H. Langley DeWitt
B.S., Chemistry and English, 2003

AMS studies with application to early earth

Sometimes questions about atmospheric composition cannot be easily answered by field campaigns and ambient measurements—especially when other planets or other eras on earth are involved. We must use geological evidence, remote observations, and global aerosol models fitted with hypothetical chemical abundances to investigate the evolution of the atmosphere. Laboratory simulations can provide useful data on the chemical reactions hypothesized to occur in these remote atmospheres.

In our laboratory, we simulate photochemical organic hazes that may have covered the early Earth and also hazes that may cover the outer planets. We expose a variety of gas mixtures to either a broad-spectrum ultraviolet lamp or an electrical discharge energy source to simulate the energy sources available in these environments that would initiate aerosol formation. Currently, we are investigating the chemical and physical effects of an increased hydrogen mixing ratio on aerosols formed from carbon dioxide and methane in a nitrogen background, gases believed to have been present on the early Earth. We study the chemical and physical properties of these hazes using an Aerosol Mass Spectrometer (AMS) and a Scanning Mobility Particle Sizer (SMPS). These instruments allow us to analyze the aerosols in real time. The AMS gives us both the chemical composition of our particles and size information while the SMPS gives us complementary size information.

We are also investigating the optical properties of various haze particles—both simulated Titan and early Earth organic aerosols—using a Magee Scientific seven wavelength Aethalometer. We hope to extract absorption optical constants from our particles using this technique to begin answering questions about the UV shielding capabilities and anti-greenhouse effects of the organic hazes we simulate.

Current Tolbert Group

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