The House Observations of Microbial and Environmental Chemistry (HOMEChem) study was a large-scale collaborative experimental investigation probing indoor air composition and chemistry.
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 cleaningseveral
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.
It
is important to improve our understanding of exposure to particulate
matter (PM) in residences because of associated health risks. The
HOMEChem campaign was conducted to investigate indoor chemistry in
a manufactured test house during prescribed everyday activities, such
as cooking, cleaning, and opening doors and windows. This paper focuses
on measured size distributions of PM (0.001–20 μm), along
with estimated exposures and respiratory-tract deposition. Number
concentrations were highest for sub-10 nm particles during cooking
using a propane-fueled stovetop. During some cooking activities, calculated
PM2.5 mass concentrations (assuming a density of 1 g cm–3) exceeded 250 μg m–3, and
exposure during the postcooking decay phase exceeded that of the cooking
period itself. The modeled PM respiratory deposition for an adult
residing in the test house kitchen for 12 h varied from 7 μg
on a day with no indoor activities to 68 μg during a simulated
day (including breakfast, lunch, and dinner preparation interspersed
by cleaning activities) and rose to 149 μg during a simulated
Thanksgiving day.
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