Results from the DC-8 Inlet Characterization Experiment (DICE): Airborne Versus Surface Sampling of Mineral Dust and Sea Salt Aerosols

During May and June of 2003 NASA conducted the DC-8 Inlet Characterization Experiment (DICE). The study was undertaken to quantify the performance of three passive, solid diffuser inlets used aboard the DC-8 aircraft to sample optically effective aerosol sizes. Aerosol optical properties measured behind the University of Hawai\u27i (UH) and the University of New Hampshire (UNH) inlets were within 10% of the ground based measurements whereas the NASA Langley (LaRC) inlet reduced scattering values for supermicrometer dust by approximately 50%. Based on the DICE results the aerodynamic 50% passing efficiency of the inlets and transport plumbing is determined to be above 5.0 and 4.1 μm for the UH and UNH inlets and 3.6 μm for the LaRC inlet. These aerodynamic sizes correspond to geometric particle diameters of 3.1, 2.5, and 2.0 μm ignoring shape factor and assuming particle densities of 2.6 g cm−3. Sea salt aerosols sampled at high relative humidity revealed that the UH and the UNH inlets performed nearly identically in the marine environment. Aerosol optical properties measured behind the UH inlet were within 30% of measurements made at the NOAA/ESRL Trinidad Head Observatory and in some cases were better than 10%. We conclude that quantitative measurements of optical properties and processes linked to aerosol surface chemistry can be effectively studied aboard the NASA DC-8 using the UH and UNH inlets because aerosol particles less than 4 μm in aerodynamic diameter typically dominate aerosol optical properties and surface area