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) at NASA Dryden Flight Research Center at Edwards Air Force Base in the Mojave Desert of California. The study was undertaken in order to quantify the performance characteristics of three passive, solid diffuser type inlets used aboard the DC-8 aircraft to sample optically relevant aerosols. Mineral dust aerosol optical properties measured behind the University of Hawai`i and the University of New Hampshire inlets were within 10% of the ground based measurements whereas the NASA Langley inlet underestimated values for coarse dust aerosol by approximately 50%. Based on these results the 50% passing efficiency of the combined inlets and plumbing to instruments is determined to be above 4.2 and 4.0 μm for the UH and UNH inlets and about 3.4 μm for the LaRC inlet. The latter inlet has been redesigned based upon these comparisons. Sea salt aerosols sampled at high relative humidity (85-95%) also 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/CMDL Trinidad Head Observatory and in some cases were better than 10%. A quantitative determination of the 50% passing efficiency of marine aerosols was not possible as no size information was available at THD. However, at aerosol concentrations comparable to the dust cases ambient sea salt diameters (i.e. equivalent particle wet diameter at the inlet tip) of 4-6 μm were recorded behind the UH and UNH inlets. At higher concentrations, ambient aerodynamic diameters as large as 6-8 μm were recorded by the aerodynamic particle sizers (APSs) behind the UH and UNH inlets. Hence, the passive UH and UNH solid diffuser inlets and associated instrument plumbing evaluated for use aboard the NASA DC-8 during INTEX-NA are adequate for effective representation of typical aerosol optical properties and surface area.

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