HR: 0800h
AN: A41C-08    [Abstracts]
TI: Physicochemical transition of long-range transport its effect on cloud condensation nuclei over the Eastern Pacific Ocean
AU: * Roberts, G
EM: greg@fiji.ucsd.edu
AF: Scripps Institution of Oceanography, Center for Atmospheric Sciences, La Jolla, CA 92093, United States
AU: Gilardoni, S
EM: sgilardoni@ucsd.edu
AF: Scripps Institution of Oceanography, Center for Atmospheric Sciences, La Jolla, CA 92093, United States
AU: Takahama, S
EM: stakahama@ucsd.edu
AF: Scripps Institution of Oceanography, Center for Atmospheric Sciences, La Jolla, CA 92093, United States
AU: Russell, L
EM: lmrussell@ucsd.edu
AF: Scripps Institution of Oceanography, Center for Atmospheric Sciences, La Jolla, CA 92093, United States
AU: Tomlinson, J
EM: jtomlin@ariel.met.tamu.edu
AF: Texas A&M University, Department of Atmospheric Sciences, College Station, TX 77843, United States
AU: Collins, D
EM: dcollins@tamu.edu
AF: Texas A&M University, Department of Atmospheric Sciences, College Station, TX 77843, United States
AU: Dunlea, E
EM: edward.dunlea@colorado.edu
AF: University of Colorado, Dept. of Chemistry & Biochemistry, Boulder, CO 80309, United States
AU: Jimenez, J
EM: jose.jimenez@colorado.edu
AF: University of Colorado, Dept. of Chemistry & Biochemistry, Boulder, CO 80309, United States
AB: The Intercontinental Chemical Transport Experiment - Phase B (INTEX-B), which occurred in April 2006, focused on the transport and transformation of gases and aerosols on transcontinental and intercontinental scales to assess their impact on air quality and climate. Airborne measurements allow nearly complete characterization of the physicochemical properties of aerosol which allow an independent assessment of their mixing states and ability to act as cloud condensation nuclei (CCN). This chemical information, in conjunction with measurements of aerosol size distribution, investigates the concept of activation indices, which relate the efficiency of an aerosol to serve as CCN based on the relative amount of water-soluble material. During this experiment, we observed variety of aerosol layers during vertical and horizontal profiles, ranging from aged aerosols from major Asian dust storms to ultrafine particles from recent nucleation events. Aerosol layers observed during the flights were found in thin stratified layers ranging from altitudes of 1000 meters to 7000 meters and thicknesses from 100 to 1000 meters. Size resolved chemical measurements indicate cloud processed aerosol in the boundary layer and both aged and ultrafine layers aloft. Aerosols originating undergoing cloud processing activate close to the (NH₄)₂SO₄ limit (activation index near unity); while those with anthropogenic origins show lower activation indices which points to an insoluble or hydrophobic core (i.e., biomass burning or dust) that has been aged by deposition of a water-soluble material. A comparison of the aerosol size distributions to the measured CCN concentration provides insight to the chemical evolution of the aerosols and their potential effect on aerosol/cloud interactions during long-range transport. In some cases, the aerosols have been transported across the Pacific without undergoing cloud processing. Research flight 5 was the first flight during INTEX-B that transected long-range transport of aerosols originating from Asia. Back-trajectories show that airmasses aloft (z = 5000 m) originated from Asia while lower trajectories (z < 3500 m) recirculated in a low pressure region off the Alaskan coast. There had been clouds and precipitation a day or two before sampling, so the CCN below 3500 m were probably removed from wet deposition. Size distributions below 3500 m showed only particles less than 40 nm diameter indicating a recent nucleation event. A vertical profile of the CCN and CN during the flight shows a superposition of seven thin layers on top of a 2km thick layer. The 2km thick layer shows an increase in CCN concentrations (and scattering and larger particles) - this aerosol is presumably aged, long-range transport with Asian origins. As the vertical profile occurred near a frontal system, the source of the sub-layers may be from the Arctic recirculation pool. Further chemical analysis will determine its origins. The profile seems to show that horizontal mixing during long-range transport may be more significant than vertical mixing, which has important implications on the influence of CCN on the aerosol indirect effect. These layers may have a greater impact on the direct effect during transport unless vigorous mixing brings the aerosol into the boundary layer.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0325 Evolution of the atmosphere (1610, 8125)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly