Control of Volatile Organic Compounds, Particulates, and Bioaerosols with the Aid of Negative Air Ions in Indoor Environment
Date Issued
2006
Date
2006
Author(s)
Wu, Chih-Cheng
DOI
zh-TW
Abstract
This study investigated the control of volatile organic compounds (VOCs), particles, and bioaerosols with the aid of negative air ions (NAIs) in indoor environment. The NAIs were generated by negative electric discharge; the discharge was kept at less than 0.01 mA and 30.0 kV. The reaction chamber was designed as a dark discharge to prevent the generation of O3 and NOx. This study investigated the concentration gradient of NAI at various temperatures, relative humidities and distances in indoor air, and developed an empirical model for concentration gradient of NAI as well. Experimental results indicate that the concentration gradient of NAI was little affected by temperatures between 23.9C and 25.7C. However, the influence of relative humidity on the concentration gradient of NAI was complicated. There were four trends for the relationship between NAI concentration and relative humidity at different distances from the discharge electrode. Additionally, the regression analysis of NAI concentrations and distances from the discharge electrode indicated a logarithmic linear (log-linear) relationship; the distance of log-linear tendency decreased with an increase in relative humidity. Moreover, an empirical model for the concentration gradient of NAI generated in indoor air was developed for estimating the NAI concentration.
This study investigated the reactions of NAI and VOCs in a batch reactor. Three species of VOCs - chloroform, toluene and 1,5-hexadiene - were selected to react with NAI at relative humidity of 0, 25 and 70%. The NAI was generated by a negative electric discharge at 15.0 kV. The NAI concentrations were 1.34E6 to 1.24E6 ion cm-3 at relative humidities between 0 and 70%. The results indicate that the order of the reactions of chloroform and toluene with NAI was zero, and 0.433 order for 1,5-hexadiene. The reaction rate constants of chloroform, toluene and 1,5-hexadiene were 1.74 - 3.07 ppb min-1, 1.07 - 2.66 ppb min-1 and 0.463 - 0.478 ppb0.567 min-1 at relative humidity from 0 to 70%. The effect of relative humidity on the reaction kinetics was obvious for chloroform and toluene but not for 1,5-hexadiene. The reaction between 1,5-hexadiene and NAI generated a relatively stable intermediate species, 4-pentenal. The oxidation of chloroform, toluene and 1,5-hexadiene by NAI proceeded slowly.
This study investigated the control of particles with the aid of NAIs in an indoor environment. The results indicated that the PM2.5 and submicron particle were obviously removed by NAIs. Moreover, this work studied how wall surface materials influence the removal of airborne particles with NAIs. Five wall surface materials – stainless steel, wood, PVC (polyvinyl chloride), wallpaper and cement paint – were applied to the inner surface of a test chamber. The results indicated that NAI could remove particles from the wood and PVC wall surfaces substantially more effectively than from other wall materials. The various electrical characteristics and roughness of the wall materials may have been responsible for the associated of the various ECRs (effective cleaning rate) with the various wall surface materials.
Although negative air ionizers have been used in indoor air cleaning, little study have been done on the elimination of bioaerosols by NAIs. This study investigated the removal and germicidal effects of NAIs on bioaerosols. Bioaerosols, Escherichia coli (E. coli), Bacillus subtilis (B. subtilis) endospores, spores of Penicillium citrinum (P. citrinum), and yeast cells of Candida famata (C. famata) var. flareri, were produced by six-jet Collison nebulizer, which aerosolized the suspension of microorganisms in DI water and PBS (phosphate buffer solution). NAIs were generated at a concentration of 5E5 ions cm-3 in an experimental chamber (9.32E-2 m3) by negative electric discharge at 10 kV. The removal and germicidal efficiencies of bioaerosols were measured by aerodynamic particle sizer (APS) and high velocity impinger (AGI-30), respectively. Bioaerosols collected by AGI-30 was cultured for colony forming unit (CFU) counting. The results indicated that the removal efficiency of bioaerosols was enhanced by NAIs and increased with the retention time of bioaerosol in the experimental chamber. The germicidal efficiency of bioaerosols was evaluated by the survival factor (SF). The SF less than 1 and approach of 1, respectively, showed that the NAIs with and without germicidal efficiency of bioaerosols. The results indicated that the SF was 0.96 +- 0.19 at different retention time and relative humidity, therefore, the germicidal function of NAIs on bioaerosols was invalid. However, the removal effect of NAIs on bioaerosols was the major mechanism for eliminating the bioaerosols using negative air ionizers.
Subjects
空氣負離子
負極針尖放電
揮發性有機污染物
懸浮微粒
生物氣膠
Negative air ions
Negative electric discharge
Volatile organic compounds
Particle
Bioaerosol
Type
thesis
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