Effective Henry's Law Constants Research Articles

Investigation of the heterogeneous NO2 conversion on perchloric acid surfaces

The heterogeneous conversion of NO2 on perchloric acid surfaces into HONO, HNO3 and N2O was investigated in a bubbler system under simulated atmospheric conditions. NO2, HONO and N2O were monitored time resolved by long-path tunable infrared diode laser absorption spectrometry using single vibrational rotational lines. The experimental results show that NO2 is heterogeneously converted on acid surfaces into HONO and consecutively into N2O. HONO formation in the reaction system occurs by the heterogeneous reaction of NO2 with water. The solubility of HONO in perchloric acid was determined at 298 K as a function of the acid concentration. The effective Henry's law constant (KHeff) is well described by:

Solubility of HOCl in water and aqueous H2SO4 to stratospheric temperatures

Henry's law constants K′H (mol kg−1 atm−1) for the reaction HOCl(g)=HOCl(aq) near room temperature, literature data for the associated enthalpy change, and solubilities of HOCl in aqueous H2SO4 (46 to 60 wt%) at temperatures relevant to the stratosphere (200 K≤T≤230 K) are shown to be thermodynamically consistent. Effective Henry's law constants [H*=mHOCl/pHOCl, in mol kg−1 atm−1] of HOCl in aqueous H2SO4 are given by: ln(H*)=6.4946−mH2SO4(−0.04107+54.56/T)−5862 (1/To−1/T) where T(K) is temperature and To=298.15K. The activity coefficient of HOCl in aqueous H2SO4 has a simple Setchenow-type dependence upon H2SO4 molality.

Solubility of HCL in sulfuric acid at stratospheric temperatures

The solubility of HCl in sulfuric acid was measured using a Knudsen cell technique. Effective Henry's law constants are reported for sulfuric acid concentrations between 50 and 60 weight percent and for temperatures between 220 and 230 K. The measured values indicate that very little HCl will be dissolved in the stratospheric sulfate aerosol particles.

Effective henry's law constants for free chlorine and free bromine

Volatilization represents a non-reactive loss mechanism for aqueous halogen biocides. Equilibrium volatilities, as measured by effective Henry's law constants, or effective dimensionless partition coefficients ( m), for free chlorine and free bromine were estimated to be 0.0604 atm ( m = 4.55 × 10 −5) and 0.0293 atm ( m = 2.21 × 10 −5), respectively, at 20°C using a stripping column. A true Henry's constant of 0.0600 atm ( m = 4.52 × 10 −5) was estimated for HOCl by application of equilibrium data to the system. The effective Henry's constant for free chlorine ( H Cl) is comparable to a previously published value determined under similar conditions. Prior to this investigation, no published values for a free bromine effective Henry's constant ( H Br ) were available.

The partitioning of ketones between the gas and aqueous phases

Most ketones are not significantly hydrated; they therefore retain their chromophore and they could be photolytically degraded in solution yielding a variety of products including carboxylic acids, aldehydes and radicals. It is difficult to accurately model the partitioning of ketones between the gas phase and aqueous phase because of the lack suitable estimates of the Henry's Law constants; consequently the fate and environmental effects of ketones cannot be confidently predicted. Here we report the experimental determination of the Henry's Law constants of a series of ketones that has yielded a simple straight line equation to predict the Henry's Law constants of simple aliphatic ketones: log H∗ =0.23Σσ∗ + 1.51; where H∗ is the effective Henry's Law constant (M atm−1, and Σσ∗ is the Taft polar substituents constants. The results for 25°C are (M atm−1) CH3COCH3, 32; C6H5COCH3, 110; CH2ClCOCH3, 59; CH3COCOCH3, 74; CF3COCH3, 138. Acetophenone appears to have an abnormally high H∗. Most low molecular weight aliphatic ketones are predicted to characterized by H∗⩾30 M atm−1 and therefore they are expected to be found in the aqueous phase at concentrations of ⩾5 − 0.5 μM (given a typical gas-phase concentration range of 1–10 ppbv). The expected rate of decomposition of ketones due to photolysis in hydrometers is briefly discussed.

Parameterization of surface resistances to gaseous dry deposition in regional-scale numerical models

Methods for estimating the dry deposition velocities of atmospheric gases in the U.S. and surrounding areas have been improved and incorporated into a revised computer code module for use in numerical models of atmospheric transport and deposition of pollutants over regional scales. The key improvement is the computation of bulk surface resistances along three distinct pathways of mass transfer to sites of deposition at the upper portions of vegetative canopies or structures, the lower portions, and the ground (or water surface). This approach replaces the previous technique of providing simple look-up tables of bulk surface resistances. With the surface resistances divided explicitly into distinct pathways, the bulk surface resistances for a large number of gases in addition to those usually addressed in acid deposition models (SO 2,O 3, NO x and HNO 3) can be computed, if estimates of the effective Henry's Law constants and appropriate measures of the chemical reactivity of the various substances are known. This has been accomplished successfully for H 2O 2, HCHO, CH 3CHO (to represent other aldehydes), CH 3O 2H (to represent organic peroxides), CH 3C(O)O 2H, HCOOH (to represent organic acids), NH 3, CH 3C(O)O 2NO 2 and HNO 2. Other factors considered include surface temperature, stomatal response to environmental parameters, the wetting of surfaces by dew and rain, and the covering of surfaces by snow. Surface emission of gases and variations of uptake characteristics by individual plant species within the landuse types are not considered explicitly.