Abstract
Several time-integrated and time-resolved experiments have been performed on different sodium-containing dry aerosols in air to investigate the behavior of atomic sodium emission at the yellow doublet after photofragmentation with 193 nm photons provided by an ArF excimer laser. It is shown that sodium chloride, sodium hydroxide, and especially sodium sulfate require different thresholds for the overall process of vaporization, dissociation, and excitation of atomic emission. This can be clearly seen by the experimental fact that (1) the onset of the time-integrated emission signal starts at different laser energies, and (2) the time-resolved shapes of the emission signal during the laser pulse (13 ns) are markedly different in the case of chloride and sulfate aerosols, the former rising faster than the latter. From an analytical point of view, the detection limit for sodium in airborne particles is 0.3 ng of sodium per gram of air (∼ 0.017 ppbv), which is about one order of magnitude better than the detection limit reported by early laser-induced plasma experiments.
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