Aerosol Mass Spectrometric Characterization of Ambient Particles: New Techniques and Field Results

Prof. Jose-Luis Jimenez
Dept. Chemistry and Biochemistry and CIRES
University of Colorado-Boulder

Aerosols (small particles suspended in air) play major roles in climate forcing and the hydrological cycle, and also on human health effects, visibility degradation, and deposition of acids, toxics, and nutrients to ecosystems. Organic compounds account for a large fraction (~40%) of ambient submicron aerosol mass, but their sources and transformation processes are poorly understood. The Aerodyne Aerosol Mass Spectrometers (AMS) have emerged as powerful tools for the characterization of organic aerosols due to their sensitivity, speed, and quantitative ability.

Recent AMS developments from our group will be summarized, including the determination of O/C elemental ratios for organic aerosols, eddy-covariance aerosol flux measurements, the first aircraft deployment of the high-resolution AMS (HR-ToF-AMS), the determination of composition-resolved volatility, two new spectral component analysis techniques for AMS spectra, and an intercomparison with the PILS-WSOC technique. Results from several recent field campaigns will be presented, including SOAR-1 in Riverside, MCMA-2003 and MILAGRO in Mexico City, the FLAME biomass burning campaign, and INTEX-B in Seattle.

Secondary organic aerosols (SOA) from anthropogenic precursors are greatly underestimated by current SOA models in Mexico City, as are total organic aerosols by global models (GEOS-Chem and MOZART) in Asian pollution inflow. Real-world SOA is more oxygenated that SOA formed in chambers and is much less volatile than current models assume, while both urban POA and biomass burning OA are much more volatile than real-world SOA. This is consistent with the recently proposed Robinson et al. (Science, 2007) pathway leading to increased SOA, which reduces the discrepancy between SOA models and observations in Mexico City. Oxygenated organic aerosols (OOA) are water-soluble at high dilution but not very hygroscopic.

Wednesday October 17th 2007 at 11 am.
Center Green Laboratory Bldg. 1, South Auditorium
Tea and coffee served before the seminar