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

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-HRToF-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 nonpolar organic gases, indoor WSOG loss rate coefficients were substantial for compounds with high oxygen-to-carbon (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 h−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.