The effects of aerosol on night sky brightness and perception of city light domes

Attenuation of stellar visibility by light pollution is of increasing concern worldwide, as population, energy usage, and corresponding increases in artificial lighting continue to rise. Atmospheric aerosols, also associated with anthropogenic activities, both scatter and absorb light and thus contribute in complex ways to sky glow and to the perceived brightness of light domes. In this study we explored the role of varying aerosol optical depth on modeled night sky brightness, to understand how future scenarios of aerosol emissions might affect light pollution. To initialize the model, a light source was constructed to approximate Denver, and calculations were made along a line of sight for a viewer in Boulder. Aerosol properties, including size distribution, refractive index, and phase function, were obtained from a ten-year record of AERONET summertime observations in Boulder, the season with typically highest aerosol optical depths. The calculations were performed using the ILLUMINA model, a three-dimensional radiative transfer model specifically designed for the simulation of light pollution. We tested the sensitivity of the results to changes in the input aerosol characteristics. Specifically, we isolated AERONET observations from summer 2012 that were influenced by local wildfires and by long-range-transported smoke, and developed alternate aerosol models for these cases. Evaluating the impacts of these smoke aerosols on light pollution was motivated by their global importance, particularly since fire activity is projected to increase globally due to warming surface temperatures.