A.V. Nero

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.

Potable water as a source of airborne 222Rn in U. S. dwellings: a review and assessment

Using a long-term-average, single-cell model and available data for U.S. housing, the concentration of 222Rn in indoor air due to the use of potable water is assessed. The ratio of the airborne 222Rn concentration to the concentration in water is represented by a lognormal distribution with geometric mean and geometric standard deviation of 0.65 X 10(-4) and 2.88, respectively, in fair agreement with the previously reported results of direct measurements of the ratio in 13 houses. By combining this result with data on 222Rn concentrations in U.S. water supplies, potable water is estimated to contribute an average of 24, 1.3, and 0.1 Bq m-3 to the airborne 222Rn concentration in residences served by private wells, public ground water, and surface water supplies, respectively.

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.

Time-averaged indoor Rn concentrations and infiltration rates sampled in four U.S. cities

Indoor Rn concentrations, measured in 58 houses during a 4- to 5-mon period during the winter and spring of 1981-1982, varied from 0.1-16 pCi l-1 (4-590 Bq m-3). Average infiltration rates were determined for each house during the same period, based on a measurement of the effective leakage area and an infiltration model, and found to range from 0.2-2.2 air changes per hour (h-1). Indoor Rn concentrations correlated poorly with infiltration rates for houses within each city as well as for the entire sample. Differences in Rn entry rates among houses thus appear to be more important than differences in infiltration rates in determining whether a house has high indoor Rn levels, consistent with previous indications from grab-sample measurements. Radon entry rates and indoor Rn concentrations were generally higher in houses in Fargo, ND, and Colorado Springs, CO, than in houses in Portland, ME, and Charleston, NC.

HUMAN DISEASE FROM RADON EXPOSURES: THE IMPACT OF ENERGY CONSERVATION IN RESIDENTIAL BUILDINGS

Abstract The level of radon and its daughters inside conventional buildings is often higher than the ambient background level. Interest in conserving energy is motivating home-owners and builders to reduce ventilation and hence to increase the concentration of indoor generated air contaminants, including radon. It is possible that the current radiation levels in conventional homes and buildings from radon daughters could account for a significant portion of the lung cancer rate in non-smokers. Moreover, it is likely that some increased lung cancer risk would result from increased radon exposures; hence, it is prudent not to allow radon concentrations to rise significantly. There are several ways to implement energy conservation measures without increasing risks.

Dependence of indoor-pollutant concentrations on sources, ventilation rates, and other removal factors

The behavior of several classes of chemical and physical pollutants include emissions from combustion appliances, radon and its progeny, formaldehyde, and other organic compounds. Current research at Lawrence Berkeley Laboratory is described and research needs in the area of indoor air quality is pointed out. (ACR)