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The optical properties of particulate-matter aerosols, within the context ofexoplanet and brown dwarf atmospheres, are compared using three differentmodels: Mie theory, Modified Mean Field (MMF) Theory, and Discrete DipoleApproximation (DDA). Previous results have demonstrated that fractal hazeparticles (MMF and DDA) absorb much less long-wavelength radiation than theirspherical counterparts (Mie), however it is shown here that the opposite canalso be true if a more varying refractive index profile is used. Additionally,it is demonstrated that absorption and scattering cross-sections, as well asthe asymmetry parameter, are underestimated if Mie theory is used. Although DDAcan be used to obtain more accurate results, it is known to be much morecomputationally intensive; to avoid this, the use of low-resolution aerosolmodels is explored, which could dramatically speed up the process of obtainingaccurate computations of optical cross-sections within a certain parameterspace. The validity of DDA is probed for wavelengths of interest forobservations of aerosols within exoplanet and brown dwarf atmospheres (0.2 to15 micrometres). Finally, novel code is presented to compare the results ofMie, MMF and DDA theories (CORAL: Comparison Of Radiative AnaLyses), as well asto increase and decrease the resolution of DDA shape files accordingly(SPHERIFY). Both codes can be applied to a range of other interestingastrophysical environments in addition to exoplanet atmospheres, for exampledust grains within protoplanetary disks.

Aerosols are not Spherical Cows: Using Discrete Dipole Approximation to Model the Properties of Fractal Particles