Research Projects: Current laboratory studies

We use our fixed-temperature, fixed-volume 7.5 m3 Teflon chamber to probe how oxidative "aging" affects the amounts and chemical composition of atmospheric organic aerosol. A particular focus of our work is the isolation of a single phase in which multigenerational aging occurs (in the gas phase, in aqueous aerosol, etc.), requiring the development of novel approaches for generating high level of oxidants within a given phase.

The direct climate impacts - the absorption and scattering of light - of black carbon (soot) particles are thought to be impacted by atmospheric processing, though this is highly uncertain at present. Using flow-tube and chamber techniques to age black carbon (via heterogeneous oxidation and/or the addition of secondary aerosol coatings), combined with state-of-the-art measurements of the chemical and optical properties of the particles, we hope to better understand how the climate-relevant properties of these particles evolve during their atmospheric lifetimes.

While organic compounds with high vapor pressures (VOCs) and those with low vapor pressures (organic aerosol) are now routinely measured in lab and field studies, gas-phase organic compounds with vapor pressures between the two extremes (semivolatile organic compunds and intermediate-volatility organic compounds) generally are not. Thus we have developed a new mass spectrometric instrument for quantifying and chemically characterizing such species as an ensemble.

In collaboration with Kevin Wilson (Lawrence Berkeley National Laboratory) and Doug Worsnop (Aerodyne Research) we carry out flow-tube studies aimed at understanding the oxidation of particle-phase organic compounds by gas-phase OH radicals. A major focus is how chemical structure and degree of oxidation influences whether an organic molecule will undergo functionalization (which generally lowers its vapor pressure) or fragmentation (which generally increases it).

In this project we study the formation of secondary organic aerosol (SOA) via the direct generation of key radical intermediate species. Alkoxy radicals and alkylperoxy radicals are generated from the photolysis of precursors (alkyl nitrites and alkyl iodides, respectively), and particle-phase products of their reactions are examined using aerosol mass spectrometry. The advantage of this approach is that individual reaction pathways and oxidation generations can be probed, which is not possible in standard hydrocarbon + oxidant studies.