Sampling Characteristics of an Aircraft-Borne Aerosol Inlet System

Abstract

When sampling aerosol particles from aircraft, the inlet system is the most critical item because it can strongly modify the number concentration, size distribution, and chemical composition of the particles. In this investigation, the authors describe a new aircraft-borne aerosol inlet and its sampling characteristics for submicrometer particle measurements in the upper troposphere and lower stratosphere. The new inlet is flown regularly on board a civil aircraft (Boeing 767 300ER) as part of the CARIBIC project. To investigate the sampling characteristics of the new inlet, a wind-tunnel study has been performed. Furthermore, particle transport losses in the sampling line have been calculated. Combining these results, an overall size-resolved inlet system sampling efficiency is given. During transport of the aerosol from the ambient environment to the measurement devices inside the aircraft, the aerosol experiences a strong heating within a few tenths of a second. To estimate the effects of this heating on the size distribution of the sampled particles, model calculations have been performed assuming the sampled particles to consist of sulfuric acid and water. The results show that a significant amount of water evaporates from the sampled particles, whereas sulfuric acid evaporation is so slow that it is negligible for particles larger than 4 nm.