Later this week, we should see a milestone in the ongoing EPA review of national air quality standards for fine particle pollution. EPA is under a court agreement by June 30 to issue a "staff paper" summarizing recent science and putting forth the opinon of agency career staff on whether the existing standards should be made stricter. (Prediction: yes, they will make such a recommendation, but probably leave a lot of wiggle room for the political types.)
Clean Air Watch is working closely with the American Lung Association on this issue. The association has published some good background at http://www.cleanairstandards.org/article/articleview/395/1/41/.