The performance of numerical techniques in solving differential equations of the gas phase chemistry submodel (i.e., the chemical solver) is one of the most important factors in determining the overall computational cost for a three-dimensional (3-D) Air Quality Model (AQM). The estimated performance of a chemical solver in an AQM is often obtained by using simple box model analysis. In the present work some essential characteristics of the computational environment of any AQM, the operator splitting technique, have been identified and shown that different evaluation procedures will result in different conclusions for the relative performances of chemical solvers. A new box model evaluation procedure incorporating the impact of operator splitting has been designed to better mimic the true performances of various chemical solvers. Among the chemical solvers tested, the Hertel solver has the best overall performance and is the most robust in dealing with diverse computational environments. ¿ 2001 American Geophysical Union