From Nature:
Study after study has shown a connection between smoggy days and an increase in deaths. Now two experiments, one on mice and the other in men, clarify why. Diesel fumes, they find, encourage blood clots that can bring on heart attacks and strokes. The study in people helps to prove the correlation between heart problems and a city’s poor air quality and hints at the role of clotting in this process. And the work in mice exposed to smog suggests that the immune system kick-starts the process.
Together, the two call attention to the dangers of air pollution for people with heart trouble. “The message we’re trying to promote is please exercise, it’s good for your heart and your health. But if it’s a bad [air] day you should think twice,” says David Newby, a cardiologist at the University of Edinburgh, UK, who led the clinical study.
More here.