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

Abstract

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.

The atmospheric chemistry of indoor environments

“…The temporal responses of gas-phase species to enhancedventilation (usually by opening doors and windows) within genuine indoor spaces have also been monitored. 21,144,145 Gasphase mixing ratios of most gas phase species (i.e. VOCs, HONO, NH 3 ) drop signicantly upon enhanced ventilation because the outdoor air is typically cleaner than that indoors, and the mixing ratios then rebound to their previous steady state values upon closing the doors and windows.…”

“…In another example, repeated enhancedventilation experiments in a house demonstrated this rebound effect on each experiment. 145 This indicates that the surface reservoirs are large, with much more material sorbed to these reservoirs than in the gas phase.…”

“…The model assumes simultaneous equilibria between the gas phase and specied volumes of two surface reservoirs, one polar and one weakly polar. 145,161 Non-reactive interactions involving Fig. 4 Mass loadings for different aerosol particle components in a university building impacted by third-hand smoke (THS), which is seen to have much a higher indoor/outdoor ratio than all other components.…”

“…The same model has been applied to understand observations of gas-surface partitioning in a house. 145 when the uptake coefficient is low, the surface chemistry is ratelimiting and v D scales linearly with g.…”

Indoor Surface Chemistry: Developing a Molecular Picture of Reactions on Indoor Interfaces

“…A second factor that is distinct for indoor environments is the higher concentrations of organic compounds (OCs) across a range of volatility. 19 These high concentrations lead to different partitioning between gases, particles, and surfaces, 20 with more volatile species partitioning to the condensed phase (i.e., surfaces) indoors than in the ambient atmosphere. In addition to the higher concentrations of OCs, including volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs), the surfaces they are interacting with are complex and ever changing.…”