Development and Validation of a Low-Cost Monitor for Simultaneous Measurement of PM2.5 and Aerosol Optical Depth

Atmospheric particulate matter smaller than 2.5 microns in diameter (PM_2.5) impacts public health, the environment, and the climate. Reliable estimates of health and climate impacts require accurate measurements of surface-level PM_2.5 concentrations at a global scale. Satellite-based measurements of Aerosol Optical Depth (AOD) may be used to quantify surface-level PM_2.5 concentrations in regions where surface PM_2.5 monitors are unavailable, but the AOD:PM_2.5 ratio used for these predictions is subject to ongoing inquiry. Spatially dense, ground-based networks of accurate co-located AOD and PM_2.5 measurements are necessary to better define the AOD:PM2.5 ratio; however, the lack of integrated PM_2.5 and AOD monitors combined with the high cost ($10,000 - $45,000) of separate monitors has prevented such a network from being actualized.

We have developed a compact, low-cost (<$1000) monitor, known as the Aerosol Mass and Optical Depth (AMOD) sampler, capable of simultaneous measurement of AOD (at 440, 520, 680 and 870nm), filter-based gravimetric PM_2.5, and real-time PM_2.5 concentration. Real-time PM_2.5 measurements made by a the AMOD light-scattering sensor can be corrected post hoc relative to the gravimetric filter measurement. AMOD validation against an EPA Federal Reference Monitor gave an average error of less than 10% (r = 0.93) for filter-based PM_2.5 measurements; validation against AERONET sun photometers gave a mean error of less than 0.01 AOD units (<10% mean bias); validation against an EPA Federal Equivalent PM_2.5 Light-Scattering Monitor yielded an error of less than 2 µg m-3 after filter correction. Recent design improvements include motorized solar tracking for real-time AOD measurement and automated data streaming using a low-cost Wi-Fi module. The AMOD’s small size, durable design, low cost, and robust measurement capability make it less susceptible to the issues found with previous monitoring technologies, which sought to attain a spatially dense distribution of measurements of AOD and PM_2.5.