A case study on the effect of contaminated inlet tubes on the accuracy of mid-cost optical particle counters for the ambient air monitoring of fine particles

Abstract

Abstract This study investigates the impact of the long-term use of inlet-heated tubes on the performance of mid-cost optical particle counters (OPCs) for ambient air monitoring of fine particles (PM2.5). Two OPCs, equipped with inlet-heated tubes, were deployed over a 6-month period, with a beta attenuation monitor (BAM) serving as the reference device. The performance of the OPCs using the same inlet tubes for the first 3 months was compared to their performance after the frequent replacement of clean tubes during the final 3 months. The correlation coefficients (r 2) for the 1 h and 24 h average PM2.5 concentrations between the OPCs and the BAM were lower with long-term contaminated tubes (0.82 0.93). The relative mean errors and biases significantly increased over time with contaminated tubes. Temperature, humidity, precipitation, and wind speed were found to have an insignificant effect (r 2 < 0.1) on the performance of the two OPCs with inlet-heated tubes over the 6-month period. The relative average PM2.5 error when using clean tubes was less than 4%. These findings highlight the importance of inlet-heated tubes in improving OPC performance, particularly for mitigating humidity effects. Graphical Abstract

Keywords

• Ambient air
• Beta attenuation
• Optical particle counter
• Cheap sensor
• PM2.5