In situ and solar radiometer measurements of atmospheric aerosols in Bozeman, Montana

Abstract

Atmospheric aerosols play a very important role in Earth's climate system. Aerosols provide one of the most significant uncertainties in the climate system, mainly due to aerosols differing greatly in different regions. Measuring these aerosols accurately and effectively is very important. Inversions of solar irradiance and sky radiance measured by solar radiometers, for example those within the AErosolROboticNETwork (AERONET), provide aerosol properties within different regions across the world. Aerosol properties retrieved by AERONET are generally found to be very accurate and have been a very reliable source for aerosol measurements, but there are concerns about the inversion accuracy in very clean environments with low aerosol concentration. In this thesis, accuracy assessments are done on some of the aerosol properties retrieved by the AERONET inversion using in situ instruments making aerosol measurements at the ground. First, Bozeman, Montana and the surrounding Gallatin Valley's aerosol characteristics are assessed to show why this area is a good place to do these studies. Then, the real part of the refractive index retrieved from AERONET is assessed and shown to be potentially about 3.5% too high during the study period for all aerosol concentration conditions. Lastly, the aerosol size distribution that is retrieved by AERONET is assessed and found to be very accurate under well-mixed conditions in the boundary layer. Overall, the AERONET inversions are very accurate during these very clean conditions, with evidence of small (~3.5%) linear biases in the real part of the refractive index.