Smog-Eating Sidewalks: Concrete Treated with Titanium Oxide

[theoristo]

This is very interesting... The concrete is treated with titanium oxide and absorbs nitrogen oxide from the air. These measurements were taken from a study that installed the smog-scrubbing sidewalks on a city block in the Netherlands and monitored air quality over the course of a year.
here's the study http://www.ncbi.nlm.nih.gov/pubmed/23731840

 

[Greg Bernhardt]

I heard about this a few years back. I assume the major problem with it is cost?

 

[marcus]

The full text of the article is behind paywall BUT you get to see a lot of figures and captions free, including photographs and charts.
==sample captions==
Table 4. Average NOx concentration, absolute reduction and relative reduction for the measuring days without the presence of a photocatalytic effect: i) before street modification ii) after street modification and before the application of the first coating, iii) when the first and second coatings lost their abating ability, iv) rainy days (26/05/10 and 21/10/10) and v) very windy days (15/9/10).

Table 5. Average NOx concentration, absolute reduction and relative reduction for the measuring days with the presence of a photocatalytic effect: i) after first coating application and ii) after second coating application, excluding rainy days (26/05/10 and 21/10/10) and very windy days (15/9/10).
http://www.sciencedirect.com/science/article/pii/S0304389413001210
==sample text==
Highlights
► The results of a demonstration project for photocatalytic pavement are shown. ► The photocatalytic performance was studied in a street as well as on lab scale. ► The outdoor monitoring was performed in different seasons and weather conditions. ► The NOx concentration was in average 19% lowered by the photocatalytic street. ► Under ideal weather conditions the NOx reduction reached up to 45%.

Keywords
Photocatalytic pavement; Full scale demonstration; Air purification
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One thing I gather from what is immediately available free online is that the titania catalyst likes LOW HUMIDITY AND LOTS OF SUN, so it might be more practical in Los Angeles e.g. than in Seattle :^D
Also from photo and some wording it seems to me that they did not have to remove and replace a lot of material to do the experiment, it was more of a thin surface coating or a treatment of the existing pavement. But I could be wrong.
Also the catalyst went dead after a while. this happens with catalysts.

I have no idea if the idea is practical. In itself, I don't think Titanium dioxide is uncommon or necessarily expensive, it is the ore , the naturally occurring oxide of titanium, analogous to Alumina (bauxite). But there would be a lot of other costs, besides the raw material.
The thing is the idea has a kind of beauty, justice, appropriateness. Want to do go with internal combustion? Pave large areas of your city for the things to run on? Well that pavement is getting a lot of sunlight and the vehicles are emitting a lot of NOx. Something chimes in somebody's head. *ding* It's nice.
Another link to the abstract:
http://www.ncbi.nlm.nih.gov/pubmed/23731840