N. Montassier

Inspiratory deposition of ultrafine particles in human nasal replicate cast

Abstract The deposition of particles in replicate cast models of the human nasal cavity has been measured in three different laboratories for a range of particle sizes from 0.6 to 200 nm. The results of these measurements on four different casts can be fit by a single equation of the form η=1 − exp [−bQ − 1 8 D 1 2 ], where η is the fraction of particles deposited in the nasal cavity, Q is the volumetric flow rate (1 min−1), D is the particle diffusion coefficient (cm2s−1), and b is found to be 12.65 ± 0.17. The measurements were conducted over a range of flow rates from 1.4 to 28.71 min−1 (501 min−1 for sizes from 4.6 to 200 nm) using radon and thoron decay product aerosols as well as larger ultrafine particles. These results thus represent a current best estimate of the diffusional deposition of ultrafine particles in the human nasal cavity.

A System to Measure the Hygroscopicity of Aerosol Particles

An aerosol conditioner (wetted wall reactor) was modified to mimic the conditions inside the human respiratory tract, i.e., relative humidity > 99% and 37°C. By combining the wetted wall reactory with tandem differential mobility analyzer, a system was developed to study the hygroscopic properties of aerosols in submicrometer range. This paper describes the system, and the results of system tests using three compounds of known composition, NaCl, (NH4)2SO4, and (NH4)HSO4, are presented.

Assessment of the exposure to and dose from radon decay products in normally occupied homes

The exposure to radon decay products has been assessed in seven homes in the northeastern United States and southeastern Canada. In two of the houses, there was a single individual who smoked cigarettes. There were a variety of heating and cooking appliances among these homes. These studies have provide 565 measurements of the activity-weighted size distributions in these houses. The median value for the equilibrium factor was 0.408 as compared with the previously employed value of 0.50. Using the recently adopted ICRP lung deposition and dosimetry model, the hourly equivalent lung dose rate per unit, radon exposure was estimated for each measured size distribution. The mean equivalent dose rate per unit of 222 Rn gas concentration was approximately 140 nSv h -1 Bq -1 m -3 . It was found that the equivalent dose was strongly correlated with the ratio of the decay product concentration to that of radon, termed the equilibrium factor, F, with a correlation coefficient of 0.785. The correlation coefficient with the ≤2-nm size fraction (the «unattached» fraction) was 0.169, reflecting no significant relationship with the unattached fraction. Differences between houses with smokers present and absent were noted in the exposure conditions, but the resulting dose rate per unit of radon gas concentration was essentially the same for the two groups. Expressed in terms of ICRPs unit of effective dose for members of the public, the mean dose rate conversion coefficient with respect to radon gas concentration found in this study was 3.8 nSv h -1 Bq -1 m -3

Evaluation of the effectiveness of several air cleaners for reducing the hazard from indoor radon progeny

In studies conducted in the early 1980s, it was suggested that the use of room-type air cleaners were relatively ineffective in reducing the hazards associated with the presence of radon decay products in indoor air. Some studies suggested that air cleaning could actually increase the dose delivered by the decay products by shifting the activity-weighted particle size distribution to smaller sizes to the point where dose increase even though exposure decreased. A recently developed automated, semicontinuous instrument now permits the direct measurement of activity-weighted size distributions in occupied homes so that the exposure to those occupants can be directly determined and the effect of the air cleaners on dose be estimated. Three different types of air cleaners were tested in this study; an electrostatic air cleaner (EAC), an ion generator / fan system (IG / F), and a filtration unit that was operated at two different fan speeds (LO-FIL and HI-FIL). The three units reduced the median exposure to ra...

Evaluation of several air cleaners for reducing indoor radon progeny

Abstract Over the past several years, studies have been made of the effectiveness of several kinds of air cleaners in removing radon decay products from indoor air using a recently developed automated, semi-continuous measurement system that can determine the activity-weighted size distributions in occupied homes. Measurements of activity-weighted size distributions and radon concentrations were made every 90 min in a home with a high air exchange rate. A week-long series of measurements was made for the home with no cleaner operating and a similar set of measurements were made for each of the air cleaners. Two different types of air cleaners were tested in this study; filtration units (two different designs from two different manufacturers) and two ion generator/fan systems (identical design NO-RAD systems, but from two different manufacturers). From the measured distributions and a dosimetric model, the effect of the air cleaners on the dose to lung can be estimated. It was found that the filtration units resulted in a median reduction in exposure of 15% and 36% for the two units and corresponding dose reductions of 32% and 53%. The two NO-RAD systems produced 37% and 10% reductions in the median exposure, but the reductions in the median dose were 49% and 46%. Examination of the components of the NO-RAD system operating separately resulted in the fan causing a small dose reduction and the ionizer producing a small dose increase. However, very few size distributions were measured for these separate component studies and a more detailed study of the separate effects of the NO-RAD components is needed.

Analysis of the performance of a radon mitigation system based on charcoal beds

Abstract The performance of a commercially available radon mitigation system based on adsorption of radon onto charcoal beds (RAdsorb system) combined with an electronic air cleaner (EAC) installed in a single family house in Massachusetts has been studied. Semi‐continuous measurements were made of the radon gas concentration, potential alpha energy concentration (PAEC), and radon decay product activity‐weighted size distribution with and without additional operating aerosol sources. An automated, semi continuous graded screen array (ASC‐GSA) system was utilized for the measurement of the activity‐weighted size distribution. During the tests without the mitigation system in operation, the conditions in the basement of the house were as follow: the radon concentrations were in the range of 600 to 800 Bq m‐3, the Potential Alpha Energy Concentration (PAEC) was 600 to 700 nJ m‐3, the particle concentration was below 1000 cm‐3, and the fraction of PAEC and 218 Po in the smallest size range, 0.5–1.6 nm were ap...