PELTI: Passing Efficiency of the Low-Turbulence Inlet

Summary

In July, 2000 we tested the new porous-diffuser low-turbulence inlet (LTI), developed at the University of Denver, by flying it and three other inlets on NCAR?s C-130 in the Caribbean, using both dust and sea salt as test aerosols. Aerosols were analyzed using bulk chemical analysis of ions on filters, scanning electron microscopy (SEM) of filters, TSI aerodynamic particle sizers (APSs), and FSSP-300 (300) optical particle counters.

We found that the LTI consistently admitted more particles to the airplane than did either the NCAR Community Aerosol Inlet (CAI) or a shrouded solid-diffuser/curved-tube inlet (SD). APS size distributions behind the other inlets began to diverge from LTI values above 1-3 um, with mass concentrations of larger particles lower by as much as a factor of ten behind the CAI and a factor of 2 behind the SD. Modeling of particle trajectories in the LTI with Fluent predicts less than a factor of two enhancement of particles between a few and 7 microns. This was supported by the SEM analyses of particles behind the LTI and TAS.

The experiment concluded that the LTI represents a significant advance in our ability to sample populations of large particles from aircraft. Its efficiency is near enough to unity to enable defendable studies of the distributions and impacts of both mineral dust and sea salt. Corrections will need to be applied for enhancement of particles in the 3-7 um range. We recommend that the ACE-Asia program use LTIs to provide samples to the various aerosol instruments on board the NCAR C-130.