K.L. Revzan

Control of Respirable Particles in Indoor Air with Portable Air Cleaners

Abstract Eleven portable air cleaning devices have been evaluated for control of indoor concentrations of respirable particles using in situ chamber decay tests. Following injection of cigarette smoke in a room-size chamber, decay rates for particle concentrations were obtained for total number concentration and for number concentration by particle size with and without air cleaner operation. The size distribution of the tobacco smoke particles was log normal with a count median diameter of 0.15 μm and a geometric standard deviation of 2.0. Without air cleaner operation, the natural mass-averaged surface deposition rate of particles was observed to be 0.1 h −1 . Air cleaning rates for particles were found to be negligible for several small panel-filter devices, a residential-sized ion-generator, and a pair of mixing fans. Electrostatic precipitators and extended surface filters removed particles at substantial rates, and a HEPA-type filter was most efficient air cleaner studied.

Radon transport into a detached one-story house with a basement

We describe the results of a five-month study during which 222Rn (radon) concentration, air- exchange (or ventilation) rate, and weather and radon source parameters were continuously monitored in a house near Chicago, with a view to accounting for the radon entry rate. The results suggest that the basement sump and perimeter drain-tile system played an important role in influencing the radon entry rate and that pressure-driven flow was more important than diffusion as a mechanism for radon entry. For the first 15 weeks of the study period the mean indoor radon concentration and air-exchange rate were 2.6pCil−1 (96 Bq m−3) and 0.22h−1, respectively; both parameters varied over a wide range. Radon concentration measured at the sump cover varied bimodally between 0 and 10 pCil−1 (0–400 Bqm−3) and 300–700 pCil−1 (10,000–30,000 Bq m−3). These two modes corresponded well to periods of low and high indoor radon concentration; average indoor concentrations for these periods were 1.5 and 6.5 pCil−1 (55 and 240 Bq m−3), respectively. For data sorted into two groups according to radon activity at the sump, the indoor radon concentration showed little dependence on air-exchange rate. This result is accounted for by a model in which the radon entry rate, determined by mass balance, has two components—one diffusive, the other a pressure-driven flow component which is presumed to be proportional to the air-exchange rate. In fitting this model to the data we found that (1) the flow component dominated the diffusive component for periods of both high and low activity at the sump and (2) the magnitude of the diffusive component agreed well with the expected contributions of radon emanating from concrete and soil and diffusing into the house. To account for the flow component, we hypothesize that pressure drives air carrying a high concentration of radon generated in the soil, either through the bulk of the soil or along the outside of the basement walls, then into the basement through cracks and openings. During the final six weeks of the study, measurements were made with the water level in the sump maintained first below, then above the entrance of the pipe connected to the perimeter drain tile system. Average indoor radon concentrations during these two periods were 10.6 and 3.5 pCil−1 (390 and 130 Bq m−3), respectively. The relatively high latter value compared with the mean for the first 15 weeks, combined with the observation of intervals of high airborne alpha activity at the sump during this period, suggest that the level of water in the sump does not, by itself, account for the variation in alpha activity at the sump that we had previously observed. Fireplace operation substantially increased the air-exchange rate, but had only a small effect on indoor radon concentration, providing corroborative evidence that pressure-driven flow is an important mechanism for radon entry into this house.

Evaluation of indoor aerosol control devices and their effects on radon progeny concentrations

Abstract Eleven portable air cleaning devices have been evaluated for control of indoor concentrations of respirable particles, and their concomitant effects on radon progeny concentrations have been investigated. The experiments were conducted in a room-size chamber using cigarette smoke and radon injection from an external source. Of the devices examined the electrostatic precipitators and extended surface filters had significant particle removal rates, while the particle removal rates for several small panel-filters, an ion generator, and a pair of mixing fans were found to be essentially negligible. The evaluation of radon progeny control produced similar results; the air cleaners that were effective in removing particles were also effective in reducing radon progeny concentrations. At the low particle concentrations, deposition of the unattached radon progeny on room surfaces was found to be a significant removal mechanism. Deposition rates of attached and unattached progeny have been estimated from these data, and were used to calculate the equilibrium factors for total and unattached progeny concentrations as a function of particle concentration. While particle removal reduces total airborne radon progeny concentrations, the relative alpha decay dose to the lungs appears to change little as the particle concentration decreases due to the greater radiological importance of unattached progeny.

Characterizing the sources, range, and environmental influences of radon 222 and its decay products

Recent results from our group directly assist efforts to identify and control excessive concentrations of radon 222 and its decay products in residential environments. We have demonstrated directly the importance of pressure-induced flow of soil gas for transport of radon from the ground into houses. Analysis of available information from measurements of concentrations in U.S. homes has resulted in a quantitative appreciation of the distribution of indoor levels, including the degree of dependence on geographic location. Experiments on the effectiveness of air cleaning devices for removal of particles and radon decay products indicate the potential and limitations of this approach to control.

A RAPID SPECTROSCOPIC TECHNIQUE FOR DETERMINING THE POTENTIAL ALPHA ENERGY CONCENTRATION OF RADON DECAY PRODUCTS

We consider the application of alpha-spectroscopy to the rapid determination of the potential alpha-energy concentration (PAEC) of radon decay products indoors. Two count totals are obtained after a single counting period. The PAEC is then estimated by a linear combination of the count totals, the two coefficients being determined by analysis of the dependence of the statistical and procedural errors on the equilibrium conditions and the sampling, delay and counting times. For a total measurement time of 11 min, the procedural error is unlikely to exceed 20% for equilibrium conditions commonly found indoors; the statistical error is less than 20% at a PAEC of 0.005 WL, assuming a product of detector efficiency and flow rate of at least 1.0 l./min. An analysis is made of techniques based on a total alpha count, and the results are compared with those obtained with the rapid spectroscopic technique; the latter is clearly preferable when the measurement time does not exceed 15 min.