A comparison of two direct-reading aerosol monitors with the federal reference method for PM2.5 in indoor air

Two types of direct-reading aerosol monitoring devices, the TSI, Inc. Model 3320 Aerodynamic Particle Sizer (APS), and the TSI, Inc. Model 8520 DustTrak Aerosol Monitor (DustTrak), were collocated indoors with a US EPA designated Federal Reference Method (FRM) PM2.5 sampler, the BGI, Inc. PQ200, to assess the comparability of the sampling methods. Simultaneous 24-h samples were collected from two APS instruments, one DustTrak and one FRM sampler for 20 sample periods. The 30-min average concentrations during the 24-hour sample periods were also logged and compared for the APS and DustTrak. Statistical analysis on the mass concentrations obtained from each sampler type included paired t-tests and linear regression. The 24-h average PM2.5 levels from the FRM samplers were approximately normally distributed and ranged from 5.0 to 20.4 μg m−3 with mean and standard deviation 11.4 and 4.0 μg m−3, respectively. The 24-h average DustTrak levels are well correlated with FRM levels (R2=0.859) but show significant proportional bias (β1=2.57, p<0.0001). The 24-h average mean collocated APS levels are less highly correlated with the FRM (R2=0.592) and do not show statistically significant proportional bias. The 30-min average levels between the two APS instruments show a high correlation (R2=0.979) but significant proportional bias (β1=1.31, p<0.0001). The results suggest that though the DustTrak provides precise measurements of PM2.5, the accuracy of the measurements compared to the FRM can be improved through statistical adjustment. In contrast, APS PM2.5 measurements are less precise and less accurate compared to the FRM and therefore results from the APS should be interpreted with caution.