Dynamics of Residential Water-Soluble Organic Gases: Insights into Sources and Sinks

Abstract

Water-soluble organic gas (WSOG) concentrations are elevated in homes. However, WSOG sources, sinks, and concentration dynamics are poorly understood. We observed substantial variations in 23 residential indoor WSOG concentrations measured in real time in a North Carolina, U.S. home over several days with a high-resolution time-of-flight chemical ionization mass spectrometer equipped with iodide reagent ion chemistry (I-HR-ToF-CIMS). Concentrations of acetic, formic, and lactic acids ranged from 30-130, 15-53, and 2.5-360 μg m −3 , respectively. Concentrations of several WSOGs, including acetic and formic acids, decreased considerably (~ 30-50%) when the air conditioner (AC) cycled on, suggesting that the AC system is an important sink for indoor WSOGs. In contrast to non-polar organic gases, indoor WSOG loss rate coefficients were substantial for compounds with high O:C ratios (e.g., 1.6-2.2 h −1 for compounds with O:C > 0.75 when the AC system was off). Loss rate coefficients in the AC system were more uncertain, but were estimated to be 1.5 hr −1. Elevated concentrations of lactic acid coincided with increased human occupancy and cooking. We report several WSOGs emitted from cooking and cleaning as well as transported in from outdoors. In addition to indoor air chemistry, these results have implications to exposure and human health.

Overview of HOMEChem: House Observations of Microbial and Environmental Chemistry

“…Organic acids are prominent in the outdoor atmosphere, 30,77,78 but also have indoor sources, including human metabolism, building materials, and oxidation chemistry. [79][80][81] Exchange of indoor and outdoor air means that outdoor sources may contribute to indoor air organic acid concentrations. Fig.…”

“…This calculation assumes indoor-to-outdoor transport was 100% efficient, although water soluble oxygenated VOCs can be lost to indoor surfaces. 81 A test house-equivalent area of managed lawn soil would be expected to emit $6 Â 10 À5 mol h À1 of formic acid and 3-5 Â 10 À4 mol h À1 of acetic acid. 85 Residential homes may therefore be a stronger source of formic acid to outdoor urban atmospheres than area-equivalent emissions from soil.…”

The atmospheric chemistry of indoor environments

“…This effect has been demonstrated by measurements of the temporal behavior of water-soluble organic gases, such as formic and acetic acid, whose gas-phase mixing ratios decreased when air conditioning cycled on. 149 Partitioning timescales. The diffusion times for molecules through thin surface lms are fast, i.e.…”

Surface reservoirs dominate dynamic gas-surface partitioning of many indoor air constituents

“…We note that condensed-phase water may modulate these interactions by competing for adsorption sites or by changing species diffusivity in organic matrices (12). In addition, there is the potential for sorbed molecules to partition to a water-rich phase present on surfaces, to water sorbed in different building materials (e.g., hydrated gypsum in wallboard), or even to bulk water present, e.g., in kitchens and bathrooms (13).…”