Hydrocarbon photochemistry in planetary atmospheres: Laboratory and observational investigations of organic aerosols

The role of photochemically-generated organic aerosols in planetary atmospheres is investigated with laboratory measurements of their formation rates and with observations of aerosol haze on Saturn's moon, Titan. Instrumentation has been developed to photochemically generate organic aerosols while simultaneously monitoring both the concentrations of gas phase species and the formation of organic aerosols. Measurements of concentrations and particle formation are made via mass spectrometry and light scattering, respectively. The photochemical formation of aerosols from pure CH4 is reported, which provides a dataset that may be used as a benchmark to test photochemical models of aerosol formation in planetary atmospheres. Measurements of particle formation in mixtures of CH4 and CO2 show that aerosol formation can occur at lower CH4/CO2 ratios than predicted by models, suggesting that particle formation on the young Earth and Mars may have occurred more readily than previously expected. Ground-based observations of Titan in the near-infrared, using adaptive optics, show that high-resolution spectral maps can determine the spatial and vertical profiles of atmospheric haze. Repeating these observations during the changing seasons on Titan will show how the photochemistry of particle formation couples with atmospheric circulation to seasonally redistribute aerosol hazes on a global scale.