Calibration and assessment of electrochemical air quality sensors by co-location with reference-grade instruments
Name
amt-11-315-2018.pdf
Size
5.44 MB
Format
Adobe PDF
Checksum (MD5)
0fdddc15a4761c7dfb0c000407b2d287
Author(s)
Issacman-Vanwertz, Gabriel
Wallace, Lisa M. M.
Hagan, David Henry
Franklin, Jonathan Pfeil
Kocar, Benjamin David
Heald, Colette L.
Kroll, Jesse
Date Issued
January 2018
Journal
Atmospheric Measurement Techniques Discussions
Publisher
Copernicus GmbH
Citation
Hagan, David H. et al. “Calibration and Assessment of Electrochemical Air Quality Sensors by Co-Location with Reference-Grade Instruments.” Atmospheric Measurement Techniques Discussions (August 2017): 1–40 © 2018 Author(s)
Version
Final published version
Abstract
The use of low-cost air quality sensors for air pollution research has outpaced our understanding of their capabilities and limitations under real-world conditions, and there is thus a critical need for understanding and optimizing the performance of such sensors in the field. Here we describe the deployment, calibration, and evaluation of electrochemical sensors on the island of Hawai`i, which is an ideal test bed for characterizing such sensors due to its large and variable sulfur dioxide (SO₂) levels and lack of other co-pollutants. Nine custom-built SO₂ sensors were co-located with two Hawaii Department of Health Air Quality stations over the course of 5 months, enabling comparison of sensor output with regulatory-grade instruments under a range of realistic environmental conditions. Calibration using a nonparametric algorithm (k nearest neighbors) was found to have excellent performance (RMSE < 7 ppb, MAE < 4 ppb, r² > 0.997) across a wide dynamic range in SO₂ (< 1 ppb, > 2 ppm). However, since nonparametric algorithms generally cannot extrapolate to conditions beyond those outside the training set, we introduce a new hybrid linear–nonparametric algorithm, enabling accurate measurements even when pollutant levels are higher than encountered during calibration. We find no significant change in instrument sensitivity toward SO₂ after 18 weeks and demonstrate that calibration accuracy remains high when a sensor is calibrated at one location and then moved to another. The performance of electrochemical SO₂ sensors is also strong at lower SO₂ mixing ratios (< 25 ppb), for which they exhibit an error of less than 2.5 ppb. While some specific results of this study (calibration accuracy, performance of the various algorithms, etc.) may differ for measurements of other pollutant species in other areas (e.g., polluted urban regions), the calibration and validation approaches described here should be widely applicable to a range of pollutants, sensors, and environments.
MIT Department
Massachusetts Institute of Technology. Department of Chemical Engineering
Massachusetts Institute of Technology. Department of Civil and Environmental Engineering
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
Terms of Use
Creative Commons Attribution 4.0 International License
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.5194/AMT-2017-296
