A team of lead scientists at the California Institute of Technology has unlocked a major piece of the pollution puzzle. Their research was focused on the process by which gases emitted from plants become aerosols, or airborne microscopic particles. Led by professors Paul Wennberg and John Seinfeld of Caltech, the study focused on biogenic emissions. These organic carbon compounds are a result of chemical reactions that take place during the creation of aerosols in the atmosphere.

When people think of aerosol in the atmosphere they often blame hairsprays and cleaning solutions, but in fact not all atmospheric aerosols are a result of human production. “If you mix emissions from the city with emissions from plants, they interact to alter the chemistry of the atmosphere,” explained Wennberg. Plenty of research has been done on the effects of human emissions due to manufacturing and industrial production on the environment. However, the wealth of knowledge regarding the fate of biogenic emissions is not nearly so impressive. This informational deficiency regarding biogenic emissions was, in large part, the basis for the Caltech studies.

The researchers did an extensive case study on oak trees and their production of the chemical isoprene. This chemical is emitted by a large number of deciduous trees, though oak trees are the biggest contributors. Isoprene is known to be “one of the reasons that the Smoky Mountains appear smoky” Wennberg said.

“There is much more isoprene emitted to the atmosphere than all of the gases—gasoline, industrial chemicals—emitted by human activities, with the important exceptions of methane and carbon dioxide,” he stated. The study broke down the mystery of biogenic emissions by detailing the full chemical process of how they are converted and finally precipitated in the atmosphere. Once released into the atmosphere, Isoprene, which comes only from plants, is broken down by free-radicals. This oxidation process produces a small portion of so-called “secondary aerosols”. The study deduced that the trip from emissions to aerosols is not complete without a middle stage: epixode formation.

Epixodes are “nature’s glue” according to Wennberg. However, in order to become activated they have to come into contact with acidic particles. When an epixode and an acidic particle collide, the glue is activated and the epixode precipitates into the air, creating an aerosol which decreases visibility. Epixodes will bind at a higher rate in areas in which more acidic particles can be found in the air, namely, polluted cities.

More about this study can be found in the August edition of the journal Science where it was recently published. The study has an extensive description of atmospheric aerosol formation, and the adverse effects that it may have on human and environmental health. This topic is a very complex, yet potentially crucial one concerning pure air sustainability. It is for that reason that continued awareness through research and publication is such a major goal in the scientific community.

Article Link: http://www.sciencedaily.com/releases/2009/08/090806141518.htm
Journal link: http://www.sciencemag.org/cgi/content/abstract/325/5941/730

Discussion question: How might Carbon Dioxide and Methane emissions complicate the issue of air pollution?