Journal of Atmospheric Chemistry

, Volume 58, Issue 2, pp 89–109 | Cite as

Photochemistry of Cu complexed with chromophoric dissolved organic matter: implications for Cu speciation in rainwater

  • Melanie Louise Inez Witt
  • Stephen Skrabal
  • Robert Kieber
  • Joan Willey


Significant quenching of fluorescence by Cu in rainwater samples from southeastern North Carolina demonstrates that chromophoric dissolved organic matter (CDOM) is an effective ligand for Cu in rainwater. A strong inverse correlation between the decrease in fluorescence upon Cu addition and CDOM abundance suggests the presence of excess binding sites for Cu in high CDOM samples. Electroanalytical studies indicate that CDOM extracted from C18 cartridges formed Cu complexes with concentrations and conditional stability constants similar to ligands found in ambient rainwater. When authentic rainwater samples were photolyzed with simulated sunlight both photoproduction and photodestruction of ligands were observed, suggesting the photochemical response of Cu-complexing ligands in rainwater is the result of two competing reactions. The rate of CDOM photobleaching was directly related to changes in strong ligands (KCuL ∼ 1015) whereas weaker ligands (KCuL < 1013) were not correlated, suggesting the photolabile CDOM resides in the strong ligand class. A photolysis study comparing filtered and unfiltered rainwater samples indicated that Cu-complexing ligands adsorbed onto or otherwise associated with particles are photodegraded much more rapidly than dissolved ligands. Photolysis with UV radiation appears to be most effective at engendering changes in Cu ligands, however a significant photochemical response was also observed when samples were exposed to photosynthetically active radiation with wavelengths greater than 400 nm. Results from this study demonstrate that complexation of Cu by CDOM has important ramifications for controlling both the speciation of the metal and the reactivity of CDOM in rainwater.


Atmosphere Chromophoric dissolved organic matter Copper Metals Photochemistry Precipitation Speciation 



This research was supported by the National Science Foundation through grants ATM-0342420 and OCE-0326685. The Marine and Atmospheric Chemistry Research Laboratory group at UNCW assisted with sampling and analyses. The authors thank the maintenance staff at UNCW for their assistance with the running of the rain collection site. We are grateful to 2 anonymous reviewers for their thoughtful comments.


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Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • Melanie Louise Inez Witt
    • 1
    • 2
  • Stephen Skrabal
    • 1
  • Robert Kieber
    • 1
  • Joan Willey
    • 1
  1. 1.Department of Chemistry and BiochemistryUniversity of North Carolina WilmingtonWilmingtonUSA
  2. 2.Department of Earth SciencesUniversity of OxfordOxfordUK

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