Guardian: The 1952 London smog taught us that air pollution caused people to die in the days and weeks that followed a short period of very high pollution. If we could only prevent smog episodes then it was thought that the air would be safe. A study in the 1990s changed this view. Thousands of people living in six US cities were tracked over 14 years. Having allowed for smoking and other factors, people lived shorter lives in the most polluted cities, showing, for the first time, that the particle pollution...