AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Variability Between High Time-Resolution PM Data from Regulatory Instruments: Implications for Low-cost Sensor Evaluations
KAROLINE BARKJOHN, Ian VonWald, Joann Rice, Robert Vanderpool, Tim Hanley, Andrea Clements, U.S. EPA Office of Research and Development
Abstract Number: 66 Working Group: Air Quality Sensors: Low-cost != Low Complexity
Abstract High time-resolution data (e.g., 1-minute to 1-hour) from low-cost air sensors, including PurpleAir sensors, is increasingly used to explore local air quality. The performance of air sensors is often assessed by comparison to a regulatory instrument; in most cases these monitors have been characterized by comparison to 24-hour integrated mass filter data and little is known about their performance at higher time-resolution. In this work, collocated Teledyne T640x and Grimm EDM 180 instruments measuring PM10 and PM2.5 were compared for one year at a site in Durham, NC. During this period, gravimetric federal reference method (FRM) samples were collected daily for five months and three PurpleAir sensors were collocated for a separate three-month period. First, the error of the Grimm and T640x were determined versus the FRM on a 24-hour basis. Next, the relative measurement performance between the T640x and Grimm at various averaging intervals (1 minute to 24 hour) was compared and techniques aimed at improving the comparisons were explored. The results suggest these regulatory instruments can differ substantially at 24-hour averages and more at shorter averaging intervals. The large disagreement between monitors at short averaging intervals has implications for perceived sensor performance. This is demonstrated in our evaluation of PurpleAir sensors against both the Grimm and T640x over 1-minute to 24-hour averaging intervals. This work demonstrates that the selected comparison method may impact the calculated performance of an air sensor and highlights the limitations of comparing performance studies using different reference instruments. Future sensor evaluations should acknowledge the impacts of the comparison instrument type and should set reasonable expectations for sensor performance.
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