HR: 0800h
AN: B51A-0177    [Abstracts]
TI: Nitric Acid Phase Partitioning and Cycling in the New England Coastal Atmosphere
AU: * Fischer, E
EM: efischer@mountwashington.org
AF: Mount Washington Observatory, Research Department, North Conway, NH 03860 United States
AU: Keene, W
EM: wck@virginia.edu
AF: University of Virginia, Department of Environmental Sciences , Charlottesville, VA 22904 United States
AU: Maben, J
EM: jrm@virginia.edu
AF: University of Virginia, Department of Environmental Sciences , Charlottesville, VA 22904 United States
AU: Pszenny, A
EM: apszenny@mountwashington.org
AF: Mount Washington Observatory, Research Department, North Conway, NH 03860 United States
AU: Pszenny, A
EM: apszenny@mountwashington.org
AF: University of New Hampshire, Institute for the Study of Earth, Oceans, and Space , Durham, NH 03824 United States
AU: Smith, A
EM: ams6t@virginia.edu
AF: University of Virginia, Department of Environmental Sciences , Charlottesville, VA 22904 United States
AU: Talbot, R
EM: robert.talbot@unh.edu
AF: University of New Hampshire, Institute for the Study of Earth, Oceans, and Space , Durham, NH 03824 United States
AB: During summer 2004, soluble gases were continuously sampled over 2-hour intervals and size-resolved aerosols were sampled over discrete daytime (~ 15 hr) or nighttime (~ 9 hr) intervals at Appledore Island, ME as part of the International Consortium for Atmospheric Research on Transport and Transformations (ICARTT) field program. Particulate NO₃^- and gaseous HNO₃ concentrations were examined as a function of transport sector and dry deposition fluxes were estimated. HNO₃ concentrations varied widely on the time scale of hours; however, all sampling days were characterized by a distinct minimum in the early morning. The daily peak normally occurred in the early afternoon, and was followed by a secondary peak at about 2200. The maximum and median concentrations of HNO₃, were 337 and 22.5 nmol m^-3 respectively. Aerosol NO₃^- exhibited a bimodal size distribution with a primary peak associated with sea-salt Na⁺ at ~4 μm and a secondary sub-μm peak. The median NO₃^- concentrations of sub and super-μm aerosol fractions were 3.3 and 7.7 nmol m^-3 respectively. HNO₃ concentrations (median value = 57 nmol m^-3) were measured during westerly flow regimes, while super-μm aerosol peaked during southwesterly flow regimes. Although median total nitrate (HNO₃ + NO₃^-)concentrations were higher under westerly flow, higher median dry deposition rates for total nitrate were calculated for southwesterly flow. Both westerly and southwesterly transport regimes carried polluted continental air to the site, but sea-salt concentrations were a factor of 3 higher during southwesterly flow which shifted the phase partitioning toward particulate NO₃^-. Consequently, under westerly flow, the calculated HNO₃ deposition flux was ~3 times greater than the associated aerosol NO₃^- flux, while for southwesterly flow, the fluxes from the two phases were comparable. The median dry deposition fluxes for aerosol NO₃^- and volatile HNO₃ were 5.6 and 8.2 μmol m^-2 d^-1. Large particles dominated the aerosol dry deposition, because of both higher concentrations and deposition velocities. This is consistent with previous work suggesting that the mixing of polluted continental and marine air may enhance dry deposition of total nitrate to coastal ecosystems. Displacement of HCl from sea-salt aerosol via incorporation of HNO₃ helped to sustain high mixing ratios of HCl (up to 255 nmol m^-3) and significant production of atomic Cl via HCl + OH during the daytime, thereby altering the oxidant regime relative to the upwind continent.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
DE: 0368 Troposphere: constituent transport and chemistry
DE: 0469 Nitrogen cycling
SC: Biogeosciences [B]
MN: Fall Meeting 2005