Michael P. Tolocka

Technical Note: Performance of a Personal Electrostatic Precipitator Particle Sampler

Filter-based methodsused to measure aerosols with semi-volatile constituents are subject to biases from adsorption andvolatilization that may occur during sampling(McDowandHuntzicker 1990; Turpin and Huntzicker 1994; Volckens et al.1999; Tolocka et al. 2001). The development and evaluation ofsuitable methods for quantitative measurement of semivolatileorganic aerosols is of public health signi” cance because thisclass of chemicals can include polycyclic aromatic hydrocar-bons, pesticides, and many other known toxins(Harkov 1986;Finlayson-Pitts and Pitts 1999). Furthermore, the need existsfor personal exposure measurements, since microenvironmen-taloroutdoorsurrogateshavebeenshowntohavelimitedutility(Wallace 1996; Rodes et al. 1991). Previous laboratory and” eld studies have demonstrated that electrostatic precipitationmay be an effective means for sampling such aerosols(Leithet al. 1996; Volckens et al. 1999, 2000). However, samplesof semivolatile aerosols collected by electrostatic precipitators(ESPs)aresusceptibletoreactionsanddegradationduetoozonegenerated by the corona(Kaupp and Umlauf 1992).Although

On the modification of the low flow-rate PM10 dichotomous sampler inlet

A popular flat-topped inlet used for the collection of atmospheric particulate matter was modified to reduce water intrusion during rain and snow events. Simple alterations in the intake region of this inlet were made, including a larger drain hole, a one piece top plate, and louvers. Wind tunnel tests were performed at 24 km/h for fine particle aspiration and at 2, 8, and 24 km/h for coarse particle sampling characteristics of the modified design. The laboratory evaluations of this inlet for fine (PM2.5) and coarse (PM10) particle sampling demonstrated that the aspiration characteristics of this inlet were identical to those of the original inlet. This inlet should greatly reduce, if not totally prevent, the intrusion of precipitation. Further, sampling effectiveness test results suggest that the modified inlet could be substituted for the original inlet where the original inlet is part of a designated reference or equivalent method sampler for PM10.

Characterization of Short-Term Particulate Matter Events by Real-Time Single Particle Mass Spectrometry

Single particle measurements were made in Baltimore, Maryland from March to December 2002 using a real-time single particle mass spectrometer, RSMS-3. Particle composition classes were identified that indicated how the aerosol composition changed with time. The results were compared with collocated instruments giving particle number concentrations and size distributions, sulfate, nitrate, organic, and elemental carbon mass concentrations and total mass. Examination of these measurements revealed several particulate matter (PM) events in which the 24 h averaged PM 2.5 mass exceeded 30 μ g/m 3 . Three of these events were studied in further detail by comparing number and mass concentrations obtained by RSMS-3 with standard methods. For all three events, the number concentrations obtained with RSMS-3 and a scanning mobility particle sizer were highly correlated (R 2 ∼ 0.7). For the event characterized by a high sulfate mass concentration, the RSMS-3 provided an accurate measure of time-dependent nitrate and carbon mass concentrations, but not for sulfate and total mass. For the two events characterized by high carbon mass concentrations (one from a transcontinental wildfire and the other from stagnation during a period of high traffic), RSMS-3 provided an accurate measure of time-dependent nitrate mass, carbon mass and total mass when the aerosol was not dominated by particles outside the size limit of RSMS-3. While the time dependencies were strongly correlated, the absolute mass or number concentrations determined by RSMS-3 were sometimes off by a constant value, which permitted the relative detection efficiencies of some particle classes to be estimated. Other factors that inhibit reconciliation of mass- and number- based concentration measurements are discussed including the difficulty of detecting ammonium sulfate by laser ablation/ionization and the varying size ranges of different particle measurement methods.