Sample Collection.

High school students between the ages of 16 and 18 were recruited from CART in Fresno, CA to evaluate the AMAS. Each student wore the AMAS for a 48-h monitoring period and students were eligible to participate in the pilot multiple times. All study procedures were approved by the Institutional Review Board at the University of California at Berkeley and participants either provided informed consent or assent with consent from their parent/ guardian.

For each 48-h sample period, five reference samplers were deployed alongside five AMAS prototypes (assigned to participants at random) to compare performance. The reference sampler consisted of a backpack containing a traditional personal sampler with a PM_2.5 size-selective inlet (PEM 761−203A, SKC, Inc., Eighty Four, PA, U.S.A.), a personal sampling pump (BGI OMNI 3000, Mesa Laboratories, Lakewood, CO, U.S.A.), and a 25 mm filter cassette (Figure S4). The AMAS filters were cut from Pallflex Fiberfilm (T60A20; Pall Life Sciences, Ann Arbor, MI) sheets using a 15 mm punch. The reference sampler used 25 mm filters cut from Pallflex Fiberfilm sheets (10 of 15) and 25 mm Teflon filters (5 of 15; PT25P-PF03; Measurement Technology Laboratories (MTL), Minneapolis, MN). The reference filter samples were collected at 4 L min⁻¹, while the AMAS collected filter samples at 1.5 L min⁻¹. Additionally, a research team member collocated and transported five AMAS between microenvironments for 48 h to evaluate instrument precision. After sampling, filters were sealed in plastic cassettes and stored at −20 °C until they were shipped to Colorado State University and analyzed for BC and OP (within 3 months of sample collection). At the conclusion of each sampling event, all of the data logged to the AMAS were removed from the AMAS solidstate memory and transferred to a secure server.