A molecular picture of surface interactions of organic compounds on prevalent indoor surfaces: limonene adsorption on SiO₂

Abstract

Integration of experiment, theory and modeling to understand the interaction type and kinetics of limonene on silica surfaces.

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

“…Note that the chemical interactions with the sur-face reservoirs may not be fully captured by the conventional measures of partitioning, specifically the K oa and K wa values. As one example, in the case of limonene, strong hydrogen bonding occurs to glass surfaces (9). These interactions are not included by the two conventional partitioning parameters used here.…”

The atmospheric chemistry of indoor environments

“…For example, limonene binds strongly to silica with an adsorption enthalpy of À55 kJ mol À1 , but the desorption timescale for individual molecules is calculated to nevertheless be on the order of 10's of microseconds. 152 The diffusion timescales of sorbed molecules deep within a building material may be longer. For example, paint can be formulated to be sufficiently porous to permit air exchange with the interior spaces in the walls and ceilings.…”

“…With the enormous heterogeneity of indoor spaces, indoor chemistry models have to be tested against measurements in a wide range of environments, to assess the degree to which their predictions are quantitatively accurate and transferable. A modeling consortium has been formed with a hierarchical approach to the development of indoor modeling, 4 an approach that is already providing insights into fundamental interactions of gases with building materials 152,260 and the heterogeneous chemistry that occurs when ozone interacts with within skin oils and clothing. 204,205 This approach is required because detailed processes at the molecular level can not be directly incorporated into models that capture air motions using computational uid dynamics.…”

Indoor boundary layer chemistry modeling

“…While the uptake coefficient would be 0 in the absence of surface reactions, a terpene may react with oxidants at the surface, such as O 3 and OH, leading to a non‐zero uptake coefficient for that terpene. For example, it is known that terpenes will sorb to surfaces and react heterogeneously with ozone on model surfaces and on indoor surfaces . Based on this literature, the uptake coefficient for limonene is estimated to be quite small (See Appendix S1: Discussion in S.8); however, there may be other surface/terpene/oxidant systems that result in higher effective uptake coefficient for a volatile terpene like limonene.…”