Patrick J. Feeney

Analysis of respirable fractions in atmospheric particulates via sequential filtration

It has long been recognized that information on particle size distributions in atmospheric aerosals is necessary for meaningful evaluations of potential health hazards. Such information is also important in establishing particulate sources, transport, transformations, and sinks, especially in combination with elemental and chemical data. While instruments exist to collect size segregated samples of particulates, they are too complex and expensive to encourage use of multiple units in field situations.

Characterization of particles in the arid west

Abstract This paper describes spatial and temporal variations of airborne paniculate matter in the eight western states included in the western fine particle network (WFPN). The samples were generated by a 40-site monitoring network of remotely sited dichotomous samplers of the stacked filter and virtual design, with a coarse fraction between 15 μm and 2.5 μm dia. and a fine fraction below 2.5 μm dia. The units operate for two 72 h period each week, delivering samples analyzed gravimetrically for mass and by particle induced X-ray emission (PIXE) for elements sodium and heavier. Results are presented for the period October 1979 to May 1980, showing regional patterns of particles especially in the fine modes. A sulfur episode which occurred in the southwest is examined via trajectory analysis, while factor analysis is applied to the entire data set to generate information on particulate sources.

Sensitivity versus target backings for elemental analysis by alpha excited X-ray emission

Abstract The sensitivity of elemental analysis by charged-particle induced X-ray fluorescence is examined by measuring characteristic X-ray cross sections for K α , K β , L α , L β , L γ , and M transitions for many elements and bremsstrahlung backgrounds from thin mylar, kapton, and teflon films between 0.7 and 8 mg/cm 2 thickness. Sensitivities are given as a function of target atomic number, backing thickness, incident beam charge, energy and flux, and detector configuration. An evaluation of the strengths and weaknesses of charged-particle induced X-ray emission for elemental analysis is included.

Particulate monitoring at US National Parks using PIXE

Abstract In order to help the United States National Park Service understand the causes of visibility impairment at various national parks throughout the United States, the Crocker Nuclear Laboratory at the University of California, Davis, has been collecting samples of coarse and fine particles at 35 sites continuously since 1982. At these remote sites most visibility impairment is due to the scattering of light by fine particles, between 0.2 and 1 μm. We are responsible for all aspects of the monitoring program, including designing and maintaining the particulate samplers, handling and analyzing the filters, and presenting and interpreting the results. A successful monitoring program requires strict adherence to carefully prepared procedures at all stages, with numerous quality assurance checks. All the samples are analyzed for mass by microbalance and for elemental composition by PIXE. PIXE is well-suited to particulate monitoring in terms of accuracy, cost, range of elements, and spatial resolution. The concentration of fine hydrogen is measured by proton elastic scattering operated simultaneously with the PIXE analysis. We also measure the optical absorption by fine soot particles using the integrating plate method. Because the sites arc remote and the sampling is almost continuous, most of the measured variables show well-defined regional patterns when averaged over the seasons of the year. The wide range of elements permits a good characterization of the fine particles. There are wide differences in the overall composition for different regions. In the eastern US the fine mass is dominated by ammonium sulfate. In some regions of the western US, fine soil and organics are important components to the aerosol. For visibility, fine sulphur is the most single important element measureable by PIXE. For most regions sulfur is largest in summer, although in some regions the maxima are in spring or fall. The average sulfur concentration varies widely over the US. with values in the east ten times those in some regions of the west. The concentrations of other variables, such as potassium, lead, zinc, copper, hydrogen, silicon are also important in understanding the composition of fine particles.

Complete elemental analysis of aerosols: PIXE, FAST, LIPM, and mass☆

Abstract Methods are described that allow additional information to be gained on aerosol parameters from samples suitable for PIXE analysis. In particular, these methods yield ways to directly compare the sum of all elemental species with total mass obtained by weighing or β gauging the same sample.

Size-time composition profile of aerosols using the drum sampler

Abstract Mie scattering theory imposes strict requirements for both size and compositional information on aerosols associated with visibility degradation. But, at the very clean National Park Service sites where we do such studies, episodes of degraded visibility may be infrequent and of short duration. To meet these needs, an 8 stage impactor of the Battelle/SFU design was mated to rotating drum impaction surfaces of the Lundgren design in a compact and rugged DRUM sampler of Davis design. This unit, three years in development, has been extensively tested using laboratory aerosols and field intercomparisons. The standard unit runs essentially unattended for 14 or 28 days. The samples are analyzed in 2 to 8 hour time segments. Analyses are done by carefully collimated (1 mm, 2 mm) proton beams in a tightly coupled PIXE system, yielding sensitivities of a few solng m 3 . Dramatic shifts in the size distribution of sulfur versus time have been observed, with direct influence on optical extinction. Further, primary smelter effluents have been clearly identified at Grand Canyon NP, but only in the

Gravimetric determination of mass on lightly loaded membrane filters

The paper discusses procedures used to obtain mass data on particulates from more than 25,000 membrane filters in an air quality study of 40 remote areas of the United States. Results show that a large number of particulate samples can be analyzed for mass by weighing, with excellent precision and accuracy without a significant increase in sample handling time. Use of an electrobalance has the added advantage of being relatively inexpensive, with values independent of filter orientation, laboratory atmospheric conditions, and the elemental makeup of the particles and the filter substrates. Careful control of electrostatic effects must be maintained, however, and strict adherence to formal quality assurance protocols is essential.

Effect of Roadbed Configuration on Traffic Derived Aerosols

Aerosols present upwind and downwind of freeways in the Los Angeles Basin were collected in five particle size ranges by Lundgren impactors with after filters and analyzed for elemental content by ion-excited x-ray emission. The contribution of freeway traffic to total airborne particulate load was obtained by subtracting the local background, measured by an upwind sampler, from the values obtained by downwind samplers on a size by size, element by element basis. This contribution correlated reasonably well with estimates derived from automotive and roadbed expendable rates. Traffic-derived aerosols, normalized to vehicular flow, were considerably lower in mass downwind of depressed roadbed configurations than either at grade or raised configurations. A line source model, combined with literature values for emitted lead, produced good agreement with results obtained in the at grade configuration.

Comparison of equal-velocity ion beams for elemental analysis by ion-excited X-ray emission

Abstract Detectable limits for elemental analyses using protons and alpha particles with a velocity of 4 MeV/amu proved to be essentially the same.

On background subtraction in PIXE analysis of aerosol samples

Abstract The technique of background evaluation by using the spectrum of a blank substrate can, in principle, only be applied to spectra of lightly loaded aerosol samples with substrates having the same thickness as the blank. In this paper we present and discuss experimental results to show the effects of thickness difference between the blank and the sample substrate on such background evaluation. Computational procedures for making corrections for these effects as well as for the effects of thick sample mass are suggested.