The extent to which tropospheric aerosols impact the environment,
particularly with regard to climate and human health, remains quite
uncertain. Given their proximity to Earth's surface, such particles are
likely to contain mixtures of organic and inorganic materials. In
addition, they are likely to take on different shapes and have different
phases. Reducing the uncertainties in the role these particles play
requires detailed knowledge of the chemical and physical properties of
the materials they are made from. This work focuses on the retrieval of
mid-infrared complex refractive indices from the aerosol extinction
spectra of commercially available motor oils. There is reason to believe
that motor oils could contribute organic material to tropospheric
particles, especially in urban areas with high concentrations of
internal combustion processes. Refractive index data for these systems
can be used in remote sensing applications to measure, amongst other
things, composition and particle size. The motor oil results will be
compared to refractive indices of long-chain hydrocarbons recently
measured in the laboratory. The image shown is a complex refractive
index set for a 5W-20 motor oil taken across the mid-infrared.