News Release

Declining organic aerosols in the United States

Peer-Reviewed Publication

Proceedings of the National Academy of Sciences

Atmospheric organic aerosol is declining in the United States, mostly due to decreases in anthropogenic sources, according to a study. Exposure to atmospheric particulate matter is estimated to cause more than 4 million premature deaths globally each year. The combustion of organic matter, such as fossil fuels and forest fires, produces particulate matter, including organic aerosol (OA) and black carbon (BC), and OA also arises from the oxidation of volatile organic carbon. David Andrew Ridley and colleagues analyzed BC and OA surface concentrations from 1990 to 2012 across the United States. The authors found that OA and BC declined by 40% and 55%, respectively, during the time period studied, accounting for more than 30% decline in US particulate matter. The decline occurred despite an increase in wildfire-produced OA. Simulations using a US emissions database for OA and BC from 1990 to 2012 indicated that at least two-thirds of declining OA are linked with changes in anthropogenic emissions, primarily declines in vehicle emissions and residential wood burning. The authors estimate that the decreasing anthropogenic OA was responsible for averting approximately 180,000 premature deaths from 1990 to 2012. The unexpected decrease in OA resulted in approximately 84,000 more lives saved than anticipated by the US Environmental Protection Agency between 2000-2010, an overlooked benefit of the Clean Air Act, according to the authors.


Article #17-00387: "Causes and consequences of decreasing atmospheric organic aerosol in the United States," by David Andrew Ridley, Colette Heald, Kelsey Ridley, and Jesse Kroll.

MEDIA CONTACT: David Andrew Ridley, Massachusetts Institute of Technology, Cambridge, MA; tel: 857-260-0221; e-mail:

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