The Clean Air Act is estimated to save hundreds of thousands of lives every year. And now, new research suggests the legislation is even more effective than scientists first thought.
Air pollution in the US is a serious issue. In fact, in the US, the number of premature deaths associated with air pollution is even greater than the number of car accident fatalities every year.
But while there's still room for improvement, Americans would be a lot worse off without the Clean Air Act.
By regulating emissions of air pollutants and promoting research into cleaner alternatives, the EPA's 1970 Clean Air Act and additional amendments have successfully reduced the amount of particulate matter in the atmosphere.
And the cleaner air is saving lives.
In 2011 the EPA announced the legislation was responsible for over 100,000 lives saved every year from 2000 to 2010. But this is an understatment.
New research from MIT's Department of Civil and Environmental Engineering (CEE) suggests the EPA's legislation may have saved even more lives than first predicted.
That's because the initial report underestimated the decline of organic aerosol, a major component of atmospheric particulate matter and a massive contributor to air pollution.
"The EPA report showed a very large impact from the decline in particulate matter, but we were surprised to see a very little change in the organic aerosol concentration in their estimates," explained David Ridley, a research scientist in CEE and co-author of the study.
"The observations suggest that the decrease in organic aerosol had been six times larger than estimated between 2000 and 2010 in the EPA report."
Previous work has failed to focus on the long-term trend in organic aerosol, so the MIT study is the first of its kind.
Using data from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network, the researchers found organic aerosol decreased across the entire country in both the winter and summer seasons.
And it looks like the Clean Air Act is largely responsible.
When the researchers looked at NASA data, they found natural influences on organic aerosol, such as precipitation and temperature, had little effect on the decline.
In other words, the reduction in organic aerosol is occurring despite changes in cloud cover, rain, wildfires and temperature.
The results suggest it is changes in human behavior, not changes in the environment, that are responsible for this reduction.
To confirm this theory, the researchers created a model that compares emissions data to natural and anthropogenic sources of organic aerosol.
The researchers found over half of the decline in organic aerosol from 1990 to 2012 is accounted for by changes in human behavior, including vehicle emissions and residential and commercial fuel burning.
"We see that the model captures much of the observed trend of organic aerosol across the US, and we can explain a lot of that purely through changes in anthropogenic emissions. 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," said Ridley.
"This wasn't really something that the EPA was anticipating, so it's an added benefit of the Clean Air Act."
By measuring the amount of organic aerosol in the particulate matter samples, the researchers were then able to predict how much the levels decreased mortality from diseases like cardiovascular and repiratory disease.
"There are costs and benefits to implementing regulations such as those in the Clean Air Act, but 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 said.
"There are health benefits to reducing organic aerosol further, especially in urban locations. As we do, natural sources will contribute a larger fraction, so we need to understand how they will vary into the future too."
The study was published in the Proceedings of the National Academy of Sciences.