The House Observations of Microbial and Environmental Chemistry (HOMEChem) study was a large-scale collaborative experimental investigation probing indoor air composition and chemistry.

Human health is affected by indoor air quality. One distinctive aspect of the indoor environment is its very large surface area that acts as a poorly characterized sink and source of gas-phase chemicals. In this work, air-surface interactions of 19 common indoor air contaminants with diverse properties and sources were monitored in a house using fast-response, on-line mass spectrometric and spectroscopic methods. Enhanced-ventilation experiments demonstrate that most of the contaminants reside in the surface reservoirs and not, as expected, in the gas phase. They participate in rapid air-surface partitioning that is much faster than air exchange. Phase distribution calculations are consistent with the observations when assuming simultaneous equilibria between air and large weakly polar and polar absorptive surface reservoirs, with acid-base dissociation in the polar reservoir. Chemical exposure assessments must account for the finding that contaminants that are fully volatile under outdoor air conditions instead behave as semivolatile compounds indoors.

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Author contributions MGDB, PCD and RK conceived and designed the study. MGDB, JFRC, HSP, JH, RR, OLB, MJB, LCP, AN, HC collected the samples and metadata. AB acquired LC-MS data. LIM led LC-MS data analysis. CC led taxonomy and metadata analysis. QZ led DNA data and multi-omics analysis. JJM performed qPCR. SJS, ME, HC, AN, AB, JJM provided additional contributions to data analysis. LIM