Current Topics in Geosciences

In the Air, in the Ocean and in the Soil: Photochemistry of Organic Matter Produces Reactive Oxygen Species / Dr. Nadine Borduas-Dedekind

Dr. Nadine Borduas-Dedekind, Dep. of Environmental Systems Science, ETH Zürich
In our bodies, reactive oxygen species (ROS) are products of the metabolism of oxygen and have biological roles in the functioning of organisms, including cell signaling. However, additional stresses like sunlight exposure, such as on our skin, can lead to overproduction of ROS and subsequent cell damage through oxidation. In aquatic environments, dissolved organic matter is an important source of ROS responsible for the abiotic degradation of pollutants in our rivers, lakes and arguably oceans. In the soil, ROS are produced abiotically and microbially and take part in the natural cycles of healthy soils as well as are proxies for environmental stressors. But what about in the atmosphere? Are there ROS in quantifiable concentrations? If so, which transformations do they take part in?

In this seminar, I will share my group’s contributions to understanding one type of photochemically produced ROS, specifically singlet oxygen (¹O₂) in atmospheric organic aerosols. Indeed, organic aerosols have an atmospheric lifetime of approximately one week. During this time, these aerosols will be subjected to atmospheric processing including exposure to sunlight. We have found that photochemistry of organic aerosols produces ROS in-situ capable of transforming their chemical and physical properties, with implications for air quality and climate. Using furfuryl alcohol as a probe for ¹O₂, we determined steady-state concentrations of this oxidant and calculated ¹O₂ quantum yields for SOA samples. Subsequent quantification of OH radicals and peroxides allowed for the comparison of degradation rates between ROS species. We found that for typical molecules found in SOA such as amino acids (histidine, tryptophan, methionine), organo-nitrogen compounds (imidazole, indole, niclosamide) and phenolic compounds (hydroquinone, resorcinol) have a shortened lifetime by more than half when ¹O₂ reactivity is taken into consideration. To further understand the seasonal variability of ¹O₂, we are currently working on a one-year time series of PM₁₀ filters collected in Switzerland. It is becoming clear that ¹O₂ could be an important photo-generated oxidant within aqueous organic aerosols for the degradation of aerosol tracer molecules.

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