FAST OXIDATION REACTION OF NITRITE BY DISSOLVED-OXYGEN IN THE FREEZING PROCESS IN THE TROPOSPHERIC AQUEOUS-PHASE

Citation
N. Takenaka et al., FAST OXIDATION REACTION OF NITRITE BY DISSOLVED-OXYGEN IN THE FREEZING PROCESS IN THE TROPOSPHERIC AQUEOUS-PHASE, Journal of atmospheric chemistry, 29(2), 1998, pp. 135-150
Citations number
25
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Metereology & Atmospheric Sciences","Environmental Sciences
ISSN journal
0167-7764
Volume
29
Issue
2
Year of publication
1998
Pages
135 - 150
Database
ISI
SICI code
0167-7764(1998)29:2<135:FORONB>2.0.ZU;2-K
Abstract
Nitrite oxidation in the tropospheric aqueous phase by freezing was ev aluated by freezing a field sample. Nitrite oxidation by dissolved oxy gen in the freezing process is much faster than by other oxidation pro cesses, such as reactions with ozone, hydrogen peroxide or dissolved o xygen in an aqueous solution at pHs 3 to -6. At pH 4.5 and 25 degrees C, the Lifetime of nitrite in the aqueous phase is ca. 1 hr in oxidati on by ozone (6 x 10(10) mol dm(-3)), ca. 10 hr in oxidation by H2O2 (2 x 10(-4) mol dm(-3)), and 7.5 hr (Fischer and Warneck, 1996) in photo dissociation at midday in summer. Under the same conditions at a tempe rature below 0 degrees C, the lifetime of nitrite in the freezing proc ess is estimated as ca. 2 sec when the droplets are frozen within a se cond. The reaction by freezing is affected by the presence of salts, s uch as NaCl or KCI, or orgnaic compounds, such as methanol or acetone. The results of freezing a field rain or fog sample showed that nitrit e oxidation proceeds below pH 6, and the conversion ratio of nitrate f rom nitrite increases with decreasing pH. The oxidation of nitrite by freezing was also observed in freezing fog particles generated by an u ltrasonic humidifier. The ratios of the concentrations of ions in the winter sample to those in the summer sample (or those in the fog sampl e) were almost the same values. However, the concentration of nitrite in the winter sample was lower than that estimated by the ratios of ot her ions. From the present study, it seems that the freezing process p lays an important role in the nitrite sink process in the tropospheric aqueous phase.