Armin Wisthaler

Reactions of ozone with human skin lipids: Sources of carbonyls, dicarbonyls, and hydroxycarbonyls in indoor air

This study has used proton transfer reaction-mass spectrometry (PTR-MS) for direct air analyses of volatile products resulting from the reactions of ozone with human skin lipids. An initial series of small-scale in vitro and in vivo experiments were followed by experiments conducted with human subjects in a simulated office. The latter were conducted using realistic ozone mixing ratios (≈15 ppb with occupants present). Detected products included mono- and bifunctional compounds that contain carbonyl, carboxyl, or α-hydroxy ketone groups. Among these, three previously unreported dicarbonyls have been identified, and two previously unreported α-hydroxy ketones have been tentatively identified. The compounds detected in this study (excepting acetone) have been overlooked in surveys of indoor pollutants, reflecting the limitations of the analytical methods routinely used to monitor indoor air. The results are fully consistent with the Criegee mechanism for ozone reacting with squalene, the single most abundant unsaturated constituent of skin lipids, and several unsaturated fatty acid moieties in their free or esterified forms. Quantitative product analysis confirms that squalene is the major scavenger of ozone at the interface between room air and the human envelope. Reactions between ozone and human skin lipids reduce the mixing ratio of ozone in indoor air, but concomitantly increase the mixing ratios of volatile products and, presumably, skin surface concentrations of less volatile products. Some of the volatile products, especially the dicarbonyls, may be respiratory irritants. Some of the less volatile products may be skin irritants.

Development of a Proton-Transfer Reaction-Linear Ion Trap Mass Spectrometer for Quantitative Determination of Volatile Organic Compounds

Currently, proton-transfer reaction mass spectrometry (PTR-MS) allows for quantitative determination of volatile organic compounds in real time at concentrations in the low ppt range, but cannot differentiate isomers or isobaric molecules, using the conventional quadrupole mass filter. Here we pursue the application of linear quadrupole ion trap (LIT) mass spectrometry in combination with proton-transfer reaction chemical ionization to provide the advantages of specificity from MS/MS. A commercial PTR-MS platform composed of a quadrupole mass filter with the addition of end cap electrodes enabled the mass filter to operate as a linear ion trap. The rf drive electronics were adapted to enable the application of dipolar excitation to opposing rods, for collision-induced dissociation (CID) of trapped ions. This adaptation enabled ion isolation, ion activation, and mass analysis. The utility of the PTR-LIT was demonstrated by distinguishing between the isomeric isoprene oxidation pair, methyl vinyl ketone (MVK) and methacrolein (MACR). The CID voltage was adjusted to maximize the m/ z 41 to 43 fragment ratio of MACR while still maintaining adequate sensitivity. Linear calibration curves for MVK and MACR fragments at m/ z 41 and 43 were obtained with limits of detection of approximately 100 ppt, which should enable ambient measurements. Finally, the PTR-LIT method was compared to an established GC/MS method by quantifying MVK and MACR production during a smog chamber isoprene-NO x irradiation experiment.

Desiccant wheels as gas-phase absorption (GPA) air cleaners: evaluation by PTR-MS and sensory assessment

UNLABELLED Two experiments were conducted to investigate the use of the co-sorption effect of a desiccant wheel for improving indoor air quality. One experiment was conducted in a climate chamber to investigate the co-sorption effect of a desiccant wheel on the chemical removal of indoor air pollutants; another experiment was conducted in an office room to investigate the resulting effect on perceived air quality. A dehumidifier with a silica-gel desiccant wheel was installed in the ventilation system of the test chamber and office room to treat the recirculation airflow. Human subjects, flooring materials and four pure chemicals (formaldehyde, ethanol, toluene and 1,2-dichloroethane) were used as air pollution sources. Proton-Transfer-Reaction--Mass Spectrometry (PTR-MS) and sensory subjects were used to characterize the effectiveness of chemical and sensory pollution removal of the desiccant wheel. The experiments revealed that all the measured VOCs were removed effectively by the desiccant wheel with an average efficiency of 94% or higher; more than 80% of the sensory pollution load was removed and the percentage dissatisfied with the air quality decreased from 70% to 20%. These results indicate that incorporating a regenerative desiccant wheel in a ventilation system is an efficient way of removing indoor VOCs. PRACTICAL IMPLICATIONS This study may lead to the development of new air cleaners and validates a new concept for the design of ventilation systems that can improve indoor air quality and reduce energy consumption.