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Open AccessArticle

Practical Field Calibration of Portable Monitors for Mobile Measurements of Multiple Air Pollutants

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School of Chemistry, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, UK
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Department of Civil & Environmental Engineering, University of Strathclyde, James Weir Building, 75 Montrose Street, Glasgow G1 1XJ, UK
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Cambridge Environmental Research Consultants Ltd., 3 King’s Parade, Cambridge CB2 1SJ, UK
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NERC Centre for Ecology & Hydrology, Bush Estate, Penicuik EH26 0QB, UK
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European Centre for Environment and Health, University of Exeter Medical School, Knowledge Spa, Royal Cornwall Hospital, Truro TR1 3HD, UK
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School of GeoSciences, University of Edinburgh, Crew Building, Alexander Crum Brown Road, Edinburgh EH9 3FF, UK
*
Author to whom correspondence should be addressed.
Atmosphere 2017, 8(12), 231; https://doi.org/10.3390/atmos8120231
Received: 20 October 2017 / Revised: 16 November 2017 / Accepted: 18 November 2017 / Published: 23 November 2017
(This article belongs to the Section Air Quality)
To reduce inaccuracies in the measurement of air pollutants by portable monitors it is necessary to establish quantitative calibration relationships against their respective reference analyser. This is usually done under controlled laboratory conditions or one-off static co-location alongside a reference analyser in the field, neither of which may adequately represent the extended use of portable monitors in exposure assessment research. To address this, we investigated ways of establishing and evaluating portable monitor calibration relationships from repeated intermittent deployment cycles over an extended period involving stationary deployment at a reference site, mobile monitoring, and completely switched off. We evaluated four types of portable monitors: Aeroqual Ltd. (Auckland, New Zealand) S500 O3 metal oxide and S500 NO2 electrochemical; RTI (Berkeley, CA, USA) MicroPEM PM2.5; and, AethLabs (San Francisco, CA, USA) AE51 black carbon (BC). Innovations in our study included: (i) comparison of calibrations derived from the individual co-locations of a portable monitor against its reference analyser or from all the co-location periods combined into a single dataset; and, (ii) evaluation of calibrated monitor estimates during transient measurements with the portable monitor close to its reference analyser at separate times from the stationary co-location calibration periods. Within the ~7 month duration of the study, ‘combined’ calibration relationships for O3, PM2.5, and BC monitors from all co-locations agreed more closely on average with reference measurements than ‘individual’ calibration relationships from co-location deployment nearest in time to transient deployment periods. ‘Individual’ calibrations relationships were sometimes substantially unrepresentative of the ‘combined’ relationships. Reduced quantitative consistency in field calibration relationships for the PM2.5 monitors may have resulted from generally low PM2.5 concentrations that were encountered in this study. Aeroqual NO2 monitors were sensitive to both NO2 and O3 and unresolved biases. Overall, however, we observed that with the ‘combined’ approach, ‘indicative’ measurement accuracy (±30% for O3, and ±50% for BC and PM2.5) for 1 h time averaging could be maintained over the 7-month period for the monitors evaluated here. View Full-Text
Keywords: air pollution sensor; air quality; O3; NO2; PM2.5; black carbon; personal exposure air pollution sensor; air quality; O3; NO2; PM2.5; black carbon; personal exposure
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Lin, C.; Masey, N.; Wu, H.; Jackson, M.; Carruthers, D.J.; Reis, S.; Doherty, R.M.; Beverland, I.J.; Heal, M.R. Practical Field Calibration of Portable Monitors for Mobile Measurements of Multiple Air Pollutants. Atmosphere 2017, 8, 231.

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