Evaluation of a low-cost optical particle counter (Alphasense OPC-N2) for ambient air monitoring

TY - JOUR

T1 - Evaluation of a low-cost optical particle counter (Alphasense OPC-N2) for ambient air monitoring

AU - Crilley, Leigh R.

AU - Shaw, Marvin

AU - Pound, Ryan

AU - Kramer, Louisa J.

AU - Price, Robin

AU - Young, Stuart

AU - Lewis, Alastair C.

AU - Pope, Francis D.

N1 - © Author(s) 2018

PY - 2018/2/7

Y1 - 2018/2/7

N2 - 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 °-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.

AB - 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 °-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.

UR - http://www.scopus.com/inward/record.url?scp=85041655877&partnerID=8YFLogxK

U2 - 10.5194/amt-11-709-2018

DO - 10.5194/amt-11-709-2018

M3 - Article

AN - SCOPUS:85041655877

SN - 1867-1381

VL - 11

SP - 709

EP - 720

JO - Atmospheric Measurement Techniques

JF - Atmospheric Measurement Techniques

IS - 2

ER -