Secondary Organic Aerosols

Atmospheric aerosols are presently poorly understood in terms of their sources, formation, and climate forcings.  They have multiple effects on climate change (primary light scattering and secondary cloud-condensation properties) and respiratory health.  Secondary organic aerosols (SOA) have undergone an explosion in research activity, due to the recent discovery of oligomeric compounds resulting from the heterogeneous reactions of volatile organic compound (VOC) oxidation products.  Previously, the SOA was thought to arise entirely by simple gas-particle partitioning of VOCs.

As part of an EPA STAR grant , our research is geared to improve our quantitative and mechanistic understanding of the mechanisms for secondary organic aerosol from the atmospheric oxidation of α- and β-pinene.  This involves determining product yields for major gas phase OH- and O3-induced oxidation products with much smaller uncertainty bounds.  We are presently studying the oligomerization of aerosol phase species and the extent to which photochemistry and acid-catalyzed chemistry in aerosols and in cloud water contributes to secondary organic aerosol production. 

Our approach involves a unique combination of laboratory photochemical reaction chamber studies and field measurements of the pinene reaction products and aerosol growth above forest environments.  We possess an extensive array of state of the art analytical and experimental resources, including:

• The highly powerful Desorption-ElectroSpray-Ionization (DESI)-MS technique for analysis of aerosol-phase organics from filter samples, cascade impactor plates, and cloud water samples.  This is in collaboration with R. Graham Cooks’ Aston Laboratory for Mass Spectrometry .

• A Scanning Mobility Particle Sizer (SMPS) spectrometer for determining aerosol yield, size distribution, and particulate evolution over time.  This was used recently in the PROPHET 2008 Summer campaign [link to Nate’s page].
• An all-Teflon photochemical reaction chamber .
• A newly developed and highly powerful instrument called a Proton Transfer Reaction Linear Ion Trap (PTR-LIT ) for identification and quantitation of VOCs and oxygenated VOCs.
• The Shepson group Airborne Laboratory for Atmospheric Research (ALAR ) aircraft for sampling cloud water.
• The Total Reactive Nitrogen Instrument for determining gas phase concentrations of NOy classes, allowing for the determination of gas-aerosol partitioning.
• A GC×GC-ECD for quantitative characterization of specific organonitrate species.  GC×GC also enables the determination of an unknown’s polarity and volatility.

• A suite of other instruments for intercomparison purposes, such as a GC-FID, a NOx analyzer, an ozone analyzer, and autosampling-GC-MS.