A Spectroscopic Study of Atmospherically Relevant Concentrated Aqueous Nitrate Solutions.

Concd. aq. NO3- aerosols are present in the earth atm. due to heterogeneous reactions of sea salt and mineral dust aerosol with NOx (e.g., NO2, NO3, HNO3, N2O5). Since the water content of these aerosols depends on relative humidity (RH), the compn. and NO3- concn. also depends on RH. Unlike the original aerosols, aq. NO3- aerosols are photochem. active at solar wavelengths. To better understand the NO3- chromophore in concd. aq. NO3- aerosols, the attenuated total reflection-Fourier transform IR spectroscopic (ATR-FTIR) and UV/VIS spectra of concd. NO3- solns. were measured over a large concn. range. Both ATR-FTIR and UV/VIS spectroscopy showed changes in NO3- spectra with increasing concn. Ab-initio calcns. were used to aid in assigning and interpreting these spectra. From these data, it was predicted that aq. NO3- aerosols photoreactivity will strongly depend on RH since the mol. and electronic structure of NO3- becomes increasingly perturbed from that of the isolated ion in highly concd. atmospherically-relevant solns. [on SciFinder(R)]