Organic compounds suspended in the gas- and particle-phases are emitted into indoor environments from a wide range of sources, including cooking, cleaning, personal care products, natural and manufactured building materials, and even occupants themselves. These emissions are often present in high concentrations, and can be transformed through complex oxidation chemistry. These compounds and their oxidation products impact concentrations of indoor oxidants (e.g. ozone), may contribute substantially to adverse health effects through direct toxicity, and can form harmful particulate matter.
A typical sample of ambient air contains thousands or tens of thousands of organic compounds, and nearly all processes acting on suspended organic carbon depend on its chemical structures and properties. Chemical reaction rates, oxidation products, and condensation onto surfaces and suspended particles are all impacted by the specific structures and chemical functional groups present in a molecule. Consequently, the fate of indoor organic compounds – whether they are deposited to indoor surfaces, react with indoor oxidants, or survive long enough to be removed to the outdoors – depends critically on the molecular structures and chemical functional groups of indoor organic carbon. Measurements of individual known molecules with sufficient structural detail can be measured in this mixture by field-deployable gas chromatographs (GC), but these known compounds represent only a small fraction of organic carbon. A more comprehensive characterization is available using the current generation of field-deployable direct chemical ionization mass spectrometers (CIMS), which enable the characterization of large fractions of atmospheric OC by molecular formula, but provide little molecular specificity or resolution of isomers; for example, hydroxyacetone and propionic acid are both measured as C3H6O2 despite differing by a factor of several in reactivity, vapor pressure, acidity, etc., and orders of magnitude in instrument sensitivity. The current lack of methods for the chemical resolution and characterization of individual unidentified compounds consequently substantially impedes our understanding of indoor chemical processes.
The primary goal of this project is: to couple gas chromatography and chemical ionization mass spectrometry (GC-CIMS) to provide resolution of isomers with different chemical functionalities alongside characterization of unknown compounds, and to measure isomer-resolved emissions from occupants of buildings to better understand humans as a ubiquitous and highly variable indoor emissions source.
Expected outcomes of this research are:
- Improved understanding of the composition and chemical processes in indoor atmospheres. The proposed instrument will separate isomers by molecular structure and characterize them by their molecular formula alongside quantification of known compounds, a significant advance over current tools for the measurement of specific molecules, which provide little information about unknown compounds.
- Characterization and calibration of other deployed instrumentation. Multiple CIMS instruments have seen widespread recent and upcoming applications in indoor environments, but the calibration and interpretation of their data remains a substantial challenge due to the lack of information they provide about the molecular structures of observed analytes. The proposed instrument will characterize the effects of molecular structure on CIMS instrument response, and, if possible, identify approaches for correcting or improving current calibration approaches.
- New insights into the impacts of occupants on indoor environments. Emissions from humans and personal care products have a major impact on indoor atmospheres. However, characterization and composition of human emission rates are limited. Proposed measurements will yield significant new insight into humans as a source of emissions and the environmental conditions that control them.
PI: Gabriel Isaacman-VanWertz (Virginia Tech)
Co-PI: Farrokh Jazizadeh Karimi (Virginia Tech)
Collaborating business partner: Aerodyne Research Inc. (Billerica, MA), primary investigators: Manjula Canagaratna, Brian Lerner
Collaborators: John Little (Virginia Tech), Brent Stephens (Illinois Institute of Technology)