Design and Calibration of a Multi-Channel Aerosol Sampler for Tropopause Region Studies from the CARIBIC Platform

An aircraft-based, multi-channel aerosol sampler for studies of the upper troposphere and lowermost stratosphere from the CARIBIC (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container) platform was designed and calibrated. The sampler operates with an impaction technique at a flow rate of 10.4 lpm and consists of sixteen sampling channels. Samples are collected in a time sequence. Each channel contains two sample types that are used for quantitative measurement of concentrations, using particle-induced X-ray emission (PIXE), and single particle analysis with electron microscopy. The minimum detection limits for PIXE analysis after 1.5 h sampling are, for example, 2.0, 0.14, and 0.02 ng/m³ STP (standard temperature and pressure) for sulfur, potassium, and nickel. Calibration included penetration studies of a cyclone arrangement used to define the upper size limit in the sampling to 2.0 μ m diameter and the collection efficiency of the impactor. Both components of the sampling system showed penetration and collection efficiency close to 100%, respectively, in the particle size range of interest. The impactor cut-off was found to be dependent on the ratio of the impactor upstream-to-downstream pressure for ratios well below the critical pressure drop (i.e., the pressure where the jet reaches sonic velocity) being 0.15 μ m and 0.08 μ m for ratios 0.41 and 0.2.

The work was supported financially by the European Union, the Swedish Research Council and the Crafoord Foundation (research grants EKV2-CT-2001-00101, 621-2002-5331 and 20020885).

Notes

^a The detection limits are given at the 99% probability level.

^b The detection limits are given at standard temperature and pressure (STP).