Reactive Uptake of Cl2(g) and Br2(g) by Aqueous Surfaces as a Function of Br- and I- Ion Concentration: The Effect of Chemical Reaction at the Interface

229

272

Section: Chemistry At the Interface Of Sea Salt Particlesmentioning

confidence: 99%

Reactions at surfaces in the atmosphere: integration of experiments and theory as necessary (but not necessarily sufficient) for predicting the physical chemistry of aerosols

Finlayson-Pitts

2009

229

272

“…1 However, a combination of computational [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] and experimental studies [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] has shown that ions can reside and even be enhanced at the interface.…”

Section: Introductionmentioning

confidence: 99%

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

Richards-Henderson

Anderson

Anastasio

et al. 2015

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 NO 2 was monitored with time. The nitrate salts fall into three groups based on their observed rate of NO 2 formation (R NO 2 ): (1) RbNO 3 and KNO 3 , which readily produce NO 2 (R NO 2 4 3 ppb min À1 ), (2) Ca(NO 3 ) 2 , which produces NO 2 more slowly (R NO 2 o 1 ppb min À1 ), and (3) Mg(NO 3 ) 2 and NaNO 3 , 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 NO 2 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.

“…Altmaier et al 109 have shown that Mg(OH) 2 reacts to form the Mg 2 (OH) 3 Cl Á 4H 2 O (hydroxychloride) in magnesium chloride solutions with concentrations greater than 2 molal. The K sp for magnesium hydroxide is 1.25 Â 10 À11 at 25 1C.…”

Section: Resultsmentioning

confidence: 99%

“…The concentrations of the gas phase species were calculated using a numerical integration program, Acuchem. 102 Except for the photolysis rate constants (k p ) for O 3 and H 2 O 2 , all of the gas phase rate constants are known. 103,104 The value of k p for O 3 was determined in independent static experiments in which the loss of O 3 during photolysis in the DRIFTS cell was followed at 47% RH using its gas phase absorbance at 1028 cm À1 .…”

Section: Methodsmentioning

confidence: 99%

“…16 For example, for large (B10 mm) size particles, the falling droplet apparatus has been used extensively to study gas uptake and reaction. 1,3,13,17,18 FTIR studies of smaller particles have been carried out at relatively high particle concentrations; [19][20][21][22] following the particles with time using this method is complicated by continuously changing particle size distributions due to coagulation and settling of the particles. 23,24 A new technique is optical levitation of single droplets combined with Raman spectroscopy, but this has only been applied to relatively few systems to date.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A new approach to studying aqueous reactions using diffuse reflectance infrared Fourier transform spectrometry: application to the uptake and oxidation of SO2 on OH-processed model sea salt aerosol

Shaka

Robertson

Finlayson-Pitts

2007

A new approach to studying aqueous reactions using diffuse reflectance infrared Fourier transform spectrometry: application to the uptake and oxidation of SO2 on OH-processed model sea salt aerosol. Diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) is a powerful technique for analyzing solid powders and for following their reactions in real time. We demonstrate that it can also be applied to studying the uptake and reactions of gases in liquid films. Within the DRIFTS cell, a 10% (w/w) mixture of MgCl 2 Á 6H 2 O in NaCl was equilibrated with air at 50% RH, which is above the deliquescence point of the magnesium salt but below that of NaCl. This mixture of NaCl coated with an aqueous magnesium chloride solution was then reacted with gas phase OH to generate hydroxide ions via a previously identified interface reaction. This treatment, hereafter referred to as OH-processing, was sufficient to convert some of the magnesium chloride to Mg(OH) 2 and Mg 2 (OH) 3 Cl Á 4H 2 O, making the aqueous film basic and providing a reservoir of alkalinity. Subsequent addition of SO 2 to the basic processed mixture resulted in its uptake and conversion to sulfite which was measured by FTIR. The sulfite was simultaneously oxidized to sulfate by HOCl/OCl À that was formed in the initial OH-processing of the salt. Further uptake and oxidation of SO 2 in the aqueous film took place when the salt was subsequently exposed to O 3 . These studies demonstrate that DRIFTS can be used to study the chemistry in liquid films in real time, and are consistent with the hypothesis that the reaction of gaseous OH with chloride ions generates alkalinity that enhances the uptake and oxidation of SO 2 under these laboratory conditions.