Welcome back to our series on air quality! Last time, we talked about why air pollution matters. Today, the focus will be on the main causes of air pollution in London – and why the Volkswagen emissions scandal might have had some positive consequences after all. Again, Timothy Baker from the Environmental Research Group (ERG) at King’s has shared his knowledge with us, and given us his expert view on what governments should do to tackle pollution.
When it comes to the causes of pollution, many might be quick to blame large vehicles such as lorries. But according to Tim Baker, one of the main culprits for air pollution in London are diesel cars. They were often seen as the more environmentally friendly option compared to petrol cars, but while technology in petrol has improved rapidly in recent years, diesel cars have lagged behind. “The Department for Transport tested the 15 most popular diesel vehicles, and on average they were 4 to 7 times over the legal limit”, says Tim Baker in our interview. Petrol cars on the other hand only achieve somewhere around 10% of the emissions they are legally allowed to achieve, he claims. 
Under certain conditions, many diesel cars will also switch off their emission controls. Legal loopholes enabled them to do this when the outside temperature falls below 18°C. While manufacturers claim this is to protect the engine, average temperatures in London mean this causes significant problems for the city’s pollution levels, as cold periods are often when pollution builds up. This is made worse by the rising number of diesel vehicles on London’s roads.
“What we have seen is that the advances in technology in some vehicles have been massively offset by the change in fleet, especially in London. 10 years ago, probably around 15% of cars on the road were diesel. The year before last, more than half of the registered new cars were diesel.”
Some weather conditions can also contribute to higher pollution levels. Pollution can build up when it is not windy, and some of the worst pollution episodes happen on cold, foggy mornings when pollutants are trapped close to the ground. In addition to this, London’s geographical location means it may also be exposed to pollution from continental Europe. This is usually the case during spring, when wind carries pollution from the Netherlands, Belgium or France to London. However, the opposite is true for large parts of the year, carrying emissions from South East England to continental Europe. 
Therefore, even local pollution might require cross-border efforts to be tackled effectively. “It’s also someone else’s local emissions. And where are our local emissions going when they are not causing us a problem? They are going to somebody else”, says Tim Baker.
To solve London’s pollution problem, he says governments need to be brave, and not afraid to make difficult decisions. “Everyone says it’s the lorries. But if you actually want to solve the urban pollution problem in London, in a stroke, it’s ban diesel cars”, Tim Baker tells us in the interview. While this might be a drastic measure, he believes the public is now more aware of just how bad diesel vehicles are for air quality. “The Volkswagen emissions scandal did more for publicity than anything that has been done in the previous years of trying to get the story across”, the expert tells us, explaining that when the first London sites exceeded annual limits earlier this year, the press coverage had changed compared to previous years. “Usually they are calling us to explain why air pollution is bad for you. That didn’t happen this time – they actually started their articles with ‘We know air pollution is bad for you, it’s diesel that is causing it’.” As much of the changes to London’s car fleet have happened in the last 10 years, Tim Baker believes these changes should be reversible over the next 10 years. However, he is not sure governments are ready to do this:
“Is it likely to happen? Probably not. It should be possible, but I suspect there isn’t the bravery. I hope I’m proved wrong”
The next and final part of our air pollution series will focus on the actions each individual can take to both protect themselves from pollution, and to help clean up London’s air. In the meantime, you can follow us on Twitter and Facebook for more updates, as well as the ERG’s Twitter and website for regular pollution updates and forecasts.
