Read the full story from U.S. EPA.
During the summer of 2013, some 60 atmospheric scientists converged in Alabama, Tennessee, and North Carolina for one of the largest air monitoring studies in the region in two decades. Called the Southern Oxidant and Aerosol Study, the scientists set out to study everything they could about the physical and chemical interactions of many pollutants in the atmosphere. Among other inquiries, they wanted to more fully understand why the region was experiencing elevated levels of secondary organic aerosols (SOAs).
SOAs are air pollutants produced from emissions from trees and plants and human-made sources. They are produced through a complex interaction of sunlight, air pollutants from cars or industrial emissions, and other airborne chemicals. SOAs are also a major component in the production of fine particle pollution (PM2.5), which can cause or worsen lung and heart problems and other health effects. Trees provide many benefits, including natural beauty, shade, support of ecosystems, and absorption of carbon dioxide—a pollutant and greenhouse gas—but they also emit chemicals called volatile organic compounds (VOCs). Researchers from EPA, other agencies, and universities found that when VOCs from vegetation interact with human-made pollutants, air quality problems can get worse.
Prior research pointed to the mixing of human-made and naturally-emitted pollutants as a major factor in SOAs creation and therefore fine particle pollution, which is regulated under the National Ambient Air Quality Standards (NAAQS). The study confirmed that chemical interactions of these pollutants lead to more PM2.5 in the Southeast United States, a region that is heavily forested and contains large urban areas such as Atlanta…
These results are described in the paper, Additional Benefits of Federal Air-Quality Rules: Model Estimates of Controllable Biogenic Secondary Organic Aerosol, by Carlton et al.