Experiments and Simulations of Ion-Enhanced Interfacial Chemistry on Aqueous NaCl Aerosols

Abstract

A combination of experimental, molecular dynamics, and kinetics modeling studies is applied to a system of concentrated aqueous sodium chloride particles suspended in air at room temperature with ozone, irradiated at 254 nanometers to generate hydroxyl radicals. Measurements of the observed gaseous molecular chlorine product are explainable only if reactions at the air-water interface are dominant. Molecular dynamics simulations show the availability of substantial amounts of chloride ions for reaction at the interface, and quantum chemical calculations predict that in the gas phase chloride ions will strongly attract hydroxl radicals. Model extrapolation to the marine boundary layer yields daytime chlorine atom concentrations that are in good agreement with estimates based on field measurements of the decay of selected organics over the Southern Ocean and the North Atlantic. Thus, ion-enhanced interactions with gases at aqueous interfaces may play a more generalized and important role in the chemistry of concentrated inorganic salt solutions than was previously recognized.

Infrared Spectroscopy of the Microhydrated Nitrate Ions NO3−(H2O)1−6

“…-(H 2 O) 4 , simulated linear absorption spectra, and structures of four isomers are shown in Figure 5. The experimental spectrum is different from the previously discussed spectra in that band A is asymmetric and much broader (fwhm of ∼70 cm -1 ).…”

“…The lowest-energy structures (see Figure 6) for n ) 5 and 4 are similar; 5-I and 4-I both include a four-membered water ring bound to the nitrate ion. For n ) 5, the additional water molecule is doubly H-bonded to the core, 4 . Simulated spectra, derived from B3LYP2/augcc-pVDZ scaled harmonic frequencies and intensities and convoluted using a Gaussian line shape function with a fwhm of 15 cm -1 , and structures are shown for four isomers (see text).…”

“…We measure IR spectra of mass-selected nitrate-water clusters from 600 to 1800 cm -1 , the spectral region of characteristic vibrational modes of the ion and the solvent molecules, at low temperature and in the absence of a counterion. This method has proven very useful in recent studies on the microhydration of anions, for example, SO 4 2-and SF 6 -, 24-26 and on water cluster anions. 27,28 Similar to SO 4 2-, NO 3 -is of sufficiently high symmetry to support degenerate vibrational levels.…”

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

“…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.…”

Hygroscopic Growth and Deliquescence of NaCl Nanoparticles Coated with Surfactant AOT

“…1,7 The high surface-to-volume ratio of nanoparticles strongly favors atmospheric chemistry that is specific to the particle surfaces. 8,9 Atmospheric particles can significantly expand in size by taking up water as the relative humidity (RH) increases. This hygroscopic growth increases the particle's single scattering albedo and plays an important role in cloud droplet formation.…”