harms of air pollution

PM2.5 designates a near-ubiquitous air-polluting particle that frequently appears in the scientific literature as well as popular press news items. But few of us really know what they are talking about, mainly because it is just one characteristic of a complex category.
It’s been 50 years since cleaning up the air in the United States began in earnest. Skies are much clearer now than in the mid-20th century. Leaded gasoline is gone, power plants have been abandoning coal and sulfur dioxide has dropped by 91%. Despite these growing improvements, why have epidemiologists been unable to show the demonstrable public health benefits that their computer models predict?