Road Dust and PM 1

[TugboatEng]

On my commute this morning there was a news story about particulate matter and premature death. They made the claim that PM causes up to 50,000 premature deaths in the state of California annually. The authors were using this to push for electrification of cars.

This seems counter-intuitive to me. Modern engines already put out very little PM. Prior to 2012 (3 years before full Tier 4 implementation) diesel PM was only 8% of PM2.5. At that time most engines would have been Tier 1 and Tier 2 which are allowed to emir 15-40x the PM of the current Tier 4 standard.

Road dust from abrasive wear as cars roll over it must make up a substantial portion of PM if combustion particulate is so low. In that case, wouldn't the additional wear from heavier electric vehicles counteract or even reverse any gains from electrification?

It also is concerning that road dust contains more harmful particulates such as metals and silica.

 

[IRstuff]

PM emission is low only when the vehicle is new, possibly. Still tons of older vehicles on the road, and poor maintenance exacerbates the problem. I probably run across one or more PM-spitting vehicles at least once a week; I tend to keep my car on recirculating air because of that, but there's probably some sort of health downside to that, as well. Most trucks seem to be less obnoxious than, say, 5-10 years ago, w.r.t. PM emission, but there are lots more trucks running around, AND they seem to not want to stay in the two rightmost lanes, these days, so on the 4-lane parts of SR91, trucks will often crowd into the 2nd from left lanes, further spreading PM clouds, if they emit.

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For three years I lived and worked within stone's throw distance of a major highway. I suffered almost continuous sinus infections. (I have only moderate preconditions of rhinitis and mild allergies - not asthma or hay fever.) All vehicles produce rubber crumb (where did we think that tear wear went to?) and one diesel pickup is probably equal to the harmful emissions of 1,000 modern cars, not to mention transport trucks. There's a reason Europe is doing an about face and banning diesels - they are a complete emissions failure in urban areas.

Then I moved to a location away from highways and dirty factories. In 20+ years I have had no infections not attributable to other causes (e.g., dunking too vigorously into a lake).

Here there are lots of chemical plant and refineries putting out aromatics (think: eventual cancer) but very little in the way of particulates. Also helping is that many aging coal plants down the Ohio Valley (our prevailing wind comes through there) have shut down.

My policy and advice is to live at least 1 mile from any major highway. If you think you are in an area with clean air, I recommend going to the far north for two weeks and see how you feel on your return (and also notice the difference in the sky colour).

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[TugboatEng]

The studies I can find about road dust pollution are funded by the tire industry and focus primarily on the "crumb rubber". Their conclusion? The rubber only makes up a small part of the particulate. Well, that's not particularly useful.

But we aren't debating the harm of PM, that is evident. I just was thinking about how to quantify the sources. Chasing after engines is probably the highest cost/benefit.

 

I've thought about that question. There must be conservation of mass, so I would start with the number of tires produced and multiply by the estimated average wear rate, which can eventually be converted to mass to obtain a decent ballpark estimate. There are probably researchers working on this math, unfunded by tire makers.
Depending on the particle size (it will be a range), the dust will settle nearer or farther away from the roads where they are produced. My suspicion is mostly nearer, but it is possible for small particles to carry very long distances. But eventually they will reach the entire planet and oceans, as we have found with microplastics.

That does not even consider the difficult to recycle carcasses and fire risk.



"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[TugboatEng]

I don't think the tires contribute significantly to the PM problem. It's ablation/abrasion of the road surface that contributes much more to the PM we breath. Moving everybody into heavier cars may make the PM worse.

 

It also must make a contribution (mass conservation), but I don't know how they compare. Both are bad.

On highways transport trucks are severe enough as to make the contribution of cars negligible, which is a big component of road taxes they pay, and why we have weigh stations.

On asphalted secondary roads and city streets, alternating cold and hot seasons are the biggest cause of degradation. Where I live, general global heating has recently resulted in annually having two or three mini winters, with devastating effects on asphalt and municipal tax burden, not to mention more and bigger potholes.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[enginesrus]

If minds were open to the happenings one may see that things are contrived. Deep factual study is needed especially nowadays.

 

As it happens I recently heard a researcher describe the findings concerning this very question. The highlights (lowlights actually) for USA were:

Light vehicle tailpipe emissions (particulates) now are exceeded by the mass of rubber crumb from tire wear.
The mass created annually is 200,000 tons.
87% ends up in rivers and streams or into the ground.
Negative effects on salmon and trout have been observed.
EVs create disproportionately more crumb than IC vehicles, due to their higher weight ~1000 lb). In fact EVs require their own specially designed tires.

So my speculation wasn’t far off the mark. A modern tire is something of a miracle in terms of design and manufacture and performance, but it contains a chemical soup of hundreds of hydrocarbons.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[rb1957]

so how will electrification (sic?) of the drive train improve the wear of the road surface ?

another day in paradise, or is paradise one day closer ?

 

[TugboatEng]

Every study I found that looked in to this hyper focused on the contribution of the tire to pollution but completely ignored the contribution of road surface abrasion. It's well known in the construction industry that asphalt dust contains harmful silica.

https://www.silica-safe.org/trainin...sure-on-Asphalt-Pavement-Milling-Machines.pdf

In terms of air pollution, I don't believe the tires to be nearly as harmful as the road surface itself.

 

More vehicle weight can’t help; it’s the reason transport trucks get weighed.

But on well constructed roads like interstates, road wear caused by light vehicles is relatively negligible. Concrete is different than asphalt obviously.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[dik]

I thought it was because of structural distress, not abrasion. Are interstates constructed using concrete, only?

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

I don't know dik, I haven't traveled all of them. Concrete is becoming more common for the Ontario 400 highways.
Concrete differs in that it breaks down structurally (if it were metal that would qualify as a form of wear), whereas asphalt suffers from several kinds of degradation. I don't think anyone has so far mentioned the leaching of hydrocarbons into the ground. It comes from the filthiest part of the refinery.
Here in Canada the hot/cold cycling is the primary cause for replacement. With global heating we have experienced several years where the winter has been split into three mini-winters, multiplying the damage (and cost). 26°C in January (2019) anywhere in Canada is an unhealthy innovation.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

so how will electrification (sic?) of the drive train improve the wear of the road surface ?

Tire wear is probably proportional to vehicle mass, other factors being equal.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[rb1957]

yes, but it's seems road wear is more significant source of particles.

another day in paradise, or is paradise one day closer ?

 

[CWB1]

Road dust is only one of several major sources of PM within urban areas. Rather than get lost in the weeds examining roads, industry, constant construction, etc I prefer to jump to the root cause - too many people and too little vegetation to filter our dirty living. Urban-dwelling "environmentalists" getting on soapboxes attacking tailpipe emissions without mentioning the effect of population density always seemed ironic to me. An even greater irony is using tailpipe emissions to advocate for electrification while many US cities' air quality has higher levels of the four regulated emissions than modern engines emit. IOW, engines have been filtering the air so electrification is counterproductive to air quality.

 

Thanks for some much needed perspective CWB1.

Roadways and vehicles are a system, as any transportation engineer could tell you. It follows that total emissions from said system would be treated in the same way.

All these issues are well researched, and a little googling might have prevented a lot of flailing around.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[TugboatEng]

One must make the distinction between an emissions and a pollutant...

 

[dik]

I think we have to look at 'anything that's left as a result of a process, that wasn't there initially' as a pollutant... If it's totally harmless and can be tolerated, then it should be allowed. Unfortunately this has never happened. Outer space is littered with 'space junk' that should never have happened. Whether it's an emission or not is not really relevant.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik