A laser-photolysis, fragment- fluorescence method (47) and an active chemical ionization, mass spectrometric technique (48) were recently reported for this species. These studies clearly indicate that the intercompared techniques do not allow the unequivocal determination of nitric acid in the atmosphere. The intercomparisons found differences of the order of a factor of 2 generally, and up to at least a factor of 5 at levels below 0.2 ppbv. These equilibria can be disturbed by the sampling process these disturbances lead to negative or positive errors in the determination of the ambient vapor-phase concentration. The in situ measurement of this species has proven difficult because it very rapidly absorbs on any inlet surfaces and because it is involved in reversible solid-vapor equilibria with aerosol nitrate species. Several formal and informal intercomparisons of nitric acid measurement techniques have been carried out (43-46) these intercomparisons involve a multitude of techniques. One can also consider the liquid/vapor equilibria in a simple (c = 1) two- phase system with /Xvap 7 liq. Note 1 An alternative definition of critical solution point refers strictly to liquid-vapor equilibria. (1948) Densities and liquid-vapor equilibria of the system ethanol-isooctane (2,2,4-trimethylpentane) between 0 and 50°. Kretschmer, C.B., Nowakowska, J., Wiebe, R. Liquid-Vapor Equilibria using the Wang-Landau Algorithm. The liquid -vapor equilibria, along the vaporization curve is expressed as.
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