HR: 0800h
AN: A31C-0062    [Abstracts]
TI: Overview of the Light Aircraft Aerosol Research Inlet (LAARI)
AU: * Bueno, P A
EM: pedro@umd.edu
AF: Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742 United States
AU: Taubman, B F
EM: btaubman@met.psu.edu
AF: Department of Meteorology, Penn State University, University Park, PA 16802 United States
AU: Marufu, L T
EM: marufu@atmos.umd.edu
AF: Department of Meteorology, University of Maryland, College Park, MD 20742 United States
AB: Aircraft provide a mobile platform for measuring vertical profile aerosol properties. The efficacy of these measurements, however, is constrained by the aerosol inlet sampling efficiency. Larger particles are often lost to turbulent deposition and impaction inside the inlet and sampling lines, respectively. This precludes the measurement of coarse mode particles, important to visibility and radiative transfer studies. Turbulent deposition of large particles occurs when the sample air stream slows down within the inlet from the aircraft velocity to the recommended sampling velocities of the aerosol instruments (\sim10 m s$^{-1}$). Low-turbulence inlets that reduce turbulent deposition through the use of a porous diffuser cones are necessary for large aircraft with air speeds of 80 to 200 m s$^{-1}$, but these are not feasible for light aircraft because of space and power requirements and may not even be necessary given the low air speeds of small aircraft. We have designed an aerosol inlet for a light aircraft platform with an average air speed of 60 m s$^{-1}$ and a sample flow rate of 28.5 L min$^{-1}$. The hemi-elliptical shaped, stainless steel inlet is 12.7 cm long. The front orifice has a 0.3175 cm diameter and the internal diameter expands to 0.9525 cm over a length of 9.2075 cm at an included angle of 4.3\deg. The linear velocity of the sample stream as it exits the inlet is 6.7 m s$^{-1}$. The calculated Reynolds number (Re) at the opening is 11,430 and decreases to 3,811 at the inlet terminus, with a pressure drop across the inlet opening of only 42 mb at an average flight temperature and pressure. Sampling line impaction is reduced by decreasing the number of bends upstream of the instruments. We have accomplished this by designing a parallel sampling manifold that splits the sample stream into four separate streams, three of which are split from the primary sample stream at an angle of 15\deg. Theoretical investigations of sample flow and particle losses are underway with Computational Fluid Dynamics (CFD) software from FlowLab. Wind tunnel analyses using a Vibrating Orifice Aerosol Generator (VOAG) with optical particle counters upstream and downstream of the inlet and sampling lines will validate the theoretical calculations and provide empirical sampling efficiency values. This new inlet design will facilitate the more efficient collection of ambient particles, especially those in the coarse mode, from light aircraft. Because light aircraft are less expensive to operate than large aircraft and can make measurements in the lower atmosphere on a more routine basis, the Light Aircraft Aerosol Research Inlet (LAARI) will herald a new era of measurement capabilities in satellite validation work, column closure tests, and climate change studies.
DE: 3394 Instruments and techniques
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0345 Pollution--urban and regional (0305)
DE: 0394 Instruments and techniques
DE: 0399 General or miscellaneous
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting