Sam is an expert in photochemistry with a focus on the design, calibration and deployment of state-of-the-art actinic flux instrumentation, radiative transfer modeling and calculation of photolysis frequencies. He joined NSF NCAR in 1998 and has led the Atmospheric Radiation Investigations and Measurements (ARIM) group since 2008. In this time, he has deployed on over 50 NSF, NASA, NOAA, and EPA funded field campaigns from the surface to the stratosphere and from the poles to the tropics. His research provides critical links between chemical processing, air quality, aerosol and cloud characterizations, climate impacts and satellite validation.