Journal
ATMOSPHERIC MEASUREMENT TECHNIQUES
Volume 11, Issue 2, Pages 709-720Publisher
COPERNICUS GESELLSCHAFT MBH
DOI: 10.5194/amt-11-709-2018
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Funding
- EPSRC (Global Challenges Research Fund) [IS2016, IS2017]
- NERC National Capability programme ACREW
- NERC [NE/N007115/1]
- Natural Environment Research Council [NE/R017026/1, ncas10006, NE/N007115/1, NE/M021513/1, NE/P003109/1, NE/R000034/1, 1643899] Funding Source: researchfish
- NERC [NE/M021513/1, ncas10006, NE/N007115/1, NE/R017026/1, NE/P003109/1] Funding Source: UKRI
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A fast-growing area of research is the development of low-cost sensors for measuring air pollutants. The afford-ability and size of low-cost particle sensors makes them an attractive option for use in experiments requiring a number of instruments such as high-density spatial mapping. However, for these low-cost sensors to be useful for these types of studies their accuracy and precision need to be quantified. We evaluated the Alphasense OPC-N2, a promising low-cost miniature optical particle counter, for monitoring ambient airborne particles at typical urban background sites in the UK. The precision of the OPC-N2 was assessed by co-locating 14 instruments at a site to investigate the variation in measured concentrations. Comparison to two different reference optical particle counters as well as a TEOM-FDMS enabled the accuracy of the OPC-N2 to be evaluated. Comparison of the OPC-N2 to the reference optical instruments shows some limitations for measuring mass concentrations of PM1, PM2.5 and PM10. The OPC-N2 demonstrated a significant positive artefact in measured particle mass during times of high ambient RH (> 85 %) and a calibration factor was developed based upon kappa-Kohler theory, using average bulk particle aerosol hygroscopicity. Application of this RH correction factor resulted in the OPC-N2 measurements being within 33% of the TEOM-FDMS, comparable to the agreement between a reference optical particle counter and the TEOM-FDMS (20 %). Inter-unit precision for the 14 OPC-N2 sensors of 22 +/- 13% for PM10 mass concentrations was observed. Overall, the OPC-N2 was found to accurately measure ambient airborne particle mass concentration provided they are (i) correctly calibrated and (ii) corrected for ambient RH. The level of precision demonstrated between multiple OPC-N2s suggests that they would be suitable devices for applications where the spatial variability in particle concentration was to be determined.
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