HR: 16:00h
AN: A54B-03    [Abstracts]
TI: Optical Properties of Saharan Dust Over the North Atlantic Ocean
AU: * Savoie, D L
EM: dsavoie@rsmas.miami.edu
AF: Marine and Atmospheric Chemistry University of Miami, 4600 Rickenbacker Cswy., Miami, FL 33149 United States
AB: During several intensive field experiments over the tropical North Atlantic, we used a variety of instruments to make extensive measurements of the chemical, physical and optical properties of aerosols in the marine boundary layer at Barbados and Puerto Rico and in the free troposphere at Iza¤a, Tenerife, Canary Islands. The ultimate objective of this work is to determine the mean physical and optical properties of aerosols from specific sources and to assess the variations of these properties as a function of meteorological parameters. Major aerosol sources for this region include Saharan dust, sea-salt, and pollution from Europe and North Africa. This information is critical to properly estimating the affect of aerosols on the propogation of radiation through the atmosphere. Cl-, NO3-, SO4=, Na+, NH4+, and mineral dust are based on 12 or 24-hour high volume bulk aerosol samples. Spectrally-resolved (300-1100 nm at 10 nm intervals) light absorption was measured on portions of the bulk filter using a diffuse reflectance technique. Aerosol light scatter and backscatter were measured at 450, 550, 700 nm wavelengths using a TSI 3563 Integrating Nephelometer; the high frequency data were subsequently averaged over the time periods of the bulk aerosol collections. At Iza¤a, the mass scattering efficiency of Saharan dust increases from 0.43 m2/g at 450 nm to 0.50 at 550 nm to 0.54 at 700 nm. Over the western Atlantic, the mass scattering efficiencies are about 20% higher (about 0.60 m2/g at 550 nm) as a consequence of the loss of the largest dust particles (greater than about 6 um diameter) which have a substantial affect on the mass but make only a minor contribution to the total light scatter. The mass absorption efficiency of Saharan dust is virtually constant across the region but decreases from 0.20 m2/g at 450 nm to 0.09 at 550 to 0.025 at 700. Because absorption follows the mass-partile size distribution, losses of the large particles affects mass and absorption similarly and these affects cancel in the absorption/mass ratio. Because total pollutant particle mass was not measured, total scattering by dry total pollutant particles is presented per gram of sulfate. At Iza¤a during summer 1997, total pollutant scattering decreased from 10.7 m2/g-sulfate at 450 nm to 4.4 at 700 nm, comparable results were obtained during summer 1995. The projects under which these data were collected were funded by NSF-Atmospheric Chemistry, the Navy (ONR), and NASA (TOMS).
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0365 Troposphere--composition and chemistry
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2005 Joint Assembly