HR: 0800h
AN: B51A-0180    [Abstracts]
TI: Ammonia Sources, Transport, Phase Partitioning, and Deposition in Coastal New England During Summer
AU: * Smith, A M
EM: ams6t@virginia.edu
AF: Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904 United States
AU: Keene, W C
EM: wck@virginia.edu
AF: Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904 United States
AU: Maben, J R
EM: jrm@virginia.edu
AF: Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904 United States
AU: Pszenny, A A
EM: alex.pszenny@unh.edu
AF: Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, NH 03824 United States
AU: Pszenny, A A
EM: alex.pszenny@unh.edu
AF: Mount Washington Observatory, P.O. Box 2310, North Conway, NH 03860 United States
AU: Fischer, E
EM: efischer@mountwashington.org
AF: Mount Washington Observatory, P.O. Box 2310, North Conway, NH 03860 United States
AB: The atmospheric cycling of NH₃ is ecologically important and influenced by both natural and anthropogenic processes. As part of the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) campaign during summer 2004, NH₃, size-resolved particulate NH₄⁺, and associated chemical constituents of near-surface air were measured continuously on Appledore Island, off the southern coast of Maine. Source regions for sampled air parcels were characterized using HYSPLIT back trajectories and FLEXPART retroplumes. NH₃ mixing ratios ranged from <13 to 2728 pmol mol^-1 and exhibited a marked diel cycle with maxima in late afternoon and minima at night. Particulate NH₄⁺ ranged from 229 to 4233 pmol mol^-1. The absolute amount of total NH₃ (NH₃ + particulate NH₄⁺) and its pH-dependent phase partition varied systematically as a function of source region. Under cleaner flow regimes from the NW, N, and E, total NH₃ concentrations were relatively lower (median = 1150 pmol mol^-1) and partitioned roughly equally between phases; under the more polluted W and SW flow regimes, total NH₃ concentrations were relatively higher (median = 1700 pmol mol^-1) and dominated by particulate NH₄⁺. Because most particulate NH₄⁺ was associated with the highly acidic sub-æm size fractions (pH ranging from -0.68 to 3.67) with low deposition velocities (median flux = 1.5 æmol m^-2 day^-1), dry-deposition fluxes were dominated by the gas phase (median = 6.2 æmol m^-2 day^-1). Consequently, controls on phase partitioning, particularly concentrations of pollutant-derived S aerosol, strongly influenced the atmospheric lifetime of total NH₃. Because of differences in phase partitioning, dry-deposition fluxes at relatively higher concentrations of total NH₃ associated with polluted flow regimes (median = 6.7 æmol m^-2 day^-1) were less than those for cleaner regimes (median = 10.5 æmol m^-2 day^-1). The presence of sea salt did not alter the phase partitioning of NH₃ significantly and, thus, the mixing of polluted continental with marine air along the coast had minimal direct influence on the chemical processing and atmospheric lifetime of total NH₃.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
SC: Biogeosciences [B]
MN: Fall Meeting 2005