Solubilities of pyruvic acid and the lower (C₁-C₆) carboxylic acids. Experimental determination of equilibrium vapour pressures above pure aqueous and salt solutions

Henry's law constants K′_H (mol kg^-1 atm^-1) have been determined at 298.15 K for the following organic acids: formic acid (5.53±0.27×10³); acetic acid (5.50±0.29×10³); propionic acid (5.71±0.34×10³);n-butyric acid (4.73±0.18×10³); isobutyric acid (1.13±0.12×10³); isovaleric acid (1.20±0.11×10³) and neovaleric acid (0.353±0.04×10³). They have also been determined from T=278.15 K to T=308.15 K for n-valeric acid (ln(K′_H)=-14.3371+6582.96/T);n-caproic acid (ln(K′_H)=-13.9424+6303.73/T) and pyruvic acid (ln(K′_H)=-4.41706+5087.92/T). The influence of 9 salts on the solubility of pyruvic acid at 298.15 K has been measured. Pyruvic acid is soluble enough to partition strongly into aqueous atmospheric aerosols. Other acids require around 1 g of liquid water m^-3 (typical of clouds) to partition significantly into the aqueous phase. The degree of partitioning is sensitive to temperature. Considering solubility and dissociation (to formate) alone, the ratio of formic acid to acetic acid in liquid water in the atmosphere (at equilibrium with the gas phase acids) is expected to increase with rising pH, but show little variation with temperature. © 1995 Kluwer Academic Publishers.