The US Environmental Protection Agency's (EPA) Clean Air Act has played a vital role in reducing the exposure of people to harmful pollutants and have saved more lives than initially reported, finds a study by MIT researchers.
The EPA Clean Air Act saved against atmospheric organic aerosol -- a major component of atmospheric particulate matter -- emitted directly from fossil fuel combustion, residential burning and wildfires.
Organic aerosol is also chemically produced in the atmosphere from the oxidation of both natural and anthropogenically-emitted hydrocarbons.
The EPA's 1970 Clean Air Act and additional amendments enacted in 1990 address the health effects of particulate matter, specifically by regulating emissions of air pollutants and promoting research into cleaner alternatives.
In 2011 the EPA announced that the legislation was responsible for a considerable decrease in particulate matter in the atmosphere, estimating over 100,000 lives saved every year from 2000 to 2010.
However, the new study found a more dramatic decline in organic aerosol across the US than reported earlier, and may account for more lives saved than the EPA anticipated.
"The observations suggest that the decrease in organic aerosol had been six times larger than estimated between 2000 and 2010 in the EPA report," said David Ridley, research scientist at MIT's Department of Civil and Environmental Engineering (CEE).
"The changes in organic aerosol emissions are likely to be indirectly driven by controls by the EPA on different species, like black carbon from fuel burning and nitrogen dioxide from vehicles," Ridley explained.
For the new study, published in the Proceedings of the National Academy of Sciences, the researchers simulated organic aerosol concentrations from 1990 to 2012 in a model.
The results showed that the organic aerosol decreased across the entire country in the winter and summer seasons, despite the increase in wildfires, cloud cover, rain and temperature changes.
More than half of the decline in organic aerosol is accounted for by changes in human emissions behaviours, including vehicle emissions and residential and commercial fuel burning, the researchers said.
While "there are costs and benefits to implementing regulations such as those in the Clean Air Act, it seems that we are reaping even greater benefits from the reduced mortality associated with particulate matter because of the change in organic aerosol", Ridley noted.
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