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Published August 1994 | metadata_only
Journal Article

Iron photochemistry of aqueous suspensions of ambient aerosol with added organic acids


Experiments to simulate cloudwater conditions were carried out by using ambient aerosol samples suspended in an aqueous solution. Electron donors known to exist in atmospheric cloudwater (oxalate, formate, or acetate) were then added to the simulated cloudwater, and the solution irradiated with ultraviolet light while important species were measured (i.e., H_2O_2, Fe_(total), Fe(II)_(aq), and pH). A total of four different ambient aerosol samples were used in the simulated cloudwater experiments; they were collected from (1) Whiteface Mountain, NY, (2) Pasadena, CA, and (1) Sequoia National Park, CA. Hydrogen peroxide (H_2O_2) photoproduction was observed in the simulated cloudwater experiments with added oxalate. Fe(II)_(aq) photoproduction was observed in the simulated cloudwater experiments with and without added acetate or added formate using ambient aerosol collected simultaneously with the ambient aerosol used in the added oxalate experiments. The production of Fe(II)_(aq) showed that Fe from the ambient aerosol was available for photochemical redox reactions. In all cases, the production rates for Fe(II)_(aq) and H_2O_2 in the light were greater than production rates in nonirradiated control experiments. The simulated cloudwater experiments (with four different aerosol samples) showed similar behavior to previous experiments carried out with synthetic Fe-oxyhydroxy polymorphs in the presence of oxalate, formate, or acetate. The Fe present in the ambient aerosol appears to be a critical component for the production of H_2O_2 in the simulated cloudwater experiments.

Additional Information

© 1994 Elsevier Science Ltd. Received 15 June 1993, Accepted in revised form 8 April 1994. We thank the staff of ASRC at Whiteface Mountain, especially Anne Foster and Richard MacDonald, and also the staff at Sequoia National Park, especially Diane Ewell and Annie Esperanza, for their help. We also thank Professor Andy Friedland at Dartmouth College. We also thank Professor J. Morgan for helpful discussions, and Mike Wong for his help in the laboratory. We also thank the reviewers for their contributions to the paper. Support for this research has been provided by a grant from the National Science Foundation, Division of Atmospheric Sciences, Atmospheric Chemistry Section (ATM 9015775; ATM-9303024). This research was also sponsored by the US Department of Energy, Office of Energy Research, Environmental Sciences Division, Office of Health and Environmental Research, under appointment to the Graduate Fellowships for Global Change administered by Oak Ridge Institute for Science and Education.

Additional details

August 20, 2023
August 20, 2023