Intercomparison of activity size distributions of thoron progeny by alpha- and gamma-counting methods.

It is difficult to calibrate sampling devices using radon or thoron progeny or particles measuring 1-4 nm; therefore, an interlaboratory comparison is important to verify the performance of graded diffusion batteries for the activity size distributions of the "unattached" progeny. This paper describes the results of an interlaboratory comparison of 220Rn progeny size distributions using graded diffusion batteries by alpha- and gamma-counting methods with different data inversion schemes. Graded diffusion batteries designed at the Inhalation Toxicology Research Institute and at the Environmental Measurement Laboratory were used in the study. Screens and backup filters from the Environmental Measurement Laboratory-graded diffusion batteries were counted simultaneously in alpha counters for total alpha activities, and those of the Inhalation Toxicology Research Institute-graded diffusion batteries were counted in a gamma detector for gamma activities from 212Pb. Because of the different counting methods and data analysis procedures used, this interlaboratory study of 220Rn progeny allows a more rigorous way of testing instrument performance. 212Pb particles generated in well-controlled environments of oxygen, nitrogen, or oxygen with 1 ppm of nitrogen oxide were measured. In general, good agreement in activity size distributions was obtained from these two methods. Some differences observed in individual size spectra were attributable to the data inversion programs used in each laboratory. When the data were analyzed by the same computer program, most differences disappeared.

The measurement of activity-weighted size distributions of radon progeny: methods and laboratory intercomparison studies.

Over the past 5 y, there have been significant improvements in measurement of activity-weighted size distributions of airborne radon decay products. The modification of screen diffusion batteries to incorporate multiple screens of differing mesh number, called graded screen arrays, have permitted improved size resolution below 10 nm such that the size distributions can now be determined down to molecular sized activities (0.5 nm). In order to ascertain the utility and reliability of such systems, several intercomparison tests have been performed in a 2.4 m3 radon chamber in which particles of varying size have been produced by introducing SO2 and H2O along with the radon to the chamber. In April 1988, intercomparison studies were performed between direct measurements of the activity-weighted size distributions as measured by graded screen arrays and an indirect measurement of the distribution obtained by measuring the number size distribution with a differential mobility analyzer and multiplying by the theoretical attachment rate. Good agreement was obtained in these measurements. A second set of intercomparison studies among a number of groups with graded screen array systems was made in April 1989 with the objective of resolving spectral structure below 10 nm. Again, generally good agreement among the various groups was obtained although some differences were noted. It is thus concluded that such systems can be constructed and can be useful in making routine measurements of activity-weighted size distributions with reasonable confidence in the results obtained.

An evaluation of an ultra-high-volume airborne particulate sampler, the LEAP.

A modified ultra-high-volume liquid electrostatic aerosol precipitator sampler (LEAP) was calibrated with near monodisperse aerosols of water-soluble and insoluble materials in the size range of 0.02 to 4 microns diameter. The water-soluble materials were ammonium sulfate and ammonium hydrogen sulfate. The insoluble materials included carnauba wax, stearic acid, silver chloride and Y(THD)3. The particulate collection efficiency of the unit ranged from 40 to 98%, depending on particle size, sampling air flow and also on particle material. Tests with water-soluble aerosols showed higher collection efficiency than those with the insoluble aerosols by about 2 to 10%. A sharp decline in the collection efficiency for the particles smaller than 0.1 micron was observed. A comparison with the available manufacturer's data for the particle diameters of 0.1 to 3 microns suggests that the manufacturer overestimated the collection efficiency by 6 to 20% for an air flow of 10 m3/min. We consider the LEAP to be a useful ultra-high volume sampler, especially suited for low-level or short-term sampling.

Radon daughter plateout--I. Measurements.

Radon daughter plateout (surface deposition) was measured directly in 1.9 and 20-m3 chambers. To test the effect of different parameters on plateout, measurements were made over a wide range of particle concentrations and sizes. The results indicate that plateout is strongly dependent on particle concentration. The ratio of surface-deposited activity to total daughter activity in the chamber varied from 4% at particle concentrations greater than 10(5)/cm3 to 86% for particle concentrations less than 10(3)/cm3. Comparison for the experimental data with a theoretical model shows that the theory overestimates plateout and underestimates the airborne concentration by factors of about 3.5 and 3.3, respectively.

Generation and characterization of condensation aerosols of benzo[alpha]pyrene.

Condensation aerosols of benzo[a]pyrene (BAP) with particle sizes ranging from 0.1 to 2 micrometers (aerodynamic diameter) were produced and studied. These aerosols were generated in a glove box by direct vaporization of BaP and homogeneous condensation of the vapor. The aerosol concentration ranged from 50 to 700 micrograms/l with aerosol production rates up to 15 mg BaP per minute. The effects of vaporization temperature and flow rate of diluting air on the particle size distribution and aerosol output were studied. The BaP aerosol was produced with relatively constant mass concentration and particle size distribution for more than 5 h. The aerosol was physicochemically and thermally stable. Data on the in vitro dissolution of BaP particles in aqueous solvents and in different dissolution systems suggested that the organic BaP particle does not dissolve in simple aqueous solvents. Proteins, surfactants, or ethyl alcohol enhanced the rate of dissolution of BaP. The rate of dissolution of BaP particles was inversely proportional to particle size.

Distribution, retention, and elimination of pyrene in rats after inhalation.

Pyrene was measured in tissues of Fischer 344 rats are various times after inhalation of pyrene aerosols (500 microgram/l; mass median diameter, 0.3-0., micrometer) for 1 h. Significant quantities of pyrene were found in nasal turbinates, trachea, lungs, kidney, and liver immediately after exposure. Clearance from the respiratory tract was rapid; concentrations in the trachea and lungs 48 h after exposure were 20 and 5% of the concentrations present 1/2 h after exposure. Pyrene also cleared from liver and kidney at a relatively rapid rate; concentrations in these tissues 48 h after exposure were approximately 10% of those 1/2 h after exposure. Concentrations in the gastrointestinal tract 24 h after exposure were 4 times those found 1/2 h after exposure. Pyrene cleared from the gastrointestinal tract approximately 4 d after exposure. Thus, inhaled pyrene is rapidly cleared from the respiratory tract by mucocilliary action from the trachea and bronchi and by translocation from the respiratory tract to the liver and kidney; it is eliminated primarily through the gastrointestinal tract.

Generation and characterization of condensation aerosols of vanadium pentoxide and pyrene.

Generation and characterization of submicron aerosols of V2O5 and pyrene, two materials with very different physicochemical properties, were studied. Vaporization-condensation methods were used to generate the aerosols. The effects of various experimental conditions on particle size and aerosol mass concentration were investigated. Also, chemical stability of the aerosols and the source materials with respect to temperature was determined. Experimental results show that there are significant differences in the nature of pyrene and V2O5 aerosols. These methods and experimental conditions can be easily adapted for generation of heterogeneous condensation aerosols of pyrene and V2O5.