Raman spectroscopy and atomic force microscopy of the reaction of sulfuricacid with sodium chloride

The reaction of NaCl with H2SO4 is investigated using Raman spectroscopy; a tomic force microscopy (AFM), and gravimetric analysis. Raman spectra are c onsistent with the formation of NaHSO4 with no evidence for Na2SO4. The spe ctra indicate that the phase of NaHSO4 varies with the amount of H2O in the H2SO4 At low H2O concentrations, the reaction produces anhydrous beta -NaH SO4, which undergoes a phase change to anhydrous alpha -NaHSO4 over the cou rse of 18 h. At higher H2O concentrations, anhydrous alpha -NaHSO4 is forme d with small amounts of NaHSO4 H2O. AFM measurements on NaCl (100) show the formation of two distinct types of NaHSO4 structures consistent in shape w ith alpha -NaHSO4 and beta -NaHSO4. The beta -NaHSO4 structures are mobile and move along the NaCl (110) plane until they encounter existing stationar y alpha -NaHSO4 structures whereupon the two forms coalescence to form larg er alpha -NaHSO4 structures. Gravimetry was used to determine the amount of HCl evolved upon exposure to aqueous H2SO4 solutions modeling atmospheric aerosols. At low H2SO4 concentrations, a large percentage of the HCl formed remains dissolved in the H2O. These results indicate that for conditions s imulating relative humidities above 40%, the fraction of HCl released from this reaction may be as low as 0.40 +/- 0.11.