HR: 1340h
AN: B13B-0222    [Abstracts]
TI: Dry Deposition of Fine Aerosol Nitrogen to an Agricultural Field Measured by Eddy-Correlation Mass Spectrometry
AU: * Gonzales, D A
EM: daniel.gonzales@asu.edu
AF: Chemical and Materials Engineering, Arizona State University, PO Box 876006, Tempe, AZ 85287-6006 United States
AU: Allen, J O
EM: joallen@asu.edu
AF: Chemical and Materials Engineering, Arizona State University, PO Box 876006, Tempe, AZ 85287-6006 United States
AU: Allen, J O
EM: joallen@asu.edu
AF: Civil and Environmental Engineering, Arizona State University, PO Box 875306, Tempe, AZ 85287-5306 United States
AU: Smith, K A
EM: kas@mit.edu
AF: Chemical Engineering, Massachusetts Institute of Technology, Room 66-540, Cambridge, MA 02139 United States
AU: Hope, D
EM: di.hope@asu.edu
AF: Center for Environmental Studies, Arizona State University, PO Box 873211, Tempe, AZ 85287-3211 United States
AB: In urban areas high emissions of reactive nitrogen species cause an increase in atmospheric aerosol nitrogen formation and deposition. This nitrogen is eventually removed from the atmosphere by wet or dry deposition, with dry deposition often accounting for more than half of the total deposition of particulate nitrate (Lovett, 1994). Total N deposition is not adequately characterized, in part because dry deposition is difficult to measure or model. For example measured fine particle deposition to a forest canopy differs from predicted values by an order of magnitude (Gallagher et al., 1997). The eddy-correlation technique is a micrometeorological method used to directly measure fluxes from measurements made above the surface (Wesely and Hicks, 2000). Eddy-correlation mass spectrometry (ECMS) has been developed to directly measure aerosol particle deposition velocities from fast response aerosol concentration and wind velocity measurements. Using an Aerodyne Aerosol Mass Spectrometer (AMS) (Jayne et al., 2000), the size and composition of ambient aerosols is measured at a high frequency. The AMS signal is proportional to non-refractory PM$_{1.0}$ mass. Aerosol deposition fluxes for a given averaging period are then calculated directly as the covariance of the vertical wind velocity with the AMS signal ($F = -\overline{w'S'}$). A field study was conducted to measure aerosol nitrogen dry deposition to an agricultural field immediately downwind of the Phoenix metropolitan area using eddy-correlation mass spectrometry. The study was supplemented with aerosol composition measurements including bulk deposition collectors and filter bank samplers. Bulk deposition samples and 24-hour filter samples were analyzed for ammonia and nitrogen. Here we compare the results of the flux estimates from bulk collection with inferential measurements (filter samples and modeled deposition velocities) and direct micrometeorological measurements (ECMS) in order to improve N deposition estimates.
DE: 1615 Biogeochemical processes (4805)
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0315 Biosphere/atmosphere interactions
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting