HR: 13:40h
AN: A33G-01    [Abstracts]
TI: Tropical Marine Clouds: Sinks, Sources and Transformers of CCN
AU: * Clarke, A
EM: tclarke@soest.hawaii.edu
AF: University of Hawaii, Department of Oceanodraphy, 1000 Pope Rd., MSB501, Honolulu, HI 96822, United States
AU: Howell, S
EM: showell@soest.hawaii.edu
AF: University of Hawaii, Department of Oceanodraphy, 1000 Pope Rd., MSB501, Honolulu, HI 96822, United States
AU: Freitag, S
EM: SteffenFreitag@web.de
AF: University of Hawaii, Department of Oceanodraphy, 1000 Pope Rd., MSB501, Honolulu, HI 96822, United States
AU: Blomquist, B
EM: blomquis@hawaii.edu
AF: University of Hawaii, Department of Oceanodraphy, 1000 Pope Rd., MSB501, Honolulu, HI 96822, United States
AU: Blomquist, B
EM: blomquis@hawaii.edu
AF: Drexel University, Department of Chemistry, 3141 Chestnut Street, Philadelphia, PA 19104, United States
AU: Bandy, A
EM: bandyar@drexel.edu
AF: Drexel University, Department of Chemistry, 3141 Chestnut Street, Philadelphia, PA 19104, United States
AU: Mauldin, L
EM: mauldin@ucar.edu
AF: NCAR/ACD, 1850 Table Mesa POB 3000, Boulder, CO 80303-3000, United States
AU: Anderson, R
EM: rca@ucar.edu
AF: NCAR/ACD, 1850 Table Mesa POB 3000, Boulder, CO 80303-3000, United States
AB: During August of 2007 the Pacific Atmospheric Sulfur Experiment (PASE) investigated the sulfur cycle using 13 NCAR C-130 aircraft missions based out of Christmas Is. (2N, 157W). Part of this study examined the origin and evolution of aerosol in the cloudy equatorial marine boundary layer, MBL, and their relation to effective cloud condensation nuclei, CCN. These data confirm that most of these particles originate through nucleation in the free troposphere FT, and are entrained into the MBL where they establish most of the MBL particle number. No homogeneous nucleation of particles was observed in the MBL. A separate mode is generated at the ocean surface as sea-salt with a number peak below about 0.1 μm that also grows heterogeneously. Most particles in the equatorial FT appear to be volatile sulfates generated in cloud outflow. A smaller number fraction with refractory (stable at 300C) cores co-vary with ozone and appear to be related to the long range transport of particles in the FT. All FT particles were measured as a monomodal number distribution that subside and then evolve into bimodal number distributions in response to cloud processing in the buffer (cloud) layer and subsequently in the MBL. Here particles increased their mass through heterogeneous gas to particle conversion primarily linked to the sulfur cycle. Measurements confirmed that non-precipitating clouds in the MBL act as a chemical factory for gas-to-particle conversion. This process results in the development in a Hoppel minima near 0.08 um and preferentially adds mass to the larger sizes activated as CCN. When such clouds grow into precipitating Cu with tops above about 4km they act to scavenge the larger aerosol through precipitation. Active precipitation in these regions was also associated with a reduction in CCN concentrations and aerosol mass. However, the outflow and anvil regions of these clouds revealed that CCN sizes were scavenged via precipitation but this air included enhanced SO2 and sulfuric acid pumped aloft where they coincided with regions of new particle formation. Hence, clouds in the tropical MBL act to convert most of the sulfur mass originating from DMS onto existing aerosol at CCN sizes and also serve to remove this mass when they precipitate. Depleted particle number can also be replenished aloft by precipitating clouds dependent upon the details of the scavenging, gas phase sources, photochemisty and thermodynamic considerations near the outflow regions.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0319 Cloud optics
DE: 0320 Cloud physics and chemistry
DE: 0321 Cloud/radiation interaction
DE: 4801 Aerosols (0305, 4906)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting