Using the GREET model, the estimation technique accounts for the direct and indirect emissions, including air pollutants such as nitrogen oxides and carbon monoxide. The GREET model takes into account the fuel consumption and engine efficiency of the vehicle. It’s pertinent to know that real-world conditions can vary significantly from the assumptions used in the model. For this reason, actual emissions may be higher or lower than what is predicted by GREET. The model provides a good starting point for understanding and estimating emissions from transportation.