Posted in | Climate Change | Pollution

Colorado Forest Study Offers Clearest Idea on Atmosphere's Organic Chemistry

An international group of Researchers came together on a small patch of ponderosa pine forest in Colorado for a few weeks during the summer of 2011 to perform one of the most comprehensive, lengthy surveys of atmospheric chemistry ever tried out in one place. In several cases, they used new measurement devices developed especially for this project.

“The goal was trying to understand the chemistry associated with organic particulate matter in a forested environment,” associate professor Jesse Kroll explains. “We took a lot of measurements using state-of-the-art instruments we had developed.” The team also took many photos while in Colorado. Pictured on the bottom right is Douglas Day, CU researcher and organizer of the field campaign. (Courtesy of the researchers)

Presently, after years of analysis, their detailed synthesis of the findings has been published this week. The teams, which comprised of a group from MIT using a newly-developed device to identify and quantify compounds of carbon, reported their collective results in a paper in the Nature Geoscience journal.

Jesse Kroll, MIT Associate Professor of Civil and Environmental Engineering and of Chemical Engineering, and James Hunter, an MIT Technical Instructor in the Department of Materials Science and Engineering who was a Doctoral Student in Kroll’s team during the period of the research, were Senior Author and Lead Author, respectively, of the 24 contributors to the report. Associate Professor Colette Heald of the Department of Civil and Environmental Engineering was also a Co-author.

The organic (carbon-containing) compounds they examined in that patch of Colorado forest play a crucial role in atmospheric chemical processes that can impact the health of the ecosystem, air quality and the climate itself. Yet a number of these processes are still poorly comprehended in their real-world complexity, and they had never been so thoroughly sampled, investigated and quantified in one place before.

The goal was trying to understand the chemistry associated with organic particulate matter in a forested environment. The various groups took a lot of different measurements using state-of-the-art instruments we each had developed.

Jesse Kroll, Associate Professor of Civil and Environmental Engineering and of Chemical Engineering, MIT

In doing so, they could fill in substantial gaps in the inventory of organic compounds in the atmosphere, discovering that nearly a third of them were in the form of formerly unmeasured semi-volatile and intermediate-volatility organic compounds (SVOCs and IVOCs).

We’ve long suspected there were gaps in our measurements of carbon in the atmosphere. There seemed to be more aerosols than we can explain by measuring their precursors.

Jesse Kroll, Associate Professor of Civil and Environmental Engineering and of Chemical Engineering, MIT

The MIT team, as well as some of the other research teams, created instruments that specially targeted these difficult to measure compounds, which Kroll defines as “still in the gas phase, but sticky.” Their stickiness makes it tough to push them through an inlet into a measuring device, but these compounds may play an important role in the development and modification of aerosols, miniature airborne particles that can add to smog or to the nucleation of ice crystals or raindrops, affecting the Earth’s climate.

“Some of these instruments were used for the first time in this campaign,” Kroll says. When examining the results, which provided unparalleled measurements of the SVOCs and IVOCs, “we realized we had this data set that provided much more information on organic compounds than we ever had before. By bringing the data from all these instruments together into one combined dataset, we were able to describe the organic compounds in the atmosphere in a more comprehensive way than had ever been possible, to figure out what’s really going on.”

It is a more complex challenge than what it appears, the Researchers mention. A very large variety of different organic compounds are constantly being released by trees and other vegetation, which differ in their physical properties, their chemical composition and their ability to react chemically with other compounds. As soon as they mix with the air many of the compounds start to oxidize, which exponentially increases their quantity and diversity.

The collaborative work to characterize the amounts and reactions of these diverse compounds took place in a section of the Manitou Experimental Forest Observatory in the Rocky Mountains of Colorado. Five different instruments were employed to gather the data on organic compounds, and three of those had never been used elsewhere.

Regardless of the progress, a lot remains to be done, the Researchers point out. While the field measurements provided a comprehensive profile of the quantities of different compounds over time, it could not identify the precise reactions and pathways that were converting one set of compounds to another. That sort of analysis requires the direct research of the reactions in a controlled laboratory setting, and that kind of work is continuous, in Kroll’s MIT lab and elsewhere.

Filling in all these details will make it possible to improve the accuracy of atmospheric models and help to evaluate such things as strategies to lessen specific air pollution issues, from ozone to particulate matter, or to evaluate the sources and removal mechanisms of atmospheric components that influence Earth’s climate.

The measurement team comprised of Researchers from the University of Colorado, the California Air Resources Board, the University of California at Berkeley, the University of Innsbruck in Austria, the National Center for Atmospheric Research, the University of Toronto, the University of California at Irvine, the Edmund Mach Foundation in Italy, Harvard University, Aerodyne Research, Carnegie-Mellon University, the University of Montreal, and the University of Washington. The research was funded by the National Oceanic and Atmospheric Administration.

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