October 15, 2009 | Preliminary research at NCAR suggests that biological particles may contribute significantly to the mass of organic carbon stored in atmospheric aerosols. The study is an important step for scientists who are just beginning to quantify the role that these biological particles play in the atmosphere.

Aerosols—tiny bits of solid or liquid suspended in the air—come from natural sources such as wind-blown dust, volcanic eruptions, and ocean salt, as well as from human sources such as fossil fuel burning. A significant fraction of atmospheric aerosols, in both polluted urban airsheds and more remote regions, consists of particulate organic carbon (POC). Despite this, scientists don't have a good understanding of the sources of POC in the atmosphere.

One potential source of atmospheric POC is biological particles such as bacteria, pollen, and fungal spores. NCAR scientist Christine Wiedinmyer and Gannet Hallar, director of the Storm Peak Laboratory in Steamboat Springs, Colorado, led an effort to measure these biological particles in March-April 2008 as part of the Storm Peak Aerosol and Cloud Characterization Study. The project brought atmospheric scientists and microbiologists together at a field site whose high-elevation location gave the researchers access to background concentrations in the atmosphere.

Wiedinmyer's results, published in June 2009 in Atmospheric Environment, show that biological particles could account for an average of 40% of the organic carbon mass in particles with diameters less than 10 microns. She cautions that the estimates are highly uncertain due to limitations on the study and the preliminary nature of the work.

"The hope is that this is the first step," Wiedinmyer says. "It's the start of a lot more research that will coordinate the efforts between the atmospheric and biological communities."

The team will return to the site in January-February 2010 for a second study that will produce a more detailed look at biological particles in atmospheric POC.

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