| Abstract: |
In this project, we plan to investigate the relationships between the chemical composition of organic particles (as represented by the specific functional groups that are present) and the hygroscopicity and CCN activity of SOA formed from the oxidation of the major classes of anthropogenic and biogenic volatile organic compounds (VOCs) that are emitted to the atmosphere, as well as model hydrocarbons. The specific objectives are as follows: (1) characterize the chemical composition of SOA formed from the oxidation of model hydrocarbons and anthropogenic and biogenic hydrocarbons, (2) evaluate the hygroscopicity and CCN activity of SOA formed from the oxidation of model hydrocarbons, (3) evaluate the hygroscopicity and CCN activity of SOA formed from the oxidation of anthropogenic and biogenic hydrocarbons, and (4) develop parameterizations relating hygroscopicity and CCN activity to organic composition and sources.
The general experimental approach for this project will involve the use of large-volume environmental chambers to generate SOA from reactions of VOCs with the major atmospheric oxidants: OH and NO3 radicals and O3. A subset of these experiments will also be performed in a smaller, steady-state, continuous-flow reaction chamber. The instruments and methods to be used for aerosol chemical analysis include: a thermal desorption particle beam mass spectrometer, a variety of chromatographic separation methods, and spectrophotometry and Fourier transform infrared analysis of functional groups. These chemical analyses will be complemented by characterization of particle hygroscopicity above and below water saturation. In the subsaturated regime, equilibrium aerosol water content as a function of relative humidity (RH) will be measured via a humidified tandem differential mobility analyzer (HTDMA), while CCN activity will be measured for atmospherically-relevant critical supersaturations using a condensation nucleus counter (CCNc). From the results of these studies, we will develop parameterizations relating organic aerosol chemical properties and SOA sources to particle hygroscopicity and CCN activity for use in atmospheric models. |
