Calibration and assessment of electrochemical air quality sensors by co-location with regulatory-grade instruments
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 d...
| Main Authors: | , , , , , , |
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| Format: | Article |
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Copernicus GmbH
2018
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| Online Access: | http://hdl.handle.net/1721.1/114971 https://orcid.org/0000-0001-5111-4671 https://orcid.org/0000-0001-8352-5854 https://orcid.org/0000-0003-2894-5738 https://orcid.org/0000-0002-6275-521X |
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| author | Wallace, Lisa M. M. Hagan, David Henry Isaacman, Gabriel Franklin, Jonathan Pfeil Kocar, Benjamin David Heald, Colette L. Kroll, Jesse |
| author2 | Massachusetts Institute of Technology. Department of Chemical Engineering |
| author_facet | Massachusetts Institute of Technology. Department of Chemical Engineering Wallace, Lisa M. M. Hagan, David Henry Isaacman, Gabriel Franklin, Jonathan Pfeil Kocar, Benjamin David Heald, Colette L. Kroll, Jesse |
| author_sort | Wallace, Lisa M. M. |
| collection | MIT |
| description | 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 (SO 2 ) levels and lack of other co-pollutants. Nine custom-built SO 2 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 < 7ppb, MAE < 4ppb, r2 > 0.997) across a wide dynamic range in SO 2 ( < 1ppb, > 2ppm). 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 SO 2 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 SO 2 sensors is also strong at lower SO 2 mixing ratios ( < 25ppb), for which they exhibit an error of less than 2.5ppb. 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. |
| first_indexed | 2024-09-23T14:48:29Z |
| format | Article |
| id | mit-1721.1/114971 |
| institution | Massachusetts Institute of Technology |
| last_indexed | 2024-09-23T14:48:29Z |
| publishDate | 2018 |
| publisher | Copernicus GmbH |
| record_format | dspace |
| spelling | mit-1721.1/1149712022-10-01T22:36:30Z Calibration and assessment of electrochemical air quality sensors by co-location with regulatory-grade instruments Wallace, Lisa M. M. Hagan, David Henry Isaacman, Gabriel Franklin, Jonathan Pfeil Kocar, Benjamin David Heald, Colette L. Kroll, Jesse 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 Hagan, David Henry Isaacman, Gabriel Franklin, Jonathan Pfeil Kocar, Benjamin David Heald, Colette L. Kroll, Jesse 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 (SO 2 ) levels and lack of other co-pollutants. Nine custom-built SO 2 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 < 7ppb, MAE < 4ppb, r2 > 0.997) across a wide dynamic range in SO 2 ( < 1ppb, > 2ppm). 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 SO 2 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 SO 2 sensors is also strong at lower SO 2 mixing ratios ( < 25ppb), for which they exhibit an error of less than 2.5ppb. 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. United States. Environmental Protection Agency (Grant RD-83618301) 2018-04-26T19:27:08Z 2018-04-26T19:27:08Z 2018-01 2017-11 2018-04-24T14:16:53Z Article http://purl.org/eprint/type/JournalArticle 1867-8548 http://hdl.handle.net/1721.1/114971 Hagan, David H. et al.“Calibration and Assessment of Electrochemical Air Quality Sensors by Co-Location with Regulatory-Grade Instruments.” Atmospheric Measurement Techniques 11, 1 (January 2018): 315–328 © 2018 Author(s) https://orcid.org/0000-0001-5111-4671 https://orcid.org/0000-0001-8352-5854 https://orcid.org/0000-0003-2894-5738 https://orcid.org/0000-0002-6275-521X http://dx.doi.org/10.5194/amt-11-315-2018 Atmospheric Measurement Techniques Creative Commons Attribution 4.0 International License http://creativecommons.org/licenses/by/4.0/ application/pdf Copernicus GmbH Copernicus Publications |
| spellingShingle | Wallace, Lisa M. M. Hagan, David Henry Isaacman, Gabriel Franklin, Jonathan Pfeil Kocar, Benjamin David Heald, Colette L. Kroll, Jesse Calibration and assessment of electrochemical air quality sensors by co-location with regulatory-grade instruments |
| title | Calibration and assessment of electrochemical air quality sensors by co-location with regulatory-grade instruments |
| title_full | Calibration and assessment of electrochemical air quality sensors by co-location with regulatory-grade instruments |
| title_fullStr | Calibration and assessment of electrochemical air quality sensors by co-location with regulatory-grade instruments |
| title_full_unstemmed | Calibration and assessment of electrochemical air quality sensors by co-location with regulatory-grade instruments |
| title_short | Calibration and assessment of electrochemical air quality sensors by co-location with regulatory-grade instruments |
| title_sort | calibration and assessment of electrochemical air quality sensors by co location with regulatory grade instruments |
| url | http://hdl.handle.net/1721.1/114971 https://orcid.org/0000-0001-5111-4671 https://orcid.org/0000-0001-8352-5854 https://orcid.org/0000-0003-2894-5738 https://orcid.org/0000-0002-6275-521X |
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