In previous work, an inverse method based on the Kalman filter was used to deduce regional emissions for chlorofluorocarbons (CFC-11) in a global chemical transport model . CFC-11 has reasonably constant emissions over the years we addressed; however, most trace gases with poorly constrained global budgets (i.e. CO2, CH4, and N2O) have seasonally varying sources and sinks. The goal of this work is to explore various adaptations that exist in Kalman filter theory and to identify the optimum method for deducing time-varying sources/sinks. To make this study feasible in both computer time and cost, we utilize a simplified atmospheric chemical transport model to investigate the methodology. We test many available adaptations in Kalman filter theory and conclude that the most accurate method is to use an adaptive-iterative approach et al., 1986>. ¿ American Geophysical Union 1996