Here’s one for the thinking-out-of-the-box crowd. A research team at the Eindhoven University of Technology (TU/e) in the Netherlands have invented a type of paving material that can be mixed in with normal asphalt or concrete that actually removes some pollutants from the air as cars travel over the surface. The effect works well enough to remove some 25% to 45% of nitrogen oxides from vehicle emissions.
The best part: the material reportedly doesn’t even cost that much more than a normal roadway to construct.
Although modern vehicles are equipped with stringent emissions control equipment, exhaust still contains enough nitrogen oxides (NOx) to create concern for causing acid rain and smog. To combat this problem in a way that’s agnostic of the vehicle type, the researchers impregnated a paving material with titanium dioxide. The titanium dioxide works in conjunction with sunlight to cause a chemical reaction that removes the nitrogen oxide from the air and converts it into nitrate. The researchers say that the nitrate is then rinsed away by rain.
The research team has been working on the material for quite some time, but was only able to conduct its first area-wide tests this past year. Last fall around 1,000 square meters of existing road surface were covered with the air-purifying concrete paving stones, and another 1,000 square meters was surfaced with normal paving stones for comparison. Taking measurements at various levels between 0.5 and 1.5 meters above the road surface on both types of paving stones, the researchers found that the nitrogen oxides are reduced by almost half from the air immediately around the vehicles.
According to the researchers, the material also has another advantage: it can break down algae and dirt, keeping the surface relatively clean.
As interesting as this announcement is, I see a couple of issues that need to be addressed. Firstly, even though the researchers say that the material “only” costs 10% more to install than traditional road materials, if you’re talking about a couple hundred million dollar project, that’s not a small amount of additional budget for a municipality to cough up. If it could be conclusively proven that over time the material would pay for itself in, say, cleaning costs or in some other way (e.g. if an actual money value was put on the damage NOx pollutants do to the environment), then that might work out economically.
Secondly, although the researchers downplay the fact that all of the captured NOx pollution is washed away as “harmless” nitrates, it seems to me it’s just trading one form of pollution for another. Ask any agricultural area if they have a problem with nitrate pollution of their groundwater and you’re bound to get an emphatic “yes.”
Nitrate, as most of you probably know, is a fertilizer. It’s how plants get the critical nitrogen that they need. It’s also very mobile in soils, which means that instead of being captured in the soil for the plants to use later as most nutrients are, it tends to be washed through the soil and collect in deep groundwater reservoirs. Excess nitrate in drinking water has been connected to health issues in adults and “blue baby syndrome,” where a baby turns blue because the nitrogen stops it from being able to extract oxygen from the air.
Clearly, if our roads were made of this material, a huge amount of nitrate would be rinsing into the soil right underneath the roads, eventually reaching our groundwater and then some of it leaching out into our lakes and rivers and, potentially, causing algal blooms and killing off fish and the like. So, unless there’s some way to capture the nitrate, I’m thinking they need to go back to the drawing board.
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