Calibration Factors of SidePak AM520 and PurpleAir Monitors for Tobacco and Marijuana Aerosols

Abstract

We conducted 24 experiments inside a residential room to determine the "calibration factors" - the ratios of gravimetric to optical PM2.5 - for SidePak and PurpleAir monitors to accurately measure tobacco and marijuana sources. Five SidePak AM520 and seven PurpleAir Zen monitors alongside two gravimetric filter samplers simultaneously measured tobacco (cigarette, cigar and vape), and marijuana (sativa joint, indica joint and vape) sources, each at 4 distinct source levels for linear regression. We included one SidePak AM510 (a prior version) and an Optical Particle Sizer (OPS3330) in some experiments for comparison. SidePak AM520 calibration factors for tobacco and marijuana smoking were comparable (0.13-0.14); they were smaller than marijuana vape (0.17). PurpleAir calibration factors showed the same trend but with larger values (0.41-0.44; 0.51). Tobacco vape calibration factors could not be determined by our filter samples. Therefore, we used an alternative density-based approach for calibration, involving the OPS monitor. We found marked, systematic differences between SidePak AM520 versus AM510 calibration factors. A separate experiment examined how much measurement errors can be reduced by predetermined calibration factors, using filter samples for validation. Compared to PurpleAir, SidePak AM520 more accurately estimated the gravimetric PM2.5 level after calibration (mean error = 4% versus 16%).