ROx radicals, comprising OH, HO2, and organic peroxy radicals ("RO2"), are key trace species in the atmosphere that greatly affect the oxidation of volatile organic compounds and the formation of ozone and secondary organic aerosol (both of which affect public health and climate change). Current understanding of these radicals is partially limited by available measurements and comparisons to models. We propose to measure total peroxy radicals using the UMass ethane chemical amplification sensor, in collaboration with numerous colleagues who will quantify other trace radicals (e.g., OH) along with supporting measurements (radical precursors, VOCs, etc.).