Birmingham Clean Air Zone pollution cut 'smaller than thought'

The Clean Air Zone is focused on reducing levels of nitrogen dioxide produced by older cars and lorries

Birmingham's Clean Air Zone (CAZ) has had a smaller effect on pollution than was previously thought.

The CAZ is usually said to have reduced levels of pollution by about 13%.

Now scientists at the University of Birmingham say the drop is about half that at about 7%.

Reductions in levels of nitrogen dioxide (NO2) have been recorded in Colmore Row in the business district and in residential areas.

The CAZ is focused on reducing levels of NO2 produced by older cars and lorries.

It works by charging owners of more polluting vehicles a fee for entering the zone, nudging them to find an alternative instead.

The CAZ has worked in cutting NO2 levels but the scientists argue calculating the drop in pollution is much more complex than it first appeared.

Everything from the weather on a particular day to the seasons themselves can have an impact on those pollution levels.

What the researchers at the university have done is use clever maths to strip out all those various factors and just focus on the effect of the CAZ itself.

Rather than a 13% drop in NO2 levels, they say the effect is more like 7%.

Talking to one of the scientists who did the study, Prof Zongbo Shi, this does not mean the CAZ is not beneficial to the city.

The effect may be lower overall, but it is still very much there.

This is very apparent when you use the research to zoom in to street level - you can see a drop in NO2 in Colmore Row in the business district, as people ditch their polluting vehicles.

But you see a similar drop in places like Ladywood, where people actually live.

Scientists at the University of Birmingham say the drop in levels of pollution is about 7%

The research also shows the CAZ has a beneficial "spillover" effect at the edges.

Rather than people driving polluting vehicles further around the CAZ, making the problem worse at the edges, people appear to be leaving them at home.

To improve the air and the health of everyone living in Birmingham, it may well be the CAZ is a first step.

In the future we may need to look not just at cars, but at wood-burning stoves, boilers and sources of pollution from outside the city.

The CAZ looks to be working on cutting pollution but this research shows there is still a long way to go.