ABSTRACT
This chapter examines the role of transition metals occurring in atmospheric water. It shows that reported concentrations of iron in such atmospheric waters are of comparable magnitudes as those measured for oxalic acid. In the low pH range of atmospheric waters, dissolved oxygen will reoxidize Fe(II) only through very slow reactions. Instead, reoxidations will occur via reactions of atmospheric photooxidants. An Fe(III)-Fe(II) photochemical-chemical cycle occurs in atmospheric waters. Also, quantum efficiencies for the photolysis of the iron oxalate species are much higher than those reported for the Fe(III)-hydroxo complexes. The primary ligand-to-metal charge-transfer process occurring in the photoexcited state is able to transfer an electron to oxygen. This leads to the formation of Oxalic acid is thereby oxidized to CO2 Fe(II) is released. The situation is rather different from that occurring at high concentrations of iron oxalate typically applied for actinometry; in such solutions, the oxalate radical is oxidized by Fe(III) oxalate.
