At the heart of the VW revelations are tests for exhaust emissions of nitrogen oxides. These are a family of pollutants that become dominated by nitrogen dioxide as they mix in the air, causing most UK cities and towns to exceed World Health Organisation guidelines.
Defra estimates that the UK death rate is 4% higher due to nitrogen dioxide pollution – around 23,500 extra deaths per year. This has a massive cost to society – around £13bn per year or 0.7% of our gross domestic product.
This is a lot of money, but what does it mean for the average driver? Assuming official exhaust test limits, a 10-year-old diesel car driven in a big city for the UK annual average mileage of 10,700 miles has a health impact of £196 per year. For the latest technology diesel, this should be £63.
However, the pollution from cars in the real world is very different to the official tests. In road tests a typical 10-year-old diesel car produces nearly four times more nitrogen oxides than expected – an annual health cost of around £790 for an extra car in a big city.
Latest technology diesel cars emit, on average, seven times their test emissions when used on the road – an annual health cost of around £440 for an extra car. For a modern petrol car it would be less than £35.
Location is important too: nitrogen dioxide exhaust in typical big cities causes five times as much harm as it does in the countryside.
Annual road tax is the same for diesel and petrol cars; zero to £255 depending on carbon dioxide emissions and not on health-harmful air pollution.