Laboratory evaluation of hourly mass concentration by PM_2.5 monitors using a mobility particle size spectrometer

The applicability of the mobility particle size spectrometer (MPSS) as a secondary reference for evaluating the accuracy of hourly PM_2.5 mass concentrations measured by automated continuous monitors (ACMs) was investigated under controlled laboratory conditions. Polystyrene and ammonium sulfate aerosols were used as test aerosols. First, MPSS measurements were compared with the primary gravimetric method based on 3-h averages to determine correction factors and measurement uncertainties for the MPSS. Then, corrected MPSS concentrations were used to assess three ACMs: two beta attenuation monitors (BAMs) and one tapered element oscillating microbalance (TEOM) monitor. Two evaluation approaches were used. The first examined trueness and repeatability of hourly concentrations at a constant concentration of 80–100 µg/m³. ACMs generally agreed with MPSS within 10%, though some deviations exceeded MPSS uncertainty (5%). Relative standard deviations were approximately 2% for BAMs and 4–5% for TEOM. The second assessed linearity and time response of hourly concentrations across 10–160 µg/m³, yielding regression slopes within 10% of unity and R² > 0.999 for all ACMs. These results demonstrate that MPSS can serve as a secondary reference for ACM accuracy evaluations in laboratory tests, potentially supplementing costly ambient comparability studies. The capabilities and limitations of MPSS as a mass concentration reference are discussed. Copyright © 2025 American Association for Aerosol Research