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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 11, 709-720, 2018
https://doi.org/10.5194/amt-11-709-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
07 Feb 2018
Evaluation of a low-cost optical particle counter (Alphasense OPC-N2) for ambient air monitoring
Leigh R. Crilley1, Marvin Shaw2, Ryan Pound2, Louisa J. Kramer1, Robin Price3, Stuart Young2, Alastair C. Lewis2, and Francis D. Pope1 1School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK
2National Centre for Atmospheric Science, Wolfson Atmospheric Chemistry Laboratories, University of York, York, YO10 5DD, UK
3Birmingham Open Media (BOM), 1 Dudley Street, Birmingham, B5 4EG, UK
Abstract. A fast-growing area of research is the development of low-cost sensors for measuring air pollutants. The affordability 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 κ-Köhler 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.

Citation: Crilley, L. R., Shaw, M., Pound, R., Kramer, L. J., Price, R., Young, S., Lewis, A. C., and Pope, F. D.: Evaluation of a low-cost optical particle counter (Alphasense OPC-N2) for ambient air monitoring, Atmos. Meas. Tech., 11, 709-720, https://doi.org/10.5194/amt-11-709-2018, 2018.
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Short summary
The affordability and small size of low-cost particle sensors make them attractive for air pollution experiments that require multiple instruments, or take place in hard-to-access locations or low-income countries. For any sensor to be useful, its accuracy and precision need to be known. We evaluate the Alphasense OPC-N2 for monitoring airborne particles at typical UK urban background sites. The devices were found to be accurate provided they are correctly calibrated.
The affordability and small size of low-cost particle sensors make them attractive for air...
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