Abstract: Disclosed herein are instruments and related methods for measuring oxidative potential (OP) in airborne particulates, particularly PM2.5. The instrument is formed from three main components: a sample injector, a sample incubator and a measurement system. The instrument provides an automatic measure of five OP endpoints in a relatively rapid time frame of less than 3 hours. In this manner, additional parameters beyond the gross particle concentration or mass per unit volume is obtained, including the biologically-relevant OP associated with PM2.5.