HR: 0800h
AN: A21C-0757    [Abstracts]
TI: Aerosol size distribution in the tropical/subtropical upper tropsophere: First observation of in-situ new particle formation in cirrus clouds
AU: * Lee, S
EM: ShanLee@du.edu
AF: U. Denver, 2399 S York St., Denver, CO 80208 United States
AU: Wilson, J C
AF: U. Denver, 2399 S York St., Denver, CO 80208 United States
AU: Baumgardner, D
AF: Droplet Measurement Technologies, 2400 Central Ave, Boulder, CO 80301 United States
AU: Baumgardner, D
AF: Universidad Nacional Autonoma de Mexico, Centro de Ciencias de la Atmosfera, Circuito Exterior s/n, Ciudad Universitaria, Mexico City, Mex 04510 Mexico
AU: Herman, R L
AF: JPL Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109 United States
AU: Weinstock, E M
AF: Harvard University, 29 Oxford St. , Cambridge, MA 02138 United States
AU: LaFleur, B G
AF: U. Denver, 2399 S York St., Denver, CO 80208 United States
AU: LaFleur, B G
AF: NOAA Climate Modeling and Diagnostics Laboratory, Boulder, CO and University of Colorado, CIRES, 350 S Broadway, Boulder, CO 80301 United States
AU: Kok, G
AF: NASA Langley Research Center, Chemistry and Dynamics Branch, Hampton, VA 23681 United States
AU: Anderson, B
AF: NASA Langley Research Center, Chemistry and Dynamics Branch, Hampton, VA 23681 United States
AU: Lawson, P
AF: SPEC Inc., 3022 Sterling Circle, Suite 200, Boulder, CO 80301 United States
AU: Baker, B
AF: SPEC Inc., 3022 Sterling Circle, Suite 200, Boulder, CO 80301 United States
AU: Strawa, A
AF: NASA, Ames Research Center, Moffett field, CA 94035 United States
AU: Pittman, J V
AF: NASA, Ames Research Center, Moffett field, CA 94035 United States
AU: Reeves, J M
AF: U. Denver, 2399 S York St., Denver, CO 80208 United States
AU: Bui, T P
AF: SPEC Inc., 3022 Sterling Circle, Suite 200, Boulder, CO 80301 United States
AB: Particle nucleation (formation of solid or liquid particles directly from the gas phase) in the upper troposphere and lower stratosphere is an important step in the chain of events that produce clouds, but the mechanisms are poorly understood. Previous studies show that new particle formation takes place in the outflows of marine stratus and cumulus clouds, because cloud scavenging leads to a reduction in the surface area of pre-existing aerosol particles. However, observations of particle formation in clouds are scarce. Here we show measurements indicative of in-situ new particle formation occurring in cirrus clouds. Measurements were made at altitudes from 7 to 16 km over Florida with instruments on the WB-57F aircraft during Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiments (CRYSTAL-FACE) in July 2002. Size-resolved ice crystal particle concentrations and water vapor concentrations were measured to help identify the presence of cirrus clouds. Surprisingly high concentrations of ultrafine particles, diameters (D$_{p}$) from 4 to 9 nm (N$_{4-9}$), were measured in interstitial cirrus cloud aerosol. About 72 % of the in-cloud samples showed new particle formation events with the average N$_{4-9}$ of 3.0x10$^{3}$ cm$^{-3}$, whereas $\sim$56 % of the out-of-cloud samples had events with the lower N$_{4-9}$ of $\sim$1.3x10$^{3}$ cm$^{-3}$. Both size distributions of the in- and out-of- cloud samples with new particle formation events showed a high peak at D$_{p}$ $<$10 nm and another peak at D$_{p}$ $\sim$20 nm. The magnitude and frequency of new particle formation events seen in cirrus clouds were also higher than those previously observed in the tropical/subtropical upper troposphere in the absence of clouds. These results suggest that cirrus clouds may provide favorable conditions for particle formation, such as low temperatures, high relative humidity, high OH production (due to high water vapor), cloud electricity and atmospheric convection; but at present we are unable to identify particle nucleation mechanisms in clouds, a condition where high concentrations of surface area of ice crystal particles exist.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0365 Troposphere--composition and chemistry
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting