Air Transportation contributes in more than 2% of the total global emissions. In this paper, we formulate the air traffic flow management (ATFM) problem as a bi-objective mixed integer linear programming model that minimizes the carbon dioxide (CO 2) emissions and the total delay cost. The model is solved using a Pareto-based scalarization technique called the weighted comprehensive criterion method. A numerical example is used to illustrate the effect of considering CO 2 emissions on the ATFM network. A Pareto front is developed to illustrate the trade-off between CO 2 emissions and the total delay costs. The results showed that reducing 1 kg of CO 2 emissions comes at a delay cost of 1.22 €. This result can be beneficial for decision makers in determining penalty values and setting aviation emission policies.