Laboratory Infrared Spectroscopic Studies of Cloud Particle Formation and Growth on Titan, Mars, and Earth

Abstract:

Infrared spectroscopy is a valuable tool in laboratory studies exploring the thermodynamic and microphysical properties of cloud condensation throughout the solar system. Laboratory studies which provide the required nucleation and equilibrium information can improve the accuracy of microphysical modeling of cloud particles. Furthermore, by providing reference spectra collected under relevant conditions and plausible exposure and temperature histories, laboratory infrared studies can facilitate particle identification via remote sensing and can even shed light on processes which influence atmospheric particles.

The cloud nucleation and growth chamber of the Atmospheric Chemistry Laboratory at NASA Ames Research Center was designed to allow studies of condensable gases over ranges of temperature (145 – 200 K) and partial pressure (5e-8 – 5e-4 hPa) that mimic portions of the atmospheres of Earth and Mars. Recently this facility has been modified to study benzene condensation and growth in Titan's atmosphere as well. A silicon substrate is suspended in a stainless-steel chamber with KBr windows above and below to allow passage of an infrared beam. A liquid nitrogen cryostat allows the cooling of the substrate, and a kapton heater allows the temperature of the substrate to be adjusted via a temperature controller. Using a leak valve, gas phase molecular species can be introduced into the vacuum chamber. Temperature is measured with K-type thermocouples and pressure is measured with an ion gauge. Ice nucleation is monitored with a Fourier Transform Infrared (FTIR) spectrometer.

Highlights from work for Earth, Mars, and Titan will be presented, demonstrating the range of conditions and atmospheres studied to date. Spectra showing uptake of water in/on phyllosilicates under subsaturated conditions representative of the martian atmosphere will be discussed, as will new data showing variations in the spectrum of solid benzene as a function of formation temperature.