title: Wavelength dependence of Fe(ll) photoformation in the water-soluble fraction of aerosols collected in Okinawa, Japan.
abstract: We studied photoformation of Fe(II) in the water-soluble fractions (WSFs) of bulk aerosol particles collected in Okinawa, Japan, using radiation at wavelengths of 313, 334, 366, and 405 nm. Fe(II) photoformation quickly reached a steady state within 5 min of irradiation at all wavelengths. The steady-state Fe(II) concentrations were 85+/-13% (n = 39) of the total dissolved Fe (TDFe) concentrations in the WSF solutions. Apparent quantum yields of Fe(II) photoformation were determined based on total absorbance of the WSF solutions, and the means (+/-1 S.D.) were 0.019 (+/-0.034), 0.021 (+/-0.031), 0.014 (+/-0.023), and 0.010 (+/-0.025) at 313, 334, 366, and 405 nm, respectively. Comparison of the observed rates of Fe(II) photoformation for the WSF solutions and the calculated rates from the known Fe(II)-forming compounds suggested that Fe(oxalate)2- could account for the observed Fe(II) photoformation rates if the Fe(oxalate)2- concentration is sufficiently high (>20% of [Fe(III)]o). Furthermore, our study showed that the calculated wavelength dependence of Fe(ll) photoformation from Fe(oxalate)2- was consistent with that of Fe(II) photoformation observed in the WSF solutions. The results obtained here have implications to daytime Fe(III)/ Fe(II) cycles in the atmospheric water droplet.
authors.affiliation: Graduate School of Engineering and Science, University of the Ryukyus, 1 Senbaru Nishihara-cho, Okinawa 903-0213, Japan.
authors.forename: Kouichirou
authors.initials: K
authors.lastname: Okada
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Kuroki
authors.forename: Yoshihide
authors.initials: Y
authors.lastname: Nakama
authors.forename: Takemitsu
authors.initials: T
authors.lastname: Arakaki
authors.forename: Akira
authors.initials: A
authors.lastname: Tanahara
mesh_terms: D000336:Aerosols; D002851:Chromatography, High Pressure Liquid; D005296:Ferrous Compounds / Q000737:chemistry*; D007564:Japan; D011789:Quantum Theory; D012995:Solubility; D014867:Water
chemical_list: D000336:Aerosols; D005296:Ferrous Compounds; D014867:Water