Photochemistry and Radicals

About

Our research aims for understanding, how pollutants are processed in the atmospheric in field and chamber experiments. Their chemical transformation leads to secondary pollutants such as hazardous ozone and particles. Detailed knowledge of the underlying chemical processes is key for understanding air quality. With our observations of radical and trace gas concentrations we can test current chemical mechanisms and discover so far unaccounted processes.

Research Topics

A large number of different organic compounds are emitted not only from human activity, but also from plants. Our research focus is the investigations of their chemistry under different chemical conditions that are representative for urban and remote conditions. Observations of specifically atmospheric radical species require highly sensitive instrument that we develop in our research group.

Approximately 109 tons carbon per year of volatile organic compounds (VOCs) are released into our atmosphere from man-made and natural sources, of which the majority (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. Our research aims for a detailed understanding of the underlying oxidation processes of organic compounds for accurate predictions.

The most important oxidant agent in the troposphere is the hydroxyl radical (OH) mainly produced by the photolysis of ozone and nitrous acid (HONO). OH radicals attack most of the organic compounds. Its outstanding importance for the oxidation capacity of the atmosphere relies on its quasi-catalytic cycling: After organic compounds 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 pollutants before being lost in radical termination reactions.

By observations of trace gas and radical concentrations in field and chamber experiments, we test our current understanding of chemical mechanisms by comparing observations to results of model calculations. Model-measurement differences indicate missing processes that can affect the formation of ozone and particles. Results from quantum-chemical calculations done by the group of Luc Vereecken help to identify the specific reactions that are responsible for the gaps.

Because there are no commercial instruments available, we develop our own instrumentation for the detection of radical and trace gases:

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Last Modified: 18.06.2024