Rainer's general interest is the study of atmospheric chemistry in air quality and climate science, using a combination of in-situ and remote sensing measurement techniques, which he and his group are developing and deploying in polluted urban and pristine atmospheric environments from ships, research aircrafts, and autonomous ground-based networks, and in simulation chamber experiments to develop and test the mechanistic understanding represented in atmospheric models used to manage air resources and climate.
Atmospheric waters: multiphase chemistry in clouds and aerosols
Water is a major metastable component of the lower atmosphere (see photo) and present at most atmospheric interfaces, including aerosols. We are interested in understanding the multiphase chemistry of glyoxal, an unexplained component in arctic, marine, forest, and urban aerosols, and its indicator properties to understand phase partitioning and chemical processes in aerosol water. Multiphase chemistry in aqueous aerosols is largely missing in atmospheric models for lack of data, missing information about precursors and reaction pathways, and difficulties with assessing contributions from multiphase chemistry to ambient secondary organic aerosol mass. The effective Henry's law coefficient, KH, describes the partitioning of a molecule between the condensed water phase and the gas phase in the limit of infinite dilution. KH also determines the reaction rates of multiphase chemical reactions in the bulk of aerosols ('A'in figure) and clouds. We have determined KH,salt for the first time by time-resolved measurements of gas-phase and particle-phase glyoxal concentrations in sulfate-containing aerosols. From the exponential increase in KH,Salt over that in pure water, we determine the Setschenow salting constant of glyoxal, KSCHOCHO. This is the first determination of KS in a dynamically coupled gas-aerosol system ('B' in figure). We find that aqueous ammonium sulfate (AS) and internally mixed ammonium sulfate/fulvic acid (AS/FA) aerosols both show an exponential increase of KH,Salt with AS concentration (Kampf et al. 2013). Activity coefficients of approximately 1/500 are caused by electrical forces in aerosol water due to a "salting-in" mechanism (Kampf et al. 2013) and help explain field measurements in Mexico City (Waxman et al. 2013). Salting constants provide a framework that is novel in atmospheric models, yet may prove critical with predicting multiphase chemistry of other polar molecules in the atmosphere. References Kampf, CJ, EM Waxman, JG Slowik, J Dommen, A Prevot, U Baltensperger, T Hoffmann, and R Volkamer. 2013. Effective Henry's law partitioning and the salting constant of glyoxal in aerosols containing sulfate. Environ. Sci. Technol. 47(9):4236– 4244. Waxman, EM, K Dzepina, B Ervens, R Volkamer, et al. 2013. Secondary organic aerosol formation from semi- and intermediatevolatility organic compounds and glyoxal: relevance of O/C as a tracer for aqueous multiphase chemistry. 2013. Geophys. Res. Lett. 40:978-982.
Honors and Awards
- NSF CAREER Award recipient, 2009
- Feodor-Lynen Fellow (2005-2007)
- Henry & Camille Dreyfus Fellow (2002-2004)
- Marie Curie Fellow (1998-2000)
- Erasmus Fellow (1992-1993)