Air pollution is one of the leading causes of death on the planet. The World Health Organization's 2014 study of mortality from air pollution found that about 3,000,000 people a year die from effects of "ambient" (outdoor) air pollution. 

Skepticat makes an excellent point, below, when he calls the AQI a "death index". Science probably knows about how much the mortality rate increases per percent of beta scatter, although this would vary given differing populations and geography.  

I wonder if anyone has correlated local emergency room admissions and the AQI. 

http://www.who.int/phe/health_topics/outdoorair/databases/en/