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Motorways Are Building Roadside Barriers to Shield Towns from Pollution

But improving air quality isn't the same as actually tackling emissions.
The barrier being constructed. Image: Highways Agency

If you drive along the M62 motorway in the UK, you might soon notice a big wall around junction 18. If you live not too far from the same spot, you just might notice that the air's a little cleaner.

The Highways Agency announced a new pilot to build two “air quality barriers” at the side of the road, with the aim of improving air quality for nearby communities. The four-metre-high barriers will be built by September, and will undergo a year-long trial to see how effective they are at tackling emissions from the 142,000 vehicles that drive through the spot every day.

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There are all kinds of fun smog-guzzling walls out there, from chemical facades that suck up pollutants to photocatalytic cement and even giant smog-busting poems. Disappointingly, these new barriers don’t really count among those futuristic designs.

The hundred-metre-long wooden and steel barriers don’t have a special coating that absorbs or filters pollutants; rather, they “disperse” them. A Highways Agency spokesman told me they’re basically like shields, impenetrable to oxides of nitrogen—the idea being that the pollutants get pushed up and away rather than spreading out to local communities at ground level.

Image: Highways Agency

According to the announcement, “The results of international studies so far show the barriers can reduce the level of oxides of nitrogen (NOx) by up to 20 percent in some areas.” That’s referring to a Dutch study that found barriers four metres high cut nitrogen oxides by 20 percent at a position 10 metres behind them.

A 2008 study in the US also found that pollutants such as carbon monoxide and particulate matter were reduced by 15 to 50 percent when there was a “noise barrier” next to the road. However, in certain wind conditions, there were in fact greater pollutant concentrations behind the barrier than where no barrier was present.

The UK initiative will have monitoring equipment in front of and behind the barrier to run their own tests as to how effective the giant fence is at keeping out emissions up to 200 metres away. A spokesman told me that, depending on the results, they may increase the height of the barriers.

It’s no secret that the UK’s pollution is a problem; it’s so bad the EU is taking legal action, given that levels exceed limits that were supposed to be met years ago. The new barriers will be erected in Greater Manchester one of the 16 regions singled out by the European Commission as the worst offenders for regularly exceeding air pollution limits.

But while it’s necessary to improve the air quality close to roads, especially where pollution exceeds legal limits, these walls won't solve the root problem. Reducing pollution where it's particularly harmful is certainly no bad objective, but wouldn’t it be better to reduce emissions overall? Spreading the pollutants around might have a diluting effect, resulting in better air quality in the immediate vicinity, but they still have to go somewhere—and you can only build a shield so big.