Unexplored aspects of unipolar ionizer characteristics in context of indoor air cleaning.

Indoor air pollution affects human health via acute and chronic exposure. Traditionally, filter systems have been used for indoor air cleaning; however, issues like filter life and routine maintenance remain associated with their operation. Ionizers are emerging as a potential candidate for indoor air cleaning. A major part of previous studies intended to "project ionizers as air cleaners" focus on particle removal in different conditions. But indices representing charge effects have not been given due attention. This study focuses on the measurement of spatial profile of ion concentration and aerosol current around a single ionizer and a circular array of five ionizers. The distribution of ion concentration around the system/array was found to be isotropic in the absence of ventilation. Aerosol current values under ionizer action have been measured for the first time. Results obtained from this work could be instrumental for the design of future ionizer systems with improved efficacy.

Ionizer induced 220Rn decay product removal in confined environment: Continuous vs. instantaneous source.

This paper presents an experimental approach to evaluate the effectiveness of unipolar ionizers in indoor environment for the removal of thoron (220Rn) daughter products. Both continuous and instantaneous source conditions were simulated during these experiments. Activity and aerosol related parameters were measured for these experiments and results were interpreted. Activity concentration was found to be reduced by a factor 6.6 and 34 for continuous and instantaneous source conditions, respectively. The particle size dependency of mitigation of particles using ionizer is also discussed. The effect of ionizer on activity size distribution has been directly measured for the first time. The ionizer induced changes in particle size distributions were coupled to Dose Reduction Factor (DRF) model and significant DRF values were obtained for both source conditions. This study discusses open issues which are important for establishing ionizer induced radioactivity mitigation as a technology application.

Estimating back to front ratio of wire screen for measurement of thoron decay products.

Wire screens are widely used for measuring the fine fraction of radon/thoron decay products. Their capture efficiencies are generally defined at low aerosol concentration conditions as well as at low sampling flow rates. Effect of changes in sampling flow rate and aerosol concentration on wire screen capture efficiencies and counting correction factor has been studied in this work. Controlled experiments have been conducted using two different mesh sizes at two different aerosol concentration conditions. Experimental results were compared with the existing theories for capture efficiencies of wire screens given by Cheng and Yeh (1980) and Alonso et al. (2001); and semi empirical relation for the front to total ratio given by Solomon and Ren (1992). Theoretical predictions have been found to be relatively close to the experimental findings for moderate aerosol conditions but disagreement was observed in case of high aerosol concentration. The possible reasons for these differences have been discussed in this work.