Dutch Town Lays Air-Purifying Concrete

eldavojohn writes "In an effort to combat air pollution, a Dutch town has paved some of its streets with air-purifying concrete. It contains a titanium dioxide-based additive that utilizes sunlight to turn car exhaust into harmless nitrates. It was shown to do this in a lab and now the scientists are interested in just how much this will affect the air quality around the road. They will sample the air quality by a normal road and by this newly paved one."

Offset?

Because the purifying concrete offsets the pollution incurred from mining the titanium to create the concrete? Am I wrong in thinking I knew an old lady who swallowed a fly? Someone weigh in on this please. Thanks :P

Re:Offset?

It might. If it works well enough, it would mean we could either remove catalytic converters from cars (which would increase engine efficiency), or promote the use of small diesels (which can be more fuel efficient but release a lot more NOx), and end up with a net win for smog pollution.

In other words, it doesn't directly do anything greenhouse gases, but it does allow us to produce less greenhouse gases by using techniques that produce more nitrates.

Re:Offset?

If it works well enough, it would mean we could either remove catalytic converters from cars (which would increase engine efficiency), or promote the use of small diesels (which can be more fuel efficient but release a lot more NOx), and end up with a net win for smog pollution.

An exhaust-eating road surface is never going to be as efficient as a guy just chasing your car down the street with a big vacuum cleaner hose. I think we're keeping our catalytic converters.

Re:Offset?

How, exactly, is removing the catalytic converter (which acts on the engine's exhaust just before it is expelled to the atmosphere) supposed to help improve engine efficiency? Do you realize what you just said is the equivalent of claiming that a new computer monitor will give you better CPU performance?

Because it's a flow restriction and the engine has to work to pump through it. In fact, particulate filters and catalytic converters and mufflers on new US diesel trucks harm the efficiency so much that it can do as much as 4 mpg damage.

Re:Offset?

The catalytic converter isn't as efficient as a straight pipe. While not legal, cutouts that push exhaust straight outside the engine and bypass the exhaust system do improve horsepower.

It's more like bumping up the speed of your front side bus on your CPU. If you have a slower FSB, you might not ever notice it if you aren't racing your ca... CPU. But when you need that speed, it sure would be nice to remove the FSB limitation.

That said, the amount of good that catalytic converters do means we should probably keep them, as they aren't a huge drain on the power of a vehicle.

Re:Offset?

The Titanium is not consumed in this process (merely a catalyst) so it might very well be worth it in the long run..

TFA interesting but light on details

All passive filters I know require replacement because they get clogged, or the active elements eventually decay. Beyond making jokes about swapping the church bricks five years from now, TFA was a bit light on the details. Does anyone know how does this works, from a chemical perspective?

Re:TFA interesting but light on details

I'm also a bit curious about the "harmless nitrates" [wikipedia.org] that will be washed into the ground every time it rains.

Re:TFA interesting but light on details

Nitrate is also known as a fertilizer.

Maybe that will cause people to think twice before,

    1. laying down fertilizer on their lawn, and shipping cut grass to landfills - leaving grass where it is provides the new grass with its own fertilizer.

    2. writing that nitrates can be worse than NOx (NO, NO2 and others)

NO3 is completely harmless compared to the more volatile cousins NOx that come out of tail pipes.

http://en.wikipedia.org/wiki/NOx [wikipedia.org]

Re:TFA interesting but light on details

http://en.wikipedia.org/wiki/Photocatalysis [wikipedia.org]
http://en.wikipedia.org/wiki/Titanium_dioxide [wikipedia.org]

TiO2 can catalyze a wide variety of chemical reactions in the presence of ultraviolet light (such as sunlight).

Nitrates?

Nitrates? Aren't those bad in their own right? I'm thinking along the lines of fertilizer run-off and the affect it has on algae in oceans. Could this solution create worse problems?

Re:Nitrates?

Anything is harmful in the wrong place and in the wrong concentrations. Nitrates are, for example harmful to fish in high concentrations.

Most systems have processes that are limited by the supply of some resource. Ocean ecosystems are nitrogen limited, whereas fresh water systems tend to be phosphorous limited. Thus if the nitrates are washed off into fresh water, they'll cause relatively little immediate damage unless the concentrations are high enough to be toxic. However, if that nitrate is carried downstream to the ocean, the plume of nitrogen rich water entering the ocean can cause blooms of organisms that use up so much oxygen that fin fish suffocate. This happens where the Mississippi enters the gulf.

So, how and where something like this is used makes a difference. If you imagine all the US cities along the Mississippi and its tributaries using it, and if there is a mechanism by which the nitrates make it into the rivers, then this could make the situation in the Gulf much worse. If you use it in a coastal city and only the runoff from that city affects the local ocean, the amount of nitrogen entering the ocean might or might not have any measurable effect.

Re:Nitrates?

"One thing I am worried about, though, is the color of these sidewalks. If they're using titanium dioxide, shouldn't they be a nice brown color?"

Actually titanium dioxide is quite white. It is used as pigment for white base paint.

Re:Nitrates?

The nitrates can't run off into the oceans, because Holland is below sea level.

Re:Nitrates?

a) Not all of Holland is below sea level, 75% of it is above sea level.

b) Nitrates can still pollute the ground water then diffuse into the ocean and rivers

How green?

This sounds like a great idea if it works, but surely producing concrete is a far from 'green' process. I wonder how long the concrete has to be in place to neutralise the polluting effect of manufacturing it in the first place.

Re:How green?

This sounds like a great idea if it works, but surely producing concrete is a far from 'green' process. I wonder how long the concrete has to be in place to neutralise the polluting effect of manufacturing it in the first place.

But we are producing concrete anyway, so we'll still be ahead as long as this process does not produce more pollution than the pollution from standard concrete + whatever it absorbs.

Re:How green?

What do you suggest paving the road with? Grass? Good intentions?

harmless nitrates ?

not to mention all the side products that are produced, msot of which i am willing to bet havenot even been identified, much less studied

J Environ Qual. 2008 Feb 11;37(2):291-5. Print 2008 Mar-Apr.Click here to read Links
        When does nitrate become a risk for humans?
        Powlson DS, Addiscott TM, Benjamin N, Cassman KG, de Kok TM, van Grinsven H, L'Hirondel JL, Avery AA, van Kessel C.

        Soil Science Dep, Rothamsted Research, Harpenden, Herts, UK.

        Is nitrate harmful to humans? Are the current limits for nitrate concentration in drinking water justified by science? There is substantial disagreement among scientists over the interpretation of evidence on the issue. There are two main health issues: the linkage between nitrate and (i) infant methaemoglobinaemia, also known as blue baby syndrome, and (ii) cancers of the digestive tract. The evidence for nitrate as a cause of these serious diseases remains controversial. On one hand there is evidence that shows there is no clear association between nitrate in drinking water and the two main health issues with which it has been linked, and there is even evidence emerging of a possible benefit of nitrate in cardiovascular health. There is also evidence of nitrate intake giving protection against infections such as gastroenteritis. Some scientists suggest that there is sufficient evidence for increasing the permitted concentration of nitrate in drinking water without increasing risks to human health. However, subgroups within a population may be more susceptible than others to the adverse health effects of nitrate. Moreover, individuals with increased rates of endogenous formation of carcinogenic N-nitroso compounds are likely to be susceptible to the development of cancers in the digestive system. Given the lack of consensus, there is an urgent need for a comprehensive, independent study to determine whether the current nitrate limit for drinking water is scientifically justified or whether it could safely

Wow, cool idea!

Maybe we could do even better.

Hmm, since we're being green anyway, lets eliminate some of the cars--then perhaps we could make the concrete softer to walk on.

We could use some other color but grey--yuck. Maybe green to represent the fact that it purifies the air.

Being softer, it would be nice if it had some kind of self-patching mechanism...

As long as it's going to be self-patching, let's get really sci-fi and have it create itself using some kind of a system involving materials from underneath itself in some kind of a synthesis process.

Damn, I'm thinking way too far ahead--our science will never get to the point where it can do this stuff. Guess I'll have to be happy with air-purifying concrete.

Meh...

Chicago is putting in water purifying concrete. [iht.com]

Hong Kong Polytechnic

I did some research for school over in Hong Kong for a few months and worked with the Hong Kong Polytechnic University Civil Engineering Dep. They used titanium dioxide coatings on bricks and highway noise barriers - actually in use in Hong Kong. They also have attached titanium dioxide nanoparticles to textiles to make filtering clothing:

http://www.polyu.edu.hk/cpa/polyu/hotnews/details_et.php?year=all&news_id=255 [polyu.edu.hk]

http://www1.polyu.edu.hk/hotnews/details_e.php?year=all&news_id=964 [polyu.edu.hk]

It's great to see it catching on...

Don't worry, though. It's completely harmless.

Harmless... [wikipedia.org]

In freshwater or estuarine systems close to land, nitrate can reach high levels that can potentially cause the death of fish. While nitrate is much less toxic than ammonia or nitrite, levels over 30 ppm of nitrate can inhibit growth, impair the immune system and cause stress in some aquatic species.[citation needed] However, in light of inherent problems with past protocols on acute nitrate toxicity experiments, the extent of nitrate toxicity has been the subject of recent debate.

In most cases of excess nitrate concentrations in aquatic systems, the primary source is surface runoff from agricultural or landscaped areas which have received excess nitrate fertilizer. These levels of nitrate can also lead to algae blooms, and when nutrients become limiting (such as potassium, phosphate or nitrate) then eutrophication can occur. As well as leading to water anoxia, these blooms may cause other changes to ecosystem function, favouring some groups of organisms over others. Consequently, as nitrates form a component of total dissolved solids, they are widely used as an indicator of water quality.

What could possibly go wrong, though? It's not like roadways are "surfaces" that might "runoff" into storm sewers or waterways.

For the system to be effective...

Nitrates don't need to be harmless, nor there needs to be zero side effects. All that's needed is that the combined damage produced by any side effects must be less than the damage produced by the excess carbon dioxide in lieu of said concrete.

Funny how any time there is a proposed innovation to solve a problem, there are always nitpickers who point out side effects without considering their proportion compared to the original problem being solved. A solution either offers a net benefit, or it doesn't.

Re:Human Problems?

1. Pave road with this stuff.
2. Drive diesel cars on roads.
3. Nitrates -> algae blooms in marshes just off road sids.
4. Harvest algae and press to make bio-diesel.
5. Profit.