Oxidation of volatile organic compounds by negative air ions

Although negative air ionizers have been used in indoor air cleaning, few studies have been carried out on removal of volatile organic compounds (VOCs) by negative air ions (NAI). 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 humidities 0%, 25% and 70%. NAI was generated by a negative electric discharge at 15.0kV. The reaction chamber was designed as a dark discharge to prevent the generation of O-3 and NOx. NAI concentrations were 1.34 x 10(6)-1.24 x 10(6) ion cm(-3) at relative humidities between 0% and 70%. The results indicate that the order of reactions of chloroform and toluene with NAI was zero, and was 0.433 for 1,5-hexadiene. The reaction rate constants of chloroform, toluene, and 1,5-hexadiene were 1.74-3.07, 1.07-2.66 ppb min(-1) and 0.463-0.478 ppb(0.567) 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. (C) 2004 Elsevier Ltd. All rights reserved.