That's because theres so many, people are making the move to small diesels because they are fairly 'green' compared to petrol but that doesn't mean they are non polluting. All you have to do is look at cities in China or US cities such as LA where everyone drives petrol cars, pollution is the highest in the world. I can't say much as i drive a huge petrol car, but I moved out of the UK so i can haha
Maybe you should go and set ITV right as it's in conflict with their report yesterday ITV London News London Air Pollution Fri 11th July 2014Still plenty of nasty stuff in our air in London due to Diesel.
There used to be problems with sulphur dioxide from diesel emissions but all diesel sold now has a super low sulphur content, almost eliminating the problem. Diesels produce much less CO2 as the carbon isn't in suspension hence why you can see it as black soot. This is nothing anyway, search diesel smoke and see what the americans do!!!