Building disinfection chemistry: heterogeneous consumption of gaseous disinfecting agents and resulting by-product formation
This study focused on the chemistry that occurs during building disinfection using ozone, chlorine dioxide, hydrogen peroxide vapor, and methyl bromide. Experiments were performed in small chambers to determine disinfectant consumption and by-product formation and persistence associated with 24 building materials for each disinfectant. The effect of varied concentration, relative humidity, and ventilation rates were examined. The study involved over 140 experiments (disinfectant/material combinations and parameter variations) and the analysis of over 3,000 samples to identify and quantify by-product formation. The results of this study indicate that there are differences in the extent and nature of interactions between different disinfectants and individual materials, and between individual disinfectants and different materials. The majority of by-products were saturated C1 to C9 carbonyls. Ozone led to the greatest mass of quantified by-products across all test materials, but varied in magnitude and fingerprint (specific carbonyls) between test materials. Long-term by-product persistence was likely for several materials. Chlorine dioxide led to the second greatest mass of quantified by-products. One un-quantified by-product was produced when latex paint was exposed to chlorine dioxide was much larger than any other quantified or non-quantified peak identified in this study. Chlorinated by-products, including 1-chloro-2-propanone, 1,1-dichloro-2- propanone, and methyl dichloroacetate, were identified as by-products for 13 of the 24 materials. Relative to ozone and chlorine dioxide, hydrogen peroxide vapor lead to modest production of by-products. Building disinfection by-product formation and release from materials during experiments was near detection limits for most materials. By-product release factors were generally an order of magnitude less than for ozone, and less than chlorine dioxide, although the by-product release rate was of similar scale. Methyl bromide led to small increases in emissions for some chemicals. In general, these increases were lower than for ozone or chlorine dioxide. This may be due to competitive displacement of chemicals that already existed in the materials, although there was evidence that methylation of materials did occur. There are positive and negative aspects to each of the methods of disinfection examined in this dissertation. The best method of disinfection would vary for different disinfection scenarios and would need to be decided on a case-by-case basis.