HR: 08:45h
AN: A41B-03    [PDF]
TI: Preparation And Characterization Of Organic Coatings Of Variable Thickness On Inert Cores And Their Chemical Reactions With Ozone
AU: Katrib-Kouchnir, Y
EM: ykatrib@deas.harvard.edu
AF: Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AU: * Martin, S T
EM: smartin@deas.harvard.edu
AF: Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AU: Rudich, Y
EM: Yinon.Rudich@weizmann.ac.il
AF: Weizmann Institute, Dept.of Environmental Sciences, Rehovot, 76100 Israel
AU: Zhang, H
EM: zhanghd@bc.edu
AF: Boston College, Dept.of Chemistry, Chestnut Hill, MA 02467 United States
AU: Davidovits, P
EM: paul.davidovits@bc.edu
AF: Boston College, Dept.of Chemistry, Chestnut Hill, MA 02467 United States
AU: Jayne, J T
EM: jayne@aerodyne.com
AF: Aerodyne Research, Inc, 45 Manning Road, Billerica, MA 08121-3976 United States
AU: Worsnop, D R
EM: worsnop@aerodyne.com
AF: Aerodyne Research, Inc, 45 Manning Road, Billerica, MA 08121-3976 United States
AB: Recent studies have emphasized the role of organic atmospheric particles in cloud formation, radiative forcing, and health effects. Quantification of these effects is limited because the compositions, morphologies, and chemical reactivities of organic particles are poorly understood. Laboratory studies are motivated to understand and quantify complex particles and their processes. A critical unknown is the heterogeneous chemistry that depends upon and leads to changes in the morphological and chemical complexity of the particles. Our work is focused on ozone heterogeneous chemistry as a general proxy for understanding the role of layer thickness and diffusivity in chemical transformations of surface and interior layers of complex particles. Our approach for preparing the particles is as follows. Polystyrene latex (PSL) particles are atomized into an aerosol flow. Oleic acid particles are formed by vapor condensation from a separate flow through a heated liquid reservoir. When the flows are mixed, the PSL and oleic acid particles are externally mixed. An oven having a linear hot-to-cold temperature gradient is employed to first evaporate the oleic acid particles in the hot region, which is followed by condensation in the cold region onto the surface of the PSL particles acting as heterogeneous nuclei. Internally mixed particles result. The apparatus capability is the controlled and reproducible generation of particles having 2 to 30 nm surface layers of oleic acid and 100 nm polystyrene latex (PSL) cores. The temperature of the reservoir, the gradient of the furnace, and the adjustable flow are the levers controlling the layer thickness of oleic acid. The particles are characterized in parallel by their electric mobility in a TSI Scanning Mobility Particle Sizer (SMPS) and their aerodynamic diameter in an Aerodyne Aerosol Mass Spectrometer (AMS). Diameter and oleic acid coating mass agree well by the two methods. The particle shape factor is approximately unity, indicating spherical particles. Chemical reactivity of the particles with ozone at 0 and 85% relative humidity (RH) is studied. Changes in particle diameter are studied by SMPS and AMS. Loss of parent oleic acid is observed in the mass spectrum collected by the AMS. These factors are studied as a function of oleic acid layer thickness. Results of these measurements will be presented.
DE: 0305 Aerosols and particles (0345, 4801)
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting