Experimental Data Used to Develop the E-AIM Models


The E-AIM models are based upon a large array of different types of data which yield solute and/or water activities in aqueous solutions, and their variation with temperature. While the sources of the measurements are cited in the publications describing the development of E-AIM, they are sometimes obscure and in many cases some calculation is needed to obtain the desired thermodynamic quantity. We therefore present here the data used to parameterise the E-AIM models, for use by other scientists.

The main elements of E-AIM are: Henry's law constants of volatile components (such as HNO3 and NH3), equilibrium constants for the formation of solid phases, vapour pressures of pure water, and descriptions of the thermodynamic properties of both pure aqueous solutions (containing a single solute) and ternary mixtures (containing two solutes). The data used to characterise the properties of the aqueous phase are listed here. The tables are currently restricted to ternary mixtures.

The data have been compiled with support from ACCENT, the European Network of Excellence for Atmospheric Composition Change (an EC 6th Framework Programme), which is gratefully acknowledged.

Presentation of Data

The measurements are separated, by type, into a series of tables for each ternary sub-system. Thus, for example, for aqueous H+ - Na+ - Cl there are two tables: one for solubilities of the solid NaCl(s) in the system, and one for mean activity coefficients of HCl obtained from electromotive force measurements.

Compositions of the aqueous solutions are specified in a variety of units in the original publications describing the experiments. Here all compositions are given in mol per kg of water (molality).

Many more digits have generally been retained in the tabulated data values than are significant, where these have been converted from the original units or are thermodynamic quantities calculated from the published measurement. This avoids rounding errors, and ensures that the original data values can be recovered if needed. However, it also means that the number of digits should not be taken as an indication of the accuracy or precision of the measurement.

Different types of measurement, though yielding the same fitted quantity, can differ greatly in their accuracy and precision. For example, both isopiestic measurements and electrodynamic balance experiments can be used to obtain osmotic coefficients of solutions, but the former experiment is more accurate by a very large margin. Care should therefore be taken when using the information presented in these pages, and the original

E-AIM publications should be consulted for discussions of the data.

Other Measurements

The development of E-AIM Models I, II, and III took place between 1992 and 1997, with some further revisions as late as 2001. Results from recent work (over the last several years) may therefore not have been included in, or compared to, the models. We draw particular attention to the electrodynamic balance studies of Chan and co-workers (e.g., J. Geophys. Res. 105, D9, 11699-11709, 2000) as a source of new data. Their experiments yield water activities for supersaturated aqueous aerosols at very low relative humidities.

For most ternary systems in E-AIM Model III, data for salt solubilities in aqueous solution were compiled for a range of temperatures (not just 298.15 K). These additional data are also presented in the tables, although they were not used in the development of the model.

Model IV is the work of Friese and Ebel (J. Phys. Chem. A 114, 11595-11631, 2010), and they used many of the data compiled here.

The Systems

The ternary aqueous systems are listed below, together with the E-AIM model that they apply to (I, II, or III). Click on the system names to go to the data.

System Model     System Model     System Model
H - SO4 - NO3  I, II, III        NH4 - SO4 - Cl  III        NH4 - Na - NO3  III 
H - SO4 - Cl  I, III        NH4 - NO3 - Cl  III        NH4 - Na - Cl  III 
H - SO4 - Br  I        H - NH4 - Cl  III        Na - SO4 - NO3  III 
H - NH4 - SO4  II, III        H - Na - SO4  III        Na - SO4 - Cl  III 
H - NH4 - NO3  II, III        H - Na - NO3  III        Na - NO3 - Cl  III 
NH4 - HSO4 - NO3  II, III        H - Na - Cl  III       
NH4 - SO4 - NO3  II, III        NH4 - Na - SO4  III