AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
A Low-cost Monitor for Simultaneous Measurement of PM2.5 and Aerosol Optical Depth
ERIC WENDT, Scott Kelleher, Lizette Van Zyl, Casey Quinn, Dan Miller-Lionberg, John Mehaffy, Jessica Tryner, Christian L'Orange, Bonne Ford, Azer Yalin, Marilee Long, Shantanu Jathar, Jeffrey R. Pierce, John Volckens, Colorado State University
Abstract Number: 583 Working Group: Instrumentation and Methods
Abstract This work developed and validated an outdoor monitor for simultaneous measurement of PM2.5 and aerosol optical depth (AOD): the AOD-UPAS. This instrument consists of an active air sampler (utilizing continuous and time-integrated measures of PM2.5) and four-channel sun photometer. Measurement of AOD is performed using low-cost, filtered photodiodes at four wavelengths (λ = 440, 520, 680, and 870 nm) that match those selected from the AErosol RObotic NETwork (AERONET). The AOD-UPAS is relatively low cost, solar powered, and operated using a mobile device (Bluetooth app for iOS and Android) for deployment in a citizen-science framework. The AOD-UPAS is compact, weighs approximately 500 g, and may operate autonomously for several days following setup and alignment.
Power management was optimized via Monte Carlo simulation of measured solar irradiance by season. Solar charging efficiency (6.7%) proved less than model assumptions (7.5%), however, the instrument is capable of near-continuous monitoring in Summer and 50% duty cycle in Winter. Instrument evaluation (and validation) was achieved through a series of laboratory and field deployments. The first deployment evaluated the PM2.5 monitor downwind from a large prescribed fire (n=50 samples). Mass concentrations measured near the burn ranged from 8 to 800 μg/m3 as 24-hr averages; co-located measurements with USFS reference monitors gave reasonable agreement (EBAM = -4.9 + 0.97[AOD-UPAS]; R2=0.92). The second deployment along the Colorado Front Range demonstrated moderate agreement between the AOD-UPAS and federal reference method samplers for gravimetric analysis of PM2.5 (48-hr averages). Bandpass of the photodiode array was approximately 15 nm at full-width half-maximum, which should be sufficient for valid AOD measurements under most conditions. Preliminary data suggest agreement within 10% when the AOD-UPAS was co-located with reference AERONOET instruments.