The partitioning of low-and semi-volatile organic compounds into and out of particles significantly influences secondary organic aerosol formation and evolution. Most atmospheric models treat partitioning as an equilibrium between gas and particle phases, despite few direct measurements and a large range of uncertain mass accommodation coefficients (α). Here we directly measure the dynamic, isothermal partitioning of specific organic compounds using mass spectrometry in a Teflon chamber. Measurements are conducted under dry and humid conditions using seeds of different properties that are atmospherically relevant. α values determined independently from gas-and particle-phase observations are consistent and average 0.88 ± 0.33 for all the studied seeds and probe gases. Our results also imply fast mixing, within~200 s, between dry α-pinene/O 3 SOA and the oxidized compounds. These results indicate that mass transfer limitations in the atmosphere may be less important than some recent studies suggest.

Humans spend approximately 90% of their time indoors, impacting their own air quality through occupancy and activities. Human VOC emissions indoors from exercise are still relatively uncertain, and questions remain about emissions from chlorine‐based cleaners. To investigate these and other issues, the ATHLETic center study of Indoor Chemistry (ATHLETIC) campaign was conducted in the weight room of the Dal Ward Athletic Center at the University of Colorado Boulder. Using a Vocus Proton‐Transfer‐Reaction Time‐of‐Flight Mass Spectrometer (Vocus PTR‐TOF), an Aerodyne Gas Chromatograph (GC), an Iodide‐Chemical Ionization Time‐of‐Flight Mass Spectrometer (I‐CIMS), and Picarro cavity ringdown spectrometers, we alternated measurements between the weight room and supply air, allowing for determination of VOC, NH3, H2O, and CO2 emission rates per person (emission factors). Human‐derived emission factors were higher than previous studies of measuring indoor air quality in rooms with individuals at rest and correlated with increased CO2 emission factors. Emission factors from personal care products (PCPs) were consistent with previous studies and typically decreased throughout the day. In addition, N‐chloraldimines were observed in the gas phase after the exercise equipment was cleaned with a dichlor solution. The chloraldimines likely originated from reactions of free amino acids with HOCl on gym surfaces.

Understanding the sources and composition of organic aerosol (OA) in indoor environments requires rapid measurements, since many emissions and processes have short timescales. However, real‐time molecular‐level OA measurements have not been reported indoors. Here, we present quantitative measurements, at a time resolution of five seconds, of molecular ions corresponding to diverse aerosol‐phase species, by applying extractive electrospray ionization mass spectrometry (EESI‐MS) to indoor air analysis for the first time, as part of the highly instrumented HOMEChem field study. We demonstrate how the complex spectra of EESI‐MS are screened in order to extract chemical information and investigate the possibility of interference from gas‐phase semivolatile species. During experiments that simulated the Thanksgiving US holiday meal preparation, EESI‐MS quantified multiple species, including fatty acids, carbohydrates, siloxanes, and phthalates. Intercomparisons with Aerosol Mass Spectrometer (AMS) and Scanning Mobility Particle Sizer suggest that EESI‐MS quantified a large fraction of OA. Comparisons with FIGAERO‐CIMS shows similar signal levels and good correlation, with a range of 100 for the relative sensitivities. Comparisons with SV‐TAG for phthalates and with SV‐TAG and AMS for total siloxanes also show strong correlation. EESI‐MS observations can be used with gas‐phase measurements to identify co‐emitted gas‐ and aerosol‐phase species, and this is demonstrated using complementary gas‐phase PTR‐MS observations.