Extensive chemical measurements from the Mauna Loa Observatory (MLO) Photochemistry Experiment 2c (MLOPEX 2c) (April 15 to May 15, 1992) field campaign are analyzed in relation to the photochemistry, transport, and physical losses in the Pacific basin utilizing an episodic chemical transport model christened HANK. The budgets of NOy and O3 are examined in particular, as are model-measurement discrepancies in the NOy budget. For the long-lived species the bias of the simulated means (measured minus simulated divided by measured) of CO, CH4, C2H6, C3H8, O3, and NOx is less than 20%. The bias of ln (<C3H8>/<C2H6>) is less than 4%, and the modeled and measured means of C3H8 are not significantly different. H2O2, CH3OOH, and radon agree within a standard deviation. The simulated concentrations of NOy, HNO3, and peroxyacetyl nitrate (PAN) are high, while the short-lived hydrocarbons (C2H6 and C2H4) are low. Frequency distributions and species' cross correlations are also used to diagnose and evaluate the simulation. Sensitivities in the model formulation are discussed. The results indicate that the subtropics demarcate a transition between a regime characterized by Hadley cell transport to the south and one characterized by rapid isentropic mixing to the north. Vigorous photochemical processing occurs in the remote subtropical Pacific as PAN is converted to NOx, which in turn is converted to HNO3. This rapid photochemistry is related to the slope of the isentropic surfaces in the subtropics. It maintains elevated levels of NOx in the remote Pacific, reduced levels of HNO3/NOx, and increases the net ozone production. The model and measurements show that as air masses are processed photochemically (as measured by AGE) the relative concentrations of PAN and NOx decrease, as does PAN/NOy; corresponding increases occur in HNO3, HNO3/NOx, and HNO3/NOy. In both the model and measurements, H2O2, CH3OOH, and HNO3/NOx are tracers of photochemically processed air, while high concentrations of C3H8, C2H6, NOx, and PAN are associated with younger air. ¿ 2001 American Geophysical Union