Atmospheric Chemistry Program Seminar: Nathan Reed, CU-ANYL Chem
The Effects of Trace H2S in Laboratory Experiments of Planetary Organic Haze Chemistry
Nathan William Reed,
Tolbert group / Browne group
CU ANYL Dissertation Defense
Planetary organic hazes from methane (CH4) photochemistry and atmospheric sulfur gases are each common in planetary atmospheres, including the Archean Earth and, likely, exoplanetary atmospheres. A planetary organic haze can affect a planet’s radiative forcing and interpretations of observable spectra, as well as act as a source for prebiotic chemistry and nutrients for life. However, cross reactions between inorganic sulfur and organic molecules to form organosulfur have yet to be explored in haze chemistry. The objective of my thesis is to explore the coupling between hydrogen sulfide (H2S) and organic haze chemistry. Here I present the results of laboratory experiments using aerosol mass spectrometry, differential mobility analysis, and optical measurements to explore how trace H2S influences the compositional, physical, and optical properties of aerosol from organic haze analogs produced by CH4 photochemistry. I investigated the chemistry of aerosol formed in reducing (CH4/H2S gas mixtures in N2, varying trace H2S) and weakly reducing (CO2/CH4/H2S gas mixtures in N2, varying CO2) atmospheric conditions.
When I included trace H2S in precursor mixtures, the total organic aerosol mass increased in both conditions, despite H2S not being a carbon source. Moreover, I found evidence for the formation of organic reduced sulfur (ORS) and organic oxidized sulfur (OOS) compounds in the reducing and weakly reducing conditions, respectively. At lower CO2 mixing ratios, I attributed the total sulfate signal to be entirely OOS. Thus, in contrast to previous thought, I show that ORS and OOS are potentially significant atmospheric sulfur reservoirs. Further, I found the compositional changes in the reducing conditions lead to changes in the aerosol optical properties, as the total extinction (absorption plus scattering) of light increased with increasing H2S mixing ratios. I found that trace H2S dramatically influences the organic aerosol composition, mass, and optical properties by the formation of organosulfur (ORS and OOS) compounds and enhancing organic aerosol formation. These results have implications for Archean atmospheric chemistry, prebiotic chemistry, planetary climate, and spectral interpretations for exoplanetary atmospheres.
Thus, future work should consider the potential impacts of trace H2S on organic haze chemistry.