Approximately one giga-ton carbon per year of volatile organic compounds (VOCs) is released into our atmosphere from man-made and natural sources, of which approximately 90% is from biogenic sources. Most of the organic compounds are processed within the lowest part of the atmosphere (troposphere) by oxidation reactions, which lead to oxidized organic compounds, particles and ozone, all of which are harmful to humans and the environment. Actions to improve air quality are guided by the predictions of numerical models, which include chemical reaction schemes. A detailed understanding of the underlying oxidation processes of organic compounds is necessary for accurate predictions.
The most important oxidant agent in the troposphere is the hydroxyl radical (OH) mainly produced by photochemical reactions driven by sunlight. Its outstanding importance for the oxidation capacity of the atmosphere relies on its quasi-catalytic cycling: After VOCs have been attacked, peroxy radicals are produced, which can regenerate OH, so that one OH radical originating from photolysis can oxidize a large number of VOCs before being lost in radical termination reactions. Understanding the recycling mechanisms is essential to predict the removal rate of pollutants out of the atmosphere and the formation of secondary pollutants such as ozone and particles. Recommendations for actions to improve air quality are based on the knowledge of atmospheric oxidation processes driven by radical chemistry.
In order to improve our understanding of atmospheric oxidation processes, simulation experiments in the unique large outdoor chamber SAPHIR at Forschungszentrum Jülich were performed. In order to ensure high accuracy of data, quality-assurance is essential. Therefore, one objective of the project was to develop instrumentation for the detection of short-lived atmospheric radicals and organic compounds.
By combining highly precise and accurate measurements in simulation experiments and quantum-chemical calculations, it could be shown that new reaction pathways of peroxy radicals impact the radical regeneration rate specifically in forested environments. The project significantly contributed to a better understanding of chemical atmospheric processes in these regions that lead to the formation of secondary pollutants in the oxidation chain of biogenic organic compounds. Results have been published and can now be implemented in chemical models used for air quality and climate warming predictions.
