Abstract: Nonequilibrium populations of quasiparticle excitations plague superconducting circuits, causing errors in quantum processors. I will present our results using aluminum nanobridge Josephson junctions to detect quasiparticles as they trap and untrap in the junctions' internal Andreev bound states. By carefully studying the trapping and untrapping rates as a function of environmental conditions, we can find the quasiparticles' mechanisms of excitation, relaxation, and thermalization. I will further discuss novel filter designs that can eliminate the high-frequency radiation that generates the quasiparticles in the first place.