Evaluation of field calibration methods and performance of AQMesh, a low-cost air quality monitor

• Published in: Environmental monitoring and assessment 2021-05, Vol.193 (5), p.251, Article 251
• Main Authors: Wahlborg, Dan, Björling, Mikael, Mattsson, Magnus
• Format: Article
• Language: English
• Subjects: Air Pollutants - analysis; Air pollution; Air Pollution - analysis; Air quality; Airborne particulates; Ambient temperature; AQMesh; Atmospheric Protection/Air Quality Control/Air Pollution; Autumn; Bisquare linear fit; Calibration; Cleaning; Correlation analysis; Data; Data points; Earth and Environmental Science; Ecology; Ecotoxicology; Environment; Environmental Management; Environmental Monitoring; Environmental objective; Environmental quality; Environmental science; Error analysis; Hållbar stadsutveckling; Linear calibration; Low concentrations; Low-cost air quality monitor; Methods; Monitoring/Environmental Analysis; Nitrogen dioxide; Orthogonal regression; Outdoor air quality; Particulate matter; Particulate Matter - analysis; Particulate matter monitoring; Pollutants; Procedures; Quality standards; Seasons; Sustainable Urban Development
• ISSN: 0167-6369; 1573-2959; 1573-2959
• DOI: 10.1007/s10661-021-09033-x

Field calibrations of NO 2 , NO, and PM 10 from AQMesh Air Quality Monitors (AQMs) were conducted during a summer and an autumn period in a busy street in a midsize Swedish city. All the three linear calibration procedures studied (postscaled, bisquare, and orthogonal data) significantly reduced the ranges and magnitudes of the performance indicators to yield more reliable results than the raw data. The improvements were sufficient to satisfy the European Union (EU) Data Quality Objective (DQO) for indicative measurements as compared to reference data only for NO 2 (above 50 µg m −3 ) and NO (above 30 µg m −3 ) during the autumn calibration period. The relatively simple bisquare procedure had the best performance overall. The bisquare procedure improved the root mean square error by the same amount as other studies using complex multivariate calibration methods. Low concentrations of pollutants were measured, far below the EU Environmental Quality Standard thresholds and even satisfying the future goals for the Environmental Quality Objectives. Cleaning the raw data by removing data points in the reference data that were below the reference station limit of detections (and the synchronous data points in the AQM prescaled data) was found to improve the performances of the calibration procedures appreciably. Many NO 2 and almost all PM 10 data points in this study fell below the AQM limit of detection. These low concentrations will probably be a common problem in many field studies, at least in areas with relatively low air pollution. However, the relative errors were sufficiently low for these data points that they could be interpreted as accurately representing low concentrations and did not need to be removed from the datasets. For the NO 2 measurements, a slight periodic error correlated with sunlight and increased ambient temperature was noted. NO measurements correlated strongly with increased traffic.