TY - JOUR
T1 - Autoxidation of N(III), S(IV), and other species in frozen solution - A possible pathway for enhanced chemical transformation in freezing systems
AU - Betterton, Eric A.
AU - Anderson, Darcy J.
N1 - Funding Information:
We gratefully acknowledge the financial support of the National Science Foundation (award ATM9409776). We also thank Brian Barbaris, Sabine Philippin, Keith Nelson, and David Ashby for assistance in the laboratory and Margaret Sanderson Rae and Gina Wasson for editing and final preparation of the manuscript.
PY - 2001
Y1 - 2001
N2 - Freezing dilute aqueous solutions of certain oxidizable species such as nitrite and sulfite can promote the rate of autoxidation, instead of retarding it. Experiments show that nitrite and sulfite undergo rapid oxidation to nitrate and sulfate, respectively, in high yield (>90% under certain conditions) when their dilute (100 μM) aqueous solutions are frozen for 10-60 min. at -10 to -40°C. For example, the pseudo-second-order rate constant for nitrite autoxidation, k′, defined in d[NO3-]/dt = 2k′ [HNO2]2, reaches a maximum value of 117 ± 14 M-1s-1 at -15.5°C. This counterintuitive result is hypothesized to be the result of a freeze-concentration effect that occurs when reactants are concentrated into liquid micropockets ahead of the advancing ice front. Oxidation by hydrogen peroxide is also accelerated upon freezing. Since the yields and rates may be high compared to other competing pathways, this process may be significant where freeze/thaw cycles occur naturally, e.g., in glaciating clouds, snow packs, glaciers, and melt ponds on polar sea ice.
AB - Freezing dilute aqueous solutions of certain oxidizable species such as nitrite and sulfite can promote the rate of autoxidation, instead of retarding it. Experiments show that nitrite and sulfite undergo rapid oxidation to nitrate and sulfate, respectively, in high yield (>90% under certain conditions) when their dilute (100 μM) aqueous solutions are frozen for 10-60 min. at -10 to -40°C. For example, the pseudo-second-order rate constant for nitrite autoxidation, k′, defined in d[NO3-]/dt = 2k′ [HNO2]2, reaches a maximum value of 117 ± 14 M-1s-1 at -15.5°C. This counterintuitive result is hypothesized to be the result of a freeze-concentration effect that occurs when reactants are concentrated into liquid micropockets ahead of the advancing ice front. Oxidation by hydrogen peroxide is also accelerated upon freezing. Since the yields and rates may be high compared to other competing pathways, this process may be significant where freeze/thaw cycles occur naturally, e.g., in glaciating clouds, snow packs, glaciers, and melt ponds on polar sea ice.
KW - Autoxidation
KW - Frozen solution
KW - Ice chemistry
KW - Nitrite
KW - Sulfite
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U2 - 10.1023/A:1011907819486
DO - 10.1023/A:1011907819486
M3 - Article
AN - SCOPUS:0034779894
SN - 0167-7764
VL - 40
SP - 171
EP - 189
JO - Journal of Atmospheric Chemistry
JF - Journal of Atmospheric Chemistry
IS - 2
M1 - 336590
ER -