Development and evaluation of a continuous coarse (PM10-PM2.5) particle monitor

In this paper, we describe the development and laboratory and field evaluat ion of a continuous coarse (2.5-10 mum) particle mass (PM) monitor that can provide reliable measurements of the coarse mass (CM) concentrations in ti me intervals as short as 5-10 min. The operating principle of the monitor i s based on enriching CM concentrations by a factor of similar to 25 by mean s of a 2.5-mum cut point round nozzle virtual impactor while maintaining fi ne mass (FM)-that is, the mass of PM2.5 at ambient concentrations. The aero sol mixture is subsequently drawn through a standard tapered element oscill ating microbalance (TEOM), the response of which is dominated by the contri butions of the CM, due to concentration enrichment. Findings from the field study ascertain that a TEOM coupled with a PM,, inlet followed by a 2.5-mu m cut point round nozzle virtual impactor can be used successfully for cont inuous CM concentration measurements. The average concentration-enriched CM concentrations measured by the TEOM were 26-27 times higher than those mea sured by the time-integrated PM10 samplers [the micro-orifice uniform depos it impactor (MOUDI) and the Partisol] and were highly correlated. CM concen trations measured by the concentration-enriched TEOM were independent of th e ambient FM-to-CM concentration ratio, due to the decrease in ambient coar se particle mass median diameter with an increasing FM-to-CM concentration ratio. Finally, our results illustrate one of the main problems associated with the use of real impactors to sample particles at relative humidity (RH ) values less than 40%. While PM10 concentrations obtained by means of the MOUDI and Partisol were in excellent agreement, CM concentrations measured by the MOUDI were low by 20%, and FM concentrations were high by a factor o f 5, together suggesting particle bounce at low RH.