HR: 11:35h
AN: A52B-05    [Abstracts]
TI: From molecular clusters to particles of CCN sizes: Effect of variations in galactic cosmic ray flux
AU: * Yu, F
EM: yfq@asrc.cestm.albany.edu
AF: Atmospheric Sciences Research Center, University at Albany, 251 Fuller Road, Albany, NY 12203 United States
AB: Atmospheric aerosols affect the earth's radiation budget directly by scattering solar radiation, and indirectly by serving as cloud condensation nuclei (CCN). Since ions generated by galactic cosmic ray (GCR) appear to play an important role in the formation of aerosols in the atmosphere, it is physically sound that GCR variations as a result of solar activity and Earth's geomagnetic field change may affect nucleation rate, CCN abundance, and hence the global cloud properties and climate. The question to be answered is the magnitude of such an effect. In order to influence cloud properties, the nucleated particles have to grow to the sizes of CCN. Recent field observations indicate that freshly formed particles can grow to the CCN sizes within the day under favorable conditions. The evolution of molecular ion clusters leading to the formation of new particles and the growth of nucleated particles to CCN sizes are simulated with a size and composition resolved aerosol microphysical model. Our kinetic ion-mediated nucleation (IMN) model solves the complex interactions among vapor molecules, ions, and neutral and charged clusters/particles of various sizes. We have improved our earlier version of the IMN model with the newly developed schemes which enable the model to treat the evaporation of neutral/charged clusters explicitly. The effect of recently recognized dipole-charge interaction on ion clustering thermodynamics is included and the schemes to calculate the evaporation coefficients of H2SO4 molecules have been verified against the experimental data. For the growth of nucleated particles, the condensation of low volatile organic species is also included as many observations indicate that organic species may dominate the growth of particles. Our simulated size distributions of neutral, positively and negatively charged, and total particles range from molecular size to several micrometers under the conditions of several recently reported field campaigns are compared to relevant measurements obtained with the Balanced Scanning Mobility Analyzer, the Air Ion Spectrometer, and the Differential Mobility Particle Sizer. We then discuss the effect of ionization rate variations on nucleation rates, the concentration of nucleated particles and particles of CCN sizes under different atmospheric conditions.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0335 Ion chemistry of the atmosphere (2419, 2427)
DE: 2423 Ionization processes (7823)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005