Determination of Henry's Law Constants by Equilibrium Partitioning in a Closed System Using a New in Situ Optical Absorbance Method

Abstract

Abstract-A new method for measurement of thermodynamic Henry's law constants (H) is reported. In this method, the optical absorbance of a dilute aqueous solution containing an organic compound is followed with time as the compound partitions into the air above the solution in a sealed vessel. The change in optical absorbance (i.e., change in concentration) and the vapor to liquid volume ratio of the vessel are then used to calculate the value for H. The concentration of the organic compound in the aqueous and vapor phases need not be known. This method allows the approach to equilibrium to be observed in real time so that attainment of equilibrium is readily apparent. This method works particularly well for water-soluble compounds having low vapor pressures. The applicability of this method is limited to compounds that exhibit significant optical absorbance in the ultraviolet and visible regions of the electromagnetic spectrum. Values for H and their temperature dependencies measured using this new method are reported for methacrolein, methyl vinyl ketone, benzaldehyde, and acetophenone. Values for H are also reported for benzene, toluene, and ethylbenzene at 298 K. All reported H data are compared with previously reported values.

Aqueous-phase ozonolysis of methacrolein and methyl vinyl ketone: a potentially important source of atmospheric aqueous oxidants

“…Iraci et al (1999) estimated that only 0.02% of the total amount of MAC and 0.1% of the total amount of MVK enter the aqueous phase under a condition of gas-aqueous partition equilibrium at 298 K, based on the Henry constants of the compounds (i.e. 6.5 M atm −1 for MAC and 41 M atm −1 for MVK, Allen et al, 1998;Iraci et al, 1999), choosing 1×10 −6 cm −3 H 2 O/cm 3 air (1 g H 2 O/cm 3 ) as a generous estimate of cloud liquid water content (Pruppacher and Klett, 1997). According to this arithmetic, it can be estimated that only 0.00004% of the total isoprene present will reside in the aqueous phase at 298 K, based on its Henry constant of 1.3×10 −2 M atm −1 at this temperature (Allen et al, 1998).…”

“…6.5 M atm −1 for MAC and 41 M atm −1 for MVK, Allen et al, 1998;Iraci et al, 1999), choosing 1×10 −6 cm −3 H 2 O/cm 3 air (1 g H 2 O/cm 3 ) as a generous estimate of cloud liquid water content (Pruppacher and Klett, 1997). According to this arithmetic, it can be estimated that only 0.00004% of the total isoprene present will reside in the aqueous phase at 298 K, based on its Henry constant of 1.3×10 −2 M atm −1 at this temperature (Allen et al, 1998). If this ratio were combined with the global isoprene emission flux of 625 Tg yr −1 , the amount of SOA derived from the aqueous-phase reaction of isoprene would be only 0.00025 Tg yr −1 , even though isoprene molecules partitioning in the aqueous phase are completely transformed into SOA.…”

Effect of membrane on carbonation and carbon dioxide uptake ofChlorellasp.

“…In overall, Figure 2 shows that carbonic acid increased with CO2 feed. It was found that CO2 conversion to carbonic acid agreed with Henry's law statement whereas the equilibrium constant of carbonic acid in water is approximated at 1.7 x 10 -3 at room temperature [26]. Most of the CO2 gas remains as CO2 in water.…”

Formation of aqueous-phase α-hydroxyhydroperoxides (α-HHP): potential atmospheric impacts

“…To examine potential evaporation of carbonyls and OH generation from H 2 O 2 photolysis, some methacrolein samples were analysed a second time 10 h after the first measurement. Methacrolein was chosen because it is the most volatile aldehyde studied here (Allen et al, 1998) and is highly reactive to OH radicals (Herrmann et al, 2010). The concentration of methacrolein did not show observable change before and after 10 h of room light exposure, and so it is assumed that evaporative loss and room-light exposure induced negligible effects to other samples as well.…”

“…The aldehyde species studied here span a wide range of water solubility. Specifically, the aqueous-phase concentrations of volatile species such as acetaldehyde, propionaldehyde, and methacrolein, whose K H values are typically below 20 M atm −1 (Zhou and Mopper, 1990;Allen et al, 1998), are expected to be low. However, aqueous-phase concentrations of highly water-soluble aldehydes, such as glycolaldehyde, methylglyoxal, and glyoxal can be substantial.…”