HR: 14:25h
AN: A13G-04    [Abstracts]
TI: Black carbon in cloud residual nuclei during PACDEX: Combining the single particle soot photometer and the counterflow virtual impactor
AU: * Kok, G
EM: glkok@dropletmeasurement.com
AF: Droplet Measurement Technologies, 5710 Flatiron Parkway, Suite B, Boulder, CO 80301, United States
AU: Subramanian, R
EM: random@dropletmeasurement.com
AF: Droplet Measurement Technologies, 5710 Flatiron Parkway, Suite B, Boulder, CO 80301, United States
AU: Twohy, C
EM: twohy@coas.oregonstate.edu
AF: Oregon State University, College of Oceanography and Atmospheric Sciences, Corvallis, OR 97331, United States
AU: Baumgardner, D
EM: darrel@servidor.unam.mx
AF: Universidad Nacional Autonoma de Mexico, Centro de Ciencias de la Atmosfera, Mexico City, 04510, Mexico
AB: The single particle soot photometer (SP2) measures black carbon (BC) using laser incandescence. In the PACific Dust EXperiment (PACDEX), the SP2 was operated downstream of a counterflow virtual impactor (CVI) during flight portions when the aircraft was passing through a cloud. The CVI collects cloud droplets and ice crystals larger than 5 μm and evaporates the water content, so that residual nuclei are sampled. The CVI also concentrates the incoming air-stream by as much as a factor of 30 or more. The combination of the SP2 with the CVI enables BC measurements below a few ng/m³. Preliminary results indicate that compared to aerosol in the surrounding air mass, black carbon concentrations (per unit volume air) were generally lower in cloud, but a greater fraction of cloud residual particles contain BC. Cloud residual nuclei also seem to contain more BC mass/particle than the ambient aerosol. The May 5 flight made a number of passes through a Pacific frontal system. During one such pass at 8.3 km ASL, BC in residual nuclei sampled through the CVI was on average 0.4 ng/m³ with a mean incandescent particle concentration of 0.1 particles/cm³, compared to over 7 ng/m³ and 2.5 particles/cm³ in ambient aerosol behind the front. For total concentrations over 0.2 particles/cm³ as detected by the SP2, the fraction of cloud nuclei that incandesced or contained BC was often greater than the incandescing fraction of the ambient aerosol at the same altitude, with up to 40% of cloud nuclei incandescing compared to ~10-25% for ambient aerosol. BC mass distributions peaked around 5 fg-BC/particle in ambient air. Inside the front, BC mass distributions in cloud nuclei were broader with peaks between 10-23 fg-BC/particle. Possible explanations for these results are that either BC-containing particles are scavenged by clouds, or these particles are good cloud nuclei, with larger aerosol containing more BC mass/particle preferentially forming cloud droplets and ice crystals.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting