Formation and emission of hydrogen chloride in indoor air

To improve our understanding of chlorine chemistry indoors, reactive chlorine species such as hydrogen chloride ( HC l) must be analyzed using fast time‐response measurement techniques. Although well studied outdoors, sources of HC l indoors are unknown. In this study, mixing ratios of gaseous HC l were measured at 0.5 Hz in the indoor environment using a cavity ring‐down spectroscopy ( CRDS ) instrument. The CRDS measurement rate provides a major advance in observational capability compared to other established techniques. Measurements of HC l were performed during three types of household activities: (a) floor exposure to bleach, (b) chlorinated and nonchlorinated detergent use in household dishwashers, and (c) cooking events. Surface application of bleach resulted in a reproducible increase of 0.1 ppbv in the affected room. Emissions of HC l from automated dishwashers were observed only when chlorinated detergents were used, with additional HC l emitted during the drying cycle. Increased mixing ratios of HC l were also observed during meal preparation on an electric element stovetop. These observations of HC l derived from household activities indicate either direct emission or secondary production of HC l via chlorine atoms is possible. Calculations of photolysis rate constants of chlorine atom precursors provide evidence that photolysis may contribute to indoor HC l levels.