This is ARM's airborne laboratory for atmospheric research, operated by Pacific Northwest National Laboratory on behalf of the U.S. Department of Energy (DoE). This G-159 was acquired and converted in 1987, initially operating for the DoE's Atmospheric Chemistry Program and later for their Aerosol Science Program. It served for the ARM program since 2010, and made its last operational landing on 17 Dec 2018 at its base at Tri-Cities Airport in Pasco, WA, after completing a scientific campaign in Argentina. It was replaced by Challenger 850 N850RJ in June 2019 which, following conversion and training, was expected to be ready for its ARM duties in 2023.