

To clean the air, Dutch scientists invent pavement that eats smog - digisth
http://www.latimes.com/news/science/sciencenow/la-sci-sn-smog-eating-street-20130705,0,4941635.story

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haldujai
Some napkin math:

There are ~2.5 million miles of highways in the United States, for the sake of
easier math and a lack of statistics let us assume that this length of
pavement is responsible for all of the vehicular nitrous oxide emissions.

Transportation contributes 30% of total NOx emissions [2]. Lets assume that
the average highway is 4 lanes wide, giving a width of 62 feet.

Surface area = 2.5 million miles * 62 feet = 29 356 square miles.

The authors add 2.67 g per square meter of C-doped TiO2 (which has a lowball
estimated cost of ~$750 per metric ton.)

This gives us 203 000 tonnes or ~$150 million. This has to be applied 3x a
year (at least) to maintain ~%60 of maximal effectiveness of the TiO2 (20%)
over the year.

A generous estimate is that it is sunny ~1/3 of the time.

So to bring it all together, $450 million of raw materials would result in a
(1/3 * 60% * 20% * 30%) 1.18% reduction in NOx levels.

[1] Original Article:
[http://dx.doi.org/10.1016/j.jhazmat.2013.02.012](http://dx.doi.org/10.1016/j.jhazmat.2013.02.012)
(behind a paywall) [2]
[http://epa.gov/climatechange/ghgemissions/gases/n2o.html](http://epa.gov/climatechange/ghgemissions/gases/n2o.html)

Edit: Updated math, I used the wrong percentage of the contribution of motor
vehicle traffic, the correct figure is 30%, nevertheless the conclusion that
this would be a colossal waste of money still stands.

~~~
miahi
The TiO2 is not picky, it will also catalyze NOx from different sources, not
only cars.

~~~
haldujai
Not exactly, manufacturing plants release emissions very high into the air. To
my understanding the pavement has an effective radius of < 150m (from the
article).

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salmonellaeater
The title is a little misleading. Titanium dioxide has been known since 1967
[1] to act as a catalyst for oxidizing a wide range of compounds, including
nitrogen oxide (i.e. smog). Since at least 2002 it has been known to
significantly decrease smog when applied to road surfaces [2][3]. The
contribution here is another study (behind a paywall [4]) providing evidence
for TiO2's efficacy at reducing smog.

[1]
[http://en.wikipedia.org/wiki/Titanium_dioxide#Photocatalyst](http://en.wikipedia.org/wiki/Titanium_dioxide#Photocatalyst)

[2]
[http://www.italcementigroup.com/NR/rdonlyres/1F30E487-C0A2-4...](http://www.italcementigroup.com/NR/rdonlyres/1F30E487-C0A2-4D6F-AB6D-C14555FD866F/0/Scientificresults.pdf)

[3]
[http://www.time.com/time/specials/packages/article/0,28804,1...](http://www.time.com/time/specials/packages/article/0,28804,1852747_1854195_1854176,00.html)

[4]
[http://www.sciencedirect.com/science/article/pii/S0304389413...](http://www.sciencedirect.com/science/article/pii/S0304389413001210)

~~~
haldujai
This paper is about carbon doped TiO2, its synthesis was patented in 2005 and
is much more effective than regular TiO2.

~~~
salmonellaeater
_carbon doped TiO2_

Can you provide a reference? Did I link to the wrong paper? That's an
important detail and it's not in the article.

 _much more effective than regular TiO2_

How much more effective? The study done by Italcementi in 2002-2003
(admittedly not very trustworthy since it's done by the company that makes the
product) has numbers comparable to the Eindhoven study.

~~~
haldujai
_Can you provide a reference? Did I link to the wrong paper? That 's an
important detail and it's not in the article._

I'm not sure if you can get past the paywall but:

Section 2, paragraph 4, last sentence. "Carbon doped TiO2 from Kronos
International was used."

 _How much more effective?_

It varies from 2x-10x depending on the reaction conditions. Here is a paper
that shows 2x-4x based on a relatively primitive doping technique.

[http://dx.doi.org/10.1016/j.apcatb.2007.09.046](http://dx.doi.org/10.1016/j.apcatb.2007.09.046)

 _Italcementi_

Their TX Active may or may not be carbon doped, I couldn't find a straight
answer on their website. Self-cleaning TiO2 is almost certainly doped (Ag or
SiO2).

------
btbuilder
Seems like a cool idea but I'd be worried for the workers who have to dig up
the pavement as titanium dioxide dust is classified as potentially
carcinogenic. Perhaps the quantities in use are very small?

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dhughes
I read years ago about a car grill coated with something that also "ate smog",
but I guess cars don't have grills anymore or the project failed for some
other reason.

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jsumrall
Seems like the Technical University of Eindhoven is the place to be these
days.

------
contingencies
This is one of those inventions where if Daoist thought comes in to play it
allows you to laugh heartily at the folly of the entire proposition.

Observe: (1) The further you go from nature, the more problems you cause
yourself. (2) Concrete industry is one of the greatest polluters in the world.
(3) The impermeable nature of concrete is at once its weakness; by attempting
to block nature's course, it ensures both its own destruction and engenders
other problems such as flash floods. (4) Given the above, why make a new
concrete to 'improve' upon nature? Nature cannot be improved upon. Because
there is only one Way. (5) The Way that can be written is not the Way.

~~~
foobarbazqux
> (4) Given the above, why make a new concrete to 'improve' upon nature?

Smog-eating concrete isn't improving upon nature, it's improving upon not-
nature (which concrete clearly is according to points 2 and 3), thus bringing
it back closer to nature, and reducing the number of problems you cause
yourself, per 1. So, if you must build a Way, at least build it out of smog-
eating concrete.

~~~
contingencies
I wonder what famous Dutch hydraulic engineers and their environmental science
counterparts would say about removing natural water absorption in favour of
promoting runoff over chemical-laden surfaces. Similarly, I wonder if we
shouldn't look at such substances from the perspective of the overall energy
expended on their production, installation, maintenance and eventual disposal
over time.

~~~
foobarbazqux
The question isn't concrete vs. some environmentally friendly surface, the
question is concrete vs. smog-eating concrete, and whether the smog-eating
concrete is more environmentally friendly than regular concrete. Yes, total
cost to the environment over time is a consideration here.

~~~
contingencies
If you choose to artificially limit your scope of thought, then by all means
go ahead. However, any conclusions based upon such thinking will be similarly
limited. Personally I find more interest and utility in analyzing the
potential interactions of things on a broader scale.

There is some parallel here in conventional computing wisdom: _measure twice
cut once_ dictates that, given limited time, you're better off thinking a
course of action out before investing effort in creating something requiring
an ongoing investment of effort.

Thus, if the scope for this type of invention is environmental quality, why
not consider overall energy use and knock-on effects as part of your
evaluation?

~~~
foobarbazqux
I believe I just wasn't clear. In my first sentence I was clarifying the
discussion - we agree that no concrete at all is best if possible. In my
second sentence I was agreeing that it makes sense to consider energy use
before rolling out the supposedly greener concrete.

