The chemical composition of indoor air is dynamic; in response to perturbations such as emissions from cooking and cleaning, organic compounds undergo partitioning between the gas phase, the particle phase, and indoor surfaces. The chemical composition, structure, and resulting chemical properties of these compounds play a major role in determining their ultimate fate indoors. The Chemical Assessments of Surfaces and Air (CASA) study at the NIST Net-Zero Energy Residential Test Facility was designed to examine the impacts of these perturbations in an unoccupied single-family home. During CASA, we measured the real-time chemical composition of gas-phase organic compounds using a proton transfer reaction mass spectrometer and performed in situ gas chromatographic separation to speciate isomers. From controlled additions of pure gaseous ammonia to the house (to simulate ammonia emissions from typical indoor activities), we observed exchange of acids and bases between the gas phase, particle phase, and surfaces; basic nitrogen-containing compounds (C2-4H3-5N1O0-2) partitioned off surfaces and entered the gas phase, while small carbon backbone carboxylic acids (e.g., formic and acetic acid) were removed from the gas-phase and partitioned to surfaces and/or indoor aerosols. We also examined the role of ammonia in perturbing gas-phase concentrations from dedicated cooking experiments, for more realistic quantities of ammonia co-emitted to indoor air with a complex mixture of organic compounds. Using gas chromatography, we observed each nitrogen-containing ion signal entering the gas phase to include one to eight chromatographic peaks, showing a rich distribution of both isomeric contributions as well as possible fragments of higher molecular weight nitrogenated species. Extending this gas chromatographic investigation across the entire campaign, during which experiments were performed to simulate a variety of typical indoor activities or outdoor pollution intrusion events, we investigate the contribution of isomers and fragments to commonly reported gas-phase ions in proton transfer reaction mass spectrometry studies.

Role of acids and bases in controlling indoor air composition in an unoccupied test house

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