Air pollution rules aren't doing enough to protect Americans, finds a major new study that examined the cause of death for 4.5 million veterans, as The Guardian reported.

The scientists who published their research in the journal JAMA Network Open found that 99 percent of deaths from illnesses linked to air pollution stemmed from exposure lower than what the EPA allows, according to The Guardian.

The researchers pinpointed nine causes of death associated with exposure to fine particulate matter (PM2.5): cardiovascular disease, cerebrovascular disease, chronic obstructive pulmonary disease, type 2 diabetes, lung cancer and pneumonia. The scientists added three ailments not previously recognized — chronic kidney disease, hypertension and dementia, as Newsweek reported. PM2.5 is a mixture of pollution particles that are so fine they are roughly 30 times smaller than a strand of human hair, according to the New York State Department of Health, as Newsweek reported. Long-term exposure to PM2.5 has been linked to learning disorders in children, as well as a host of other conditions, including psychiatric disorders, depression, emphysema and lung disease. To measure the effect of PM2.5 in the U.S., the the researchers combined EPA air quality data with 10 years of medical records for 4.5 million U.S. veterans. Over the decade, 36.4 percent of the veterans (1,647, 071) died of various causes, including several linked to air pollution. From there, they established links between chronic PM2.5 exposure and nearly 200,000 deaths.