Table 1.

Comparison of cloud chemistry models included in CMAQv5.1.

Process	AQCHEM standard	AQCHEM - KMT	AQCHEM - KMTI
Solver	Forward Euler	Rodas3 (Rosenbrock)	Rodas3 (Rosenbrock)
Gas-aqueous mass transfer	Henry’s law equilibrium	Kinetic mass transfer with gas diffusion/interfacial limitation	Kinetic mass transfer with gas diffusion/interfacial limitation
Ionic dissociation	Equilibrium	Forward/reverse reactions	Forward/reverse reactions
Chemistry	5 SO2 to ${\text{SO}}_4^{2-}$ oxidation reactions + 2 SOA-forming reactions from glyoxal and methylglyoxal	Same mechanism as AQCHEM (includes aqueous diffusion correction for O3)	AQCHEM mechanism + IEPOX/MPAN chemistry (includes aqueous diffusion correction for O3, and IEPOX/MPAN)
pH	[H+ ] estimated at each time step using a bisection method while maintaining electroneutrality	Dynamic [H+] (initial value is based on activated aerosol ions at t = 0 assuming electroneutrality)	Dynamic [H+] (initial value is based on activated aerosol ions at t = 0 assuming electroneutrality)
Other	Instantaneous activation of all accumulation- and coarse-mode species	Instantaneous activation of all accumulation- and coarse-mode species	Instantaneous activation of all accumulation- and coarse-mode species