In the west, the current range is 33-90 miles vs. a natural visibility of 140 miles. Fine particles can remain suspended in the air and travel long distances. For example, a puff of exhaust from a diesel truck in Los Angeles can end up over the Grand Canyon, where one-third of the haze comes from Southern California. Emissions from a Los Angeles oil refinery can form particles that in a few days will effect visibility in the Rocky Mountain National Park. Twenty percent of the problem on dirtiest days in that Park is attributed to Los Angeles-generated smog.
Airborne particles can also cause soiling and damage to materials.
Reduced risk of hospital admissions by thousands each year, and fewer emergency room visits, especially in the elderly and those with existing heart and lung diseases. Reduced risk of symptoms associated with chronic bronchitis, tens of thousands fewer cases each year. Reduced risk of respiratory symptoms in children, hundreds of thousands fewer incidences each year of symptoms such as aggravated coughing and difficult or painful breathing. Reduced risk of aggravation of asthma, hundreds of thousands fewer incidences each year, in children and adults with asthma. Reduced risks of susceptibility to childhood illnesses.