CIFEX Experiment # 8

April 10, 2004.

Flight Scientist: Guillaume Mauger

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Flight #11 : Take off about 10 am. Lasted about 3 hours

Flight # 12 : Take off about 4.30 pm. Lasted about 3 hours

Objective: To fly level legs in a vertical section, in order to obtain improved aerosol statistics, namely for the aethalometer.

A high to the NE led to persistent clear skies, and we decided to sample a cross section of the atmosphere just off-coast, in order to improve our estimates of single scattering albedo. We flew a North-South section at 125W, chosen to maintain constant aerosol concentrations, as predicted by CFORS. A total of 5 separate altitudes were sampled, with flight legs of 25min. in length: at 15,000, 12,000, 8700, 5400, and 1000ft. An initial profile provided an approximate location of the pollution plumes. At 15,000 ft, free tropospheric aerosol concentrations were observed (CPC ~ 200/cc), with some indication of processing (the size distribution was flat, followed by a broad peak around 70nm). Descending to 12,000 ft, we encountered a plume with a CPC concentration of about 600/cc. Lack of a corresponding change in the PCASP, and SMPS spectra both provided evidence of new particle formation. We settled on a 3 rd leg at 8,700 ft, after unsuccessfully searching for a previously observed aerosol layer (subsequent profiling indicated that it was slightly below us). At 8,700 ft, the aerosol showed a trimodal SMPS distribution, with peaks above, near, and below 100nm. CPC concentrations held near 300/cc. For the 4 th leg, we attempted to fly just beneath the top of the boundary layer, as defined by the region of elevated CPC concentrations. We seem to have been flying within a rather abrupt vertical gradient, leading to spikes in the aerosol concentrations: CPC ~ 1400, and PCASP ~ 150/cc. The final leg, at 1000ft, showed CPC concentrations of ~2000, and PCASP ~ 250/cc. OF NOTE: the relative humidity was at 15% down to our lowest flight, which may have significantly reduced the scattering due to aerosols. Subsequent analysis of lower elevations sampled during take-off and landing revealed a thermodynamic boundary layer that was capped below 600ft altitude.