EOMF-20. Angularly-resolved measurements of light scattering by smoke from wildfires during FIREX-AQ

The open burning of biomass fuels is an important source of aerosols because they contribute significantly to the pre-industrial radiative forcing budget and they are a large source of aerosol in the modern era that is anticipated to increase due to climate change. The angular distribution of light scattered by these particles (i.e. scattering phase function) is a key parameter that determines the aerosol contribution to forcing. This information is typically included in radiative transfer models as the asymmetry parameter, g. In this work, we report direct measurements of g from the NOAA Laser Imaging Nephelometer (LiNeph) during the FIREX-AQ campaign. We compare these measurements with two conventional methods of estimating g. The first method is using Mie theory to calculate a scattering phase function using an aerosol size distribution and an assumed complex refractive index. The second method is using the Henyey-Greenstein approximation to relate the hemispheric backscatter measurements to g. In both cases, we find that the conventionally derived g is overestimated compared to the direct measurements for fresh smoke. When applied to a simple radiative transfer model, the directly measured g can result in 20% more cooling from fresh biomass burning aerosols versus when applying the conventionally derived g.