Performance Evaluation of an Optical Particle Counter in Mexico City

ANIL NAMDEO, Elizabeth Vega, A. Mezza, Ann Wellens, Northumbria University and Particles Plus Inc.

     Abstract Number: 167
     Working Group: Instrumentation and Methods

Abstract
This study reports on an optical particle counter (OPC) performance evaluation against a reference Beta Attenuation Mass (BAM) monitor.

Particles Plus outdoor ambient air monitor, EM10000, is an OPC designed for outdoor particulate monitoring. EM10000 adopts concurrent measurement of multiple, user-selectable PM sizes from 0.3um to 10 µm, including TPM of particles up to 25 µm. It has a closed-loop humidity control for incoming airstream (to provide more accurate particulate sizing) and a closed-loop condensation control within the enclosure.

BAM used for this study is a Thermo Electron Corporation, model FH 62 C-14 Series Particle Monitor, with a source model WA-1186. In BAM, airflow is introduced through a pump that deposits particles on a filter for specific periods.

Both BAM and EM10000 were co-located at Instituto de Ciencias de la Atmósfera, where there is a monitoring site called Ciencias de la Atmósfera, which belongs to the Secretariat of the Environment of Mexico City. The data from co-located BAM and OPC were collected at hourly intervals and used to determine OPC's performance against the reference BAM monitor.

The performance evaluation was based on PM2.5 concentrations from May 2022 to July 2023. When 1-hourly averages were used, the correlation coefficient between BAM and EM10000 was 0.78 and the slope was 1.139 indicating over-estimation by EM10000. When 24-h averages were used the correlation coefficient between BAM and EM10000 was 0.91 and the slope was 1.08 indicating a slight over-estimation by EM10000.

Overall, it can be concluded that the Particles Plus OPC’s performance against a reference BAM monitors was consistent and satisfactory over one year period.