Estimation of particle mass concentration in ambient air using a particle counter

Particle count may have advantage over particle mass concentration for assessing the health effects of airborne particulate matter. However, health effects have mainly been investigated with mass-measuring instruments, so it is important to assess relationships between the variability of particle number, as determined by an optical particle counter, and the variability of particle mass as measured by traditional mass-measuring instruments. We used a light scattering particle counter to monitor the concentration of particulate matter in ambient air in a northern Italian city continuously from August 2005 to July 2006. Six channels were calibrated to count particles in the size range 0.3–10 μm and above. Particles under 0.3 μm cannot be detected by the instrument. The particle counter was placed alongside the mass-measuring instruments of the Environmental Protection Agency of the Region of Piemonte (ARPA). Particle numbers were transformed into masses and compared with PM10 and PM2.5 data obtained from the ARPA instruments. Daily average values were compared. The correlation between the two methods was good for both PM10 (R2 = 0.734) and PM2.5 (R2 = 0.856); differences between means were significant only for PM2.5. These findings suggest that a light scattering particle counter might be suitable for assessing particulate matter variability in epidemiological studies on effects of air pollution, though further investigations are necessary.