Air-Purifying Road Surface Eats 45% of NOx Pollution | Hacker News Reader

Air-Purifying Road Surface Eats 45% of NOx Pollution

sciencedaily.com

44 pointsMikeCapone29 comments

There are two problems with this that I can see right off the bat.

1) There is already a large problem with excess nitrogen runoff due to fertilizers, which is causing massive algae blooms in oceans, destroying aquatic life. This would have a similar effect from my understanding

2) Titanium Dioxide is kinda nasty to manufacture, in that it uses large quantities of chlorine. Also, it has been classified as a potential carcinogen.

With those being said, as long as the net effect is a reduction in harmful pollutants or carcinogens, rather than an increase, it's a win-win. It's just a bit difficult to understand that without probably rolling it out widespread.

Indeed, it's not without problems. The question is, are those problems smaller than the problems we have now? Or is there another solution that has fewer downsides.

I'm curious to know if NOx end up breaking down to nitrates after a while anyway? It might not actually add to the problem.

That's a good point, and a bit of reading (not research, so take it with a grain of salt) says that atmospheric NOx breaksdown into nitrate particles + some nasties.

re 2: ain't it wonderful that it's in nearly every white-paste-product out there? Toothpaste and sun screens in particular.

I trust my luck with the sun rather than sunscreen, I love the salt stick deodorant (works great, reapply as needed), and there is no better toothpaste than flouride free Toms of Maine :)

Are you just lucky enough to be un-sun-burnable? Or are you doing that hippie thing where you say 'ultraviolet radiation is natural! It can't be bad for me!'?

Also, just a suggestion, I have discovered plain old rubbing alcohol is amazing as deodorant.

Yeah, the salt stick is similar to alcohol in that it just kills the bacteria causing the issue. The stick is small and easy to reapply if needed, it's just smooth simple salt.

No, I am not unburnable and definitely understand the dangers of excess UV radiation, but I can easily mitigate sunburn/extreme exposure by wearing long sleeves and a hat. I spend alot of time outdoors rock climbing and cycling. The few times I wear sunscreen are when I know I'll be unable to get in the shade or wear long sleeves (80 mile bike rides for the most part). I figure that moderate sun exposure while minimizing burns is probably more healthy than slathering on sunscreen.

I like the Toms stuff. Aquafresh burns, and most toothpastes leave me with a worse flavor in my mouth in the morning than Toms. I've always wondered why, but have been too disinterested to find out (and I suspect the answer is hotly debated).

I might give the salt stick a try... suggestions for a n00b?

Get a small squirt bottle and rubbing alcohol, and call it a salt stick. Works great, not kidding! :)

The salt stick was ineffective for me. I currently use Tom's deodorant instead.

Titanium dioxide is only suspected to be a carcinogen when inhaled in considerable concentration.

As it stands today, I wouldn't want to breathe concrete or tarmac dust in high concentration. Adding or refusing to add titanium dioxide will not alter my feelings on that. :)

I hadn't heard of this. Aren't many paints' pigmenting these days based on TiO2? Would sanding painted surfaces pose a risk?

> 1) There is already a large problem with excess nitrogen runoff due to fertilizers

Well, the NOx from car emissions don't exactly disappear into thin air :) .. the trick isn't to get rid of NOx, it's to keep humans from breathing it.

Right, because Humans are the only living thing on this planet. Converting one pollutant into another that doesn't directly affect us is not the solution.

The NOx is going in the environment anyway. This is trying to make it go there directly, instead of going via my lungs first.

More info on the effects of Nitrogen pollution: http://en.wikipedia.org/wiki/Dead_zone_(ecology)

Titanium dioxide is also used on the inside surfaces of windows, for the same purpose. I don't know how widespread its use is, though. http://en.wikipedia.org/wiki/Titanium_dioxide#As_a_photocata...

How nice would it be to have the negative aspects of vehicle use directly affected drivers?

The roads in the communities where they drive become toxic. Maybe we can create a diaper on exhaust ports of vehicles that is then scrubbed clean in their own drinking water.

Take the runoff water from the road with high nitrates and collect it in ditches with algae or Hydrilla absorbing CO2. Convert the algae/aquatic plants into bio diesel or dry it and make soil for plant nurseries.

Edit: Taken from Wikipedias Hydrilla article, "This abundant source of biomas is a known hyperaccumulator of Mercury, Cadmium, Chromium and Lead, and as such can be used in phytoremediation."

http://en.wikipedia.org/wiki/Phytoremediation

Can someone tell me, definitively, why we are trying to reduce NOx?

Yes, it comes out of tailpipes, and the stuff that comes out of tailpipes has always been deadly.

Yes, in high concentrations, it probably plays a part in LA's smogscape of the late 1900's.

Yes, my first car which made excessive NOx had a distinct smell and made me feel happy...

But did you know that NOx uses sunlight to produce free oxygen in a catalytic cycle? This free oxygen then reacts to produce ozone. Aren't we kind of having an ozone shortage right now?

Ozone near the earth's surface (which this road surface attacks) is a health risk, and contributes to smog. Ozone higher up in the atmosphere (of the famous "hole") blocks UV radiation.

http://www.policyalmanac.org/environment/archive/ozone.shtml

"...converts them with the aid of sunlight into harmless nitrate"

Genius! As soon as I read the article title, I realized the potential... Just think of all the energy the black road surfaces around the globe absorb!

Unfortunately, that energy is pretty low-grade and not very usable. Thus that heat absorption mainly just contributes to the "heat island" effect, which among other things increases air-conditioning costs. Better is to turn roads and roofs into reflecting surfaces, which generally improves the quality of urban areas.

http://en.wikipedia.org/wiki/Urban_heat_island

http://www.epa.gov/heatisld/

Scrubbing atmospheric pollution off with paint on the road is one of the stupidest ideas ever. Do they really think they can clean up such huge volumes of air like this? Some local authorities in London have already wasted a load of money trying to do this. Now the Dutch are at it.

As I read it, it's not paint, it's actually mixed into the concrete.

As far as whether it is effective or not... well, it's probably more effective than not doing anything (additional costs and construction techniques need to be considered). Overall, I think absorbing pollution near the vehicles that produce it is a good idea. The raw amount of paved area in the world makes it an attractive target for any 'green' development (I've heard of projects trying to put solar panels into roads).

As far as whether it is effective or not... well, it's probably more effective than not doing anything

That doesn't make sense. Resources are finite. If something is not effective, then you shouldn't be wasting time and money on it, definitely not public money.

The raw amount of paved area in the world...

Have you thought of the raw amount of air in the atmosphere?

... makes it an attractive target for any 'green' development

You hit on a good problem here. "Solutions" like this one end up being nothing but certificates for companies and governments to show that they are doing "sustainable green development (TM)".

One reason to battle the NOx at the road surface is that the concentrations there are higher, near where vehicles emit it. Thus you don't have to scrub as large a volume of air in order to get the same effect.

One HN-oriented analogy is conditioning heat out of a data center. If you wait till the heat coming off your servers mixes uniformly throughout the entire room, you have to process a lot of air. If on the other hand you catch the air just as it comes off the servers, you have to process less air in order to remove the same energy.

Pushing the analogy further-- at normal temperatures (for data centers and for the ultimate place they reject heat to, the outdoors), processing a small amount of air that starts at a high temperature can be done more cheaply than a large amount of air that starts very close to the temperature you want to maintain. By analogy, it's probably true that scrubbing a fixed amount of NOx is easier when you start at a high concentration, than when you have a greater volume at lower concentration.

Your data center analogy would make sense if we were talking about treating the exhaust at the tailpipe. Once the NOx is out in the atmosphere, it's already too late. NOx disperses very rapidly.

Further, think about the ratio of boundary layer (or even at a lower height) air volume to the surface area of roads. Plus, there is no suction happening here. It's literally just the air touching the surface of the road. I would love to see some numbers on the efficiency of this process, but my gut tells me it's pretty poor.

To get to your core comment, I agree that my analogy makes no claims about this scheme's efficacy. The posted article claims 25% to 45%, but who knows how ideal the conditions have to be to reach that level.

You are also absolutely correct that treating at the tailpipe is even better (for exactly the reasons my analogy makes clear).

That said, I will defend my analogy. My point was that dealing with NOx at the road surface will likely be more effective than dealing with it more generally in the atmosphere-- in part because the effective volumes aren't as huge as you might think (see the comment I was responding to), and in part because you're dealing with the NOx at higher concentrations.

I'm sure you're right that NOx disperses rapidly, but I'd bet that concentrations still are demonstrably higher at the roadway surface than, say, a block away. For example, this study found a factor of 5 difference between NOx at the side of a busy intersection, versus that some distance away: http://www.atmos-chem-phys.net/10/2745/2010/acp-10-2745-2010...

Second, I bet the boundary layer isn't all that thick at the road surface. After all, by definition you have cars passing along, stirring up a lot of turbulence. (Besides, even in quiescent conditions, you still get diffusive transport through the boundary layer, due to concentration differences-- and destroying NOx at the surface will set that up for you.)

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