Issue 48, 2015

The effect of cations on NO2 production from the photolysis of aqueous thin water films of nitrate salts

Abstract

The photochemistry of nitrate ions in bulk aqueous solution is well known, yet recent evidence suggests that the photolysis of nitrate may be more efficient at the air–water interface. Whether and how this surface enhancement is altered by the presence of different cations is not known. In the present studies, thin aqueous films of nitrate salts with different cations were deposited on the walls of a Teflon chamber and irradiated with 311 nm light at 298 K. The films were generated by nebulizing aqueous 0.5 M solutions of the nitrate salts and the generation of gas-phase NO2 was monitored with time. The nitrate salts fall into three groups based on their observed rate of NO2 formation (RNO2): (1) RbNO3 and KNO3, which readily produce NO2 (RNO2 > 3 ppb min−1), (2) Ca(NO3)2, which produces NO2 more slowly (RNO2 < 1 ppb min−1), and (3) Mg(NO3)2 and NaNO3, which lie between the other two groups. Neither differences in the UV-visible spectra of the nitrate salt solutions nor the results of bulk-phase photolysis studies could explain the differences in the rates of NO2 production between these three groups. These experimental results, combined with some insights from previous molecular dynamic simulations and vibrational sum frequency generation studies, show that cations may impact the concentration of nitrate ions in the interface region, thereby directly impacting the effective quantum yields for nitrate ions.

Graphical abstract: The effect of cations on NO2 production from the photolysis of aqueous thin water films of nitrate salts

Supplementary files

Article information

Article type
Paper
Submitted
06 Sep 2015
Accepted
12 Nov 2015
First published
12 Nov 2015

Phys. Chem. Chem. Phys., 2015,17, 32211-32218

Author version available

The effect of cations on NO2 production from the photolysis of aqueous thin water films of nitrate salts

N. K. Richards-Henderson, C. Anderson, C. Anastasio and B. J. Finlayson-Pitts, Phys. Chem. Chem. Phys., 2015, 17, 32211 DOI: 10.1039/C5CP05325K

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