title: Photoformation rate, steady-state concentration and lifetime of nitric oxide radical (NO·) in a eutrophic river in Higashi-Hiroshima, Japan.
abstract: Monthly measurements (January-December 2013) of the photoformation rate, steady-state concentration and lifetime of nitric oxide radical (NO·) in the Kurose River in Higashi-Hiroshima City, Japan, were obtained. Each month, river water samples were collected at six different stations (upstream to downstream). NO· was quantified using 4, 5-diaminofluorescein-2 (DAF-2) as a probe and triazolofluorescein (DAF-2T) as a standard. Results show that NO· photoformation rate ranged from 0.01 to 35.4 (×10(-10) M s(-1)). The radical steady-state concentration in the river ranged from 0.02 to 68.5 (×10(-11) M). There was a strong correlation (r(2)=0.95) between NO· photoformation rate and the nitrite concentration in the river suggesting that this anion is a major NO· precursor. On average, 98% of the photoformed NO· came from river nitrite, and this was calculated using the photoformation rate constant {5.7×10(-5) M(NO·)s(-1) M(NO2(-))(-1)} of NO· from the anion concentration found in the study. The NO· lifetime ranged from 0.05 to 1.3 s in the river and remained fairly stable in the upstream and downstream samples. The ·OH radical, which was quantified during the study, had a photoformation rate of 0.01-13.4 (×10(-10) M s(-1)) and a steady-state concentration of 0.04-119 (×10(-16) M) with a lifetime that ranged from 0.3 to 22.5 (×10(-6) s). ·OH only accounted for ⩽0.0011% of the total NO· scavenged, showing that it was not a major sink for river NO·.
authors.affiliation: Department of Environmental Dynamics and Management, Graduate School of Biosphere Science, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan. Electronic address: chemistbanjo@yahoo.com.
authors.forename: Adebanjo Jacob
authors.initials: AJ
authors.lastname: Anifowose
authors.affiliation: Department of Environmental Dynamics and Management, Graduate School of Biosphere Science, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan. Electronic address: takedaq@hiroshima-u.ac.jp.
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Takeda
authors.affiliation: Department of Environmental Dynamics and Management, Graduate School of Biosphere Science, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan. Electronic address: hsakuga@hiroshima-u.ac.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sakugawa
mesh_terms: D007564:Japan; D009569:Nitric Oxide / Q000032:analysis* / Q000737:chemistry*; D009573:Nitrites / Q000737:chemistry* / Q000528:radiation effects*; D010782:Photolysis; D045483:Rivers / Q000737:chemistry; D013472:Sunlight
chemical_list: D009573:Nitrites; D009569:Nitric Oxide
keywords: Nitric oxide; Nitrite; Photoformation rate; Radical; River water; Steady-state concentration