This paper develops a conceptual model to analyze how specific factors affect the compliance costs of three suboptimal policy instruments, when compared to the optimal ambient permit system (APS) benchmark. The model considers a non-uniformly mixed pollutant and explicitly incorporates the following factors: number of polluting sources; size, in terms of emissions, of each process; marginal abatement costs for each process; effluent concentrations; the transfer coefficient that relates emissions to environmental quality at the receptor; and the desired environmental quality target. APS is compared to a suboptimal emission permit system (EPS), and two Command and Control (CAC) policies-equal percentage reduction (PER) and a uniform effluent concentration standard (STD). The results show the importance of the different factors and their interactions in determining each policy instrument's cost-effectiveness ranking. Surprisingly, EPS performs well within the usual values of these factors and in specific cases STD and PER also perform similarly to APS.