Temperature-Dependent Henry’s Law and Condensation, Evaporation Rates

[boulderdaze]

The equilibrium constant for gas–particle partitioning is defined as:

K_eq = k_f / k_r

where k_f is the condensation (forward) rate constant and k_r is the evaporation (reverse) rate constant.

Use a temperature-dependent Henry’s Law Constant:

K_eq(T) = HLC(298K) * e^(C * ( 1/T - 1/298K ))

where:

• HLC(298K) is the Henry’s Law constant at 298 K
• C captures species-specific temperature dependence
• T is temperature (K)

The forward (condensation) rate constant k_f can be calculated based on the current conditions. So, the only unknown for a given set of environmental/aerosol conditions is k_r. The first equation can be rearranged to get:

k_r = k_f(T, r_eff, D_g) / K_eq(T)

where:

• r_eff is particle effective radius
• D_g is the gas-phase diffusion coefficient

Implementation:
Species need only define HLC(298K), temperature dependence C, and diffusion coefficient D_g. All rate constants (k_f, k_r) can then be calculated dynamically from the model state at each time step.

Discussion link: Correctness of henry's law, phase transfer algorithms