  Constraining the complex refractive indices, optical properties and size of
brown carbon (BrC) aerosols is a vital endeavor for improving climate models
and satellite retrieval algorithms. Smoldering wildfires are the largest source
of primary BrC, and fuel parameters such as moisture content, source depth,
geographic origin, and fuel packing density could influence the properties of
the emitted aerosol. We measured in situ spectral (375-1047 nm) optical
properties of BrC aerosols emitted from smoldering combustion of Boreal and
Indonesian peatlands across a range of these fuel parameters. Inverse
Lorenz-Mie algorithms used these optical measurements along with simultaneously
measured particle size distributions to retrieve the aerosol complex refractive
indices (m=n+i{\kappa}). Our results show that the real part n is constrained
between 1.5 and 1.7 with no obvious functionality in wavelength ({\lambda}),
moisture content, source depth, or geographic origin. With increasing {\lambda}
from 375 to 532 nm, {\kappa} decreased from 0.014 to 0.003, with corresponding
increase in single scattering albedo from 0.93 to 0.99. For {\lambda} = 532 nm,
both {\kappa} and single scattering albedo showed no spectral dependency. We
discuss differences between this study and previous work. The imaginary part
{\kappa} was sensitive to changes in FPD, and we hypothesize mechanisms that
might help explain this observation.
