9614105 Seinfeld The goal of this project is to develop a fundamental understanding of atmospheric nucleation and gas-to-particle conversion processes via an integrated program of laboratory experiments, field measurements, nucleation theory, and atmospheric modeling. Smog chamber experiments will be performed to study the yields of aerosols from the gas-phase photooxidation of hydrocarbons containing roughly seven or more carbon atoms. Some of the oxidation products have sufficiently low vapor pressures to partition between the gas and the condensed phase, forming secondary organic aerosols. Earlier experiments addressed the oxidation of single hydrocarbons in the presence of nitrogen oxides; in this project, complex hydrocarbon mixtures will be investigated. These will be chosen to be representative of the strongly anthropogenically-influenced continental atmosphere as well as the remote, largely biogenically-dominated, continental atmosphere. Experiments and modeling work will be performed in order to better understand binary nucleation of the sulfuric acid/water system, which is regarded as the most important source of new particles in the marine boundary layer, the free troposphere, and the polluted continental atmosphere. The experiments will be conducted in a photochemical reactor with the goal of measuring the rate of nucleation over a range of atmospherically relevant relative humidities. In addition, Monte Carlo simulations of a simple model for ion-induced nucleation will be carried out. A Differential Mobility Analyzer (DMA) for measuring the size distribution of small aerosol particles will be developed whose charging system will be based on a new concept: it will optimize the charging by varying the ion density as the particle size range is scanned by the DMA. It will be possible to apply larger charges for the smaller particles and therefore enhance the counting efficiency for ultrafine particles, allowing detection of particles whose diameter is below 1 nm. Another component of this project is the participation in the North Atlantic Regional Aerosol Characterization Experiment (ACE-2) which will be conducted in June and July, 1997, over the subtropical Northeastern Atlantic Ocean as an international collaborative effort. The main objectives of ACE-2 are to study the properties of atmospheric aerosols relevant to radiative forcing and climate using aircraft, ship-board, and ground-based measurements. Through this grant, the new research aircraft Pelican will be deployed to investigate aerosol properties and their evolution in time. Measurements of aerosol size distributions and other parameters will provide information on possible new particle production and entrainment, processing of anthropogenic aerosol by clouds over the ocean, and the behavior of cloud condensation nuclei in different air masses.
