HR: 1330h
AN: A32A-0117    [PDF]
TI: Eddy Correlation Measurements of the Air/Sea Flux of DMS Using Atmospheric Pressure Chemical Ionization Mass Spectrometry
AU: * Marandino, C A
EM: cmarandi@uci.edu
AF: University of California, Irvine, Department of Earth System Science 1212 Croul Hall, Irvine, CA 92697 United States
AU: DeBruyn, W J
EM: debruyn@chapman.edu
AF: Chapman University, Department of Physical Sciences Chapman University 1 University Dr., Orange, CA 92866 United States
AU: Saltzman, E S
EM: esaltzman@uci.edi
AF: University of California, Irvine, Department of Earth System Science 1212 Croul Hall, Irvine, CA 92697 United States
AB: The physical and chemical processes controlling gas exchange across the air/sea interface are not well understood. Many laboratory and field studies of the physical controls on gas exchange have been performed using indirect mass balance measurement techniques, but there have been few direct gas flux measurements over the ocean. Eddy correlation is a micrometeorological technique, which can measure fluxes directly. The use of this technique for trace gas flux measurements has been limited in part due to the lack of sufficiently sensitive, fast-response gas detectors. Atmospheric pressure chemical ionization mass spectrometry (API/CIMS) is a highly sensitive, fast response detection method. We carried out a field study at the Scripps Institute of Oceanography pier to test the use of API/CIMS for eddy correlation flux measurements of dimethylsulfide (DMS). Cospectra of vertical winds and DMS demonstrate that flux from the sea surface was routinely detected. The API/CIMS detected atmospheric fluctuations less than 0.5 Hz. This frequency cut-off probably reflects attenuation in the inlet tubing rather than in the detector itself. The partial pressure of DMS in surface seawater was also determined using the API/CIMS, after equilibration with N2 in a continuous flow membrane equilibrator. Gas exchange coefficients were computed from the flux and air/sea concentration gradient. Gas transfer coefficients determined in this study ranged from 0.66 cm/hr to 38.43 cm/hr, for mean horizontal wind speeds ranging from 1 to 6 m/s. The gas transfer coefficients are positively correlated with wind speed, but are significantly greater than current estimates of gas transfer coefficients at similar wind speeds over the ocean. These elevated gas transfer coefficients probably reflect enhanced water-side turbulence induced by the interaction of wave motion with the shallow bottom at this site.
DE: 0312 Air/sea constituent fluxes (3339, 4504)
DE: 0330 Geochemical cycles
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting