tailpipe, the only real particulate matter is a very small amount of soot, and this is a small fraction of the overall combusted mass - engines are designed to minimize soot in order to increase performance and fuel efficiency.
Tires and break pads, in contrast, simply abrade into the air essentially in their entirety.
Most of the combustion products from gas are ‘clean’ - water and CO2. They don’t contribute to particulate air pollution.
Yea totally, that's why I suggested the rewrite that I did. It seems a bit nuts to exclude CO2 from the phrase:
In California, sources other than tailpipes are the dominating source of traffic emissions"
... when CO2 emissions are like ending life on earth as we know it.
A lot of things are ending life on earth as we know it. CO2 emissions are just one of them. It's like the stupid argument that plastic bags are fine because a hundred plastic bags emit less CO2 than one cotton one... But plastic bags aren't even close to being a significant element of CO2 emissions. It's a waste problem.
In this case, it's saying that particulate pollution won't magically get better by switching to EVs. The research shows that that's true.
I partially agree with you. They need a better explanation of what they were measuring for and how they came to their conclusions. Also PM2.5 may be too large to capture all the exhaust particles, a quick Google search shows some results saying 2.5 for combustion particles and others saying 2.5-1.0. PM2.5 is generally considered to be the most harmful to human health and they stay in the air longer than larger particles so maybe that's why they chose to only measure that?
But, just because the volume of gas a car uses far exceeded the volume of tire it uses does not mean that the burning of gas creates more pollutants. Theoretically, the only products of combustion are water and carbon dioxide. We know that we don't get perfect combustion, there are additives that affect things, the time in the combustion cylinder isn't ideal, and the air to gas ratios aren't always right. If we had perfect combustion water and CO2 may not be considered pollutants. Both occur naturally and have natural processes to be reused. Generally we do think of CO2 as a pollutant because we produce it in much great quantities than it naturally would be created. They exclude CO2 from their study, we know this because CO2 is much smaller than PM2.5.
It didn't really occur to me to consider an interpretation of "emissions" that excludes CO2. Had they stuck with the word "pollutant," then sure, but what they said was "emissions."
There's probably some reasonable interpretation of these findings that's productive and useful, but I think whoever wrote this is playing a bit fast and loose.