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.
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.
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).
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.
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.
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).
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?
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.
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.
> (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.
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.
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.
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?
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.
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 (behind a paywall) [2] 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.