HR: 0800h
AN: A41C-07    [Abstracts]
TI: Photodegradation of Chromophoric Dissolved Organic Matter (CDOM) in Atmospheric Waters and its Influence on the Redox Chemistry of the Troposhere
AU: * Kieber, R J
EM: kieberr@uncw.edu
AF: University of North Carolina Wilmington, Department of Chemistry and Biochemistry, Wilmington, NC 28403, United States
AU: Willey, J D
EM: wileyj@uncw.edu
AF: University of North Carolina Wilmington, Department of Chemistry and Biochemistry, Wilmington, NC 28403, United States
AU: Whitehead, R F
EM: whiteheadrf@uncw.edu
AF: University of North Carolina Wilmington, Center for Marine Science, Wilmington, NC 28403, United States
AU: Avery, G B
EM: averyg@uncw.edu
AF: University of North Carolina Wilmington, Department of Chemistry and Biochemistry, Wilmington, NC 28403, United States
AU: Seaton, P J
EM: seatonp@uncw.edu
AF: University of North Carolina Wilmington, Department of Chemistry and Biochemistry, Wilmington, NC 28403, United States
AB: The abundance and spectral characteristics of chromophoric dissolved organic matter (CDOM) was determined in atmospheric waters in Wilmington, North Carolina USA over an 18 month sampling period. Fluorescence excitation - emission spectra (EEMs) of condensed phase samples showed four major peaks which were indicative of both terrestrial and marine influences. The absorbance spectra of samples generally decreased exponentially with wavelength between 250 and 550 nm with little or no measurable absorbance past 550 nm. Significant photobleaching of both fluorescence and absorbance was observed upon irradiation for 12 hours under simulated sunlight while dark controls remained unchanged, suggesting CDOM is very photolabile. Quantum yield studies revealed that the efficiency of photobleaching decreases rapidly with increasing wavelength for all regions. The spectral characteristics of CDOM and its photodegradation rate were also directly influenced by the presence of ambient levels and speciation of iron and copper in rainwater. These results suggest that highly absorbing and fluorescing CDOM has a direct impact on the redox chemistry of the troposphere and may play a previously unrecognized role in the wavelength dependent spectral attenuation of solar radiation by atmospheric waters. Model calculations suggest there will be measurable changes in stratospheric ozone at temperate latitudes during the next decade. This will significantly impact all atmospheric processes which are photochemically driven including those involving CDOM. Any changes in CDOM photochemistry caused by changing atmospheric conditions will alter the spectral attenuation of solar radiation as well as the free radical and trace metal chemistry of the troposphere. Additionally, if CDOM constituents are surface-active they will have a direct impact on droplet population and consequently cloud albedo by lowering the surface tension of atmospheric waters.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
DE: 1029 Composition of aerosols and dust particles
DE: 3311 Clouds and aerosols
DE: 4801 Aerosols (0305, 4906)
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly