Gas-Liquid-Equilibrium

Basic Henry's law equilibrium at fixed temperature (Seinfeld & Pandis 2006, Chapter 7, Eq. 7.3). Computes the aqueous-phase concentration C_aq = H_A × p_A, where H_A is the Henry's law constant at the reference temperature and p_A is the gas-phase partial pressure of species A. Migrated from Aerosol.jl src/henrys_law.jl `HenrysLaw` (esm-3ro).