Design and Validation of the Aerosol Mass and Optical Depth (AMOD) Monitor for Autonomous Measurement of Aerosol Optical Depth and Fine Particulate Matter

Remote sensing observations of aerosol optical depth (AOD) have been used to derive global estimates of surface fine particulate matter (PM 2.5 ) for studies on human health and the earth system. However, these estimates are uncertain due to a lack of measurements available to validate both the satellite AOD and the derived PM 2.5 products, which rely on the ratio of surface PM 2.5 to AOD. Traditional monitoring of these two air quality metrics is costly and cumbersome, leading to a lack of surface monitoring networks with high spatial density. The Aerosol Mass and Optical Depth (AMOD) sampler is a low-cost, portable instrument capable of taking high-quality, concurrent measurements of AOD and PM 2.5 . Building off previous work, we present an autonomous version of the AMOD, capable of unsupervised, semi-continuous measurement of AOD and PM 2.5 . The AMOD includes a set of four optically filtered photodiodes for multi-wavelength (440, 500, 675, and 870 nm) AOD, a Plantower PMS5003 sensor for time-resolved optical PM measurements, and a pump and cyclone system for time-integrated gravimetric filter measurements of particle mass/composition. The AMOD uses low-cost motors and sensor data for autonomous sun alignment to provide the semi-continuous AOD measurements. Operators can connect to the AMOD over Bluetooth® and configure a sample using a smartphone application. A Wi-Fi module enables real-time data streaming and visualization on our website.

We will discuss the development of the AMOD and present validation results from co-located experiments with traditional monitoring instruments (AERONET sun photometers and Federal Equivalent Methods for PM 2.5 ). Additionally, we will provide examples of field measurements taken by AMOD instruments deployed by citizen scientists in Colorado in 2019.