Multiphase Chemistry Controls Inorganic Chlorinated and Nitrogenated Compounds in Indoor Air during Bleach Cleaning

Abstract

We report elevated levels of gaseous inorganic chlorinated and nitrogenated compounds in indoor air while cleaning with a commercial bleach solution during the House Observations of Microbial and Environmental Chemistry field campaign in summer 2018. Hypochlorous acid (HOCl), chlorine (Cl2), and nitryl chloride (ClNO2) reached part-per-billion by volume levels indoors during bleach cleaningseveral orders of magnitude higher than typically measured in the outdoor atmosphere. Kinetic modeling revealed that multiphase chemistry plays a central role in controlling indoor chlorine and reactive nitrogen chemistry during these periods. Cl2 production occurred via heterogeneous reactions of HOCl on indoor surfaces. ClNO2 and chloramine (NH2Cl, NHCl2, NCl3) production occurred in the applied bleach via aqueous reactions involving nitrite (NO2 –) and ammonia (NH3), respectively. Aqueous-phase and surface chemistry resulted in elevated levels of gas-phase nitrogen dioxide (NO2). We predict hydroxyl (OH) and chlorine (Cl) radical production during these periods (106 and 107 molecules cm–3 s–1, respectively) driven by HOCl and Cl2 photolysis. Ventilation and photolysis accounted for <50% and <0.1% total loss of bleach-related compounds from indoor air, respectively; we conclude that uptake to indoor surfaces is an important additional loss process. Indoor HOCl and nitrogen trichloride (NCl3) mixing ratios during bleach cleaning reported herein are likely detrimental to human health.

Indoor Surface Chemistry: Developing a Molecular Picture of Reactions on Indoor Interfaces

“…100 For example, from this combination of the state-of-the-art measurements with kinetic modeling, it was revealed that multiphase chemistry drives inorganic chlorinated and nitrogenated compounds in indoor air during bleach cleaning. 67 Overall, as greater emphasis is placed on understanding the surface as an active participant in indoor chemistry, and not simply as an unknown entity that is a host to multiphase chemistry, the overall understanding of the chemistry of indoor environments and impacts on human health will improve. Central to improving the understanding of reactions occurring at surfaces are efforts to characterize the surfaces being probed, the use of standard surfaces across different indoor experiments to provide intercomparability and the understanding of the factors that drive surface chemistry.…”

“…These HOCl-dominated formation pathways become far more important indoors than outdoors and have been shown to impact the overall indoor oxidant budgets. 66 , 67 These halogen oxidants subsequently react with organic films 68 and with VOCs to form aerosols that provide further surface area for indoor reactions. 69 For example, HOCl can react with unsaturated molecules to form chlorohydrins ( Equation 5 ).…”

“… 100 For example, from this combination of the state-of-the-art measurements with kinetic modeling, it was revealed that multiphase chemistry drives inorganic chlorinated and nitrogenated compounds in indoor air during bleach cleaning. 67

Figure 3 Conceptual Schematic of Recommended Approach to Indoor Surface Studies

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How human biology and behavior affect indoor air quality

“…House cleaning is a pollution culprit as well. When using a commercial bleach solution, the researchers measured new ultrafine (<100 nm in diameter) particle formation and elevated levels of chlorine-containing gases (6). "This is evidence that there are chemical transformations occurring on quite rapid timescales in the indoor environment," says Farmer.…”

Development of a personal passive air sampler for estimating exposure to effective chlorine while using chlorine‐based disinfectants

“…Two important effective chlorine species from bleach are chlorine (Cl 2 ) and hypochlorous acid (HOCl); recent studies have reported that concentrations of both these gases in indoor air significantly increased while using commercial bleach, with concentrations of Cl 2 and HOCl reaching 20‐25 and 50‐250 of ppbv, respectively 6,7 . Acute inhalation of these gases generally causes health problems such as reactive airways dysfunction syndrome (RADS) owing to Cl 2 gas generation from bleach use, especially when bleach mixes with acidic solutions such as hydrochloric acid (HCl) and vinegar 8‐10 .…”