Estimation of aircraft turbofan engine exhaust emissions with environmental and economic aspects at a small-scale airport
Authors: Akdeniz Halil Yalcin 
Published: September 2021

Purpose
The purpose of this study is to estimate the nitrogen oxide (NOx), carbon monoxide (CO) and hydrocarbon (HC) emissions and their environmental and economic aspects during the actual landing and take-off operations (LTO) of domestic and international flights at a small-scale airport. In this regard, the aircraft-induced NOx, CO and HC emissions analyses, the global warming potential (GWP) estimations of exhaust emissions and the life cycle assessment (LCA)-based environmental impact (EI) estimations of exhaust emissions, and the eco-cost estimation of exhaust emissions are measured.

Design/methodology/approach
Estimations and calculations are performed in parallel with the International Civil Aviation Organisation’s Engine Emission Databank and Intergovernmental Panel on Climate Change approaches. Also, to assess the environmental effect of the pollutants, the GWP and the EI analyses which is based on the LCA approaches are used. Finally, the eco-cost approach has been used to discuss the economic aspects of these emissions.

Findings
The total emissions of air pollutants from aircraft are estimated as 601.067 kg/y for HC, 6,074.905 kg/y for CO and 4,156.391 kg/y for NOx at the airport. Also, emissions from international flights account for 79% of emissions from all flights. The Airbus A321 type of aircraft has accounted for more than half of the total HC, CO and NOx emissions. The total amount of emissions from the B738 type of aircraft is estimated as 24%. It is noticed that the taxi phase constitutes 52% of the total HC, CO and NOx emissions. Because of this, it is selected the five different alternative taxi times to observe the effects of pollution role of taxiing time in detail and re-estimated accordingly. According to the re-estimated results with variations in taxiing time, when the taxiing time at the airport is 24 min instead of the original value, this case contributes to a decrease in total LTO emissions of approximately 4%. Also, when the taxiing time is decreased by 2 min, HC, CO and NOx emission amounts decrease by approximately 3.9%, 5.9% and 1.2%, respectively. At this point, the polluting role of taxiing time will be helpful to reduce the aircraft-induced HC, CO and NOx emissions for other larger-scale airports. On the other hand, it is estimated that the GWP of the A321 is 1,066.29 t CO2e whilst the GWP of B738 is 719.50 t CO2e. The eco-cost values of the A321, B738, A320 and CL60-type of aircraft are estimated as almost 61,049.42, 41,086.02, 18,417.43 and 6,163.59 Euros, respectively.

Practical implications
With the detailed results of this study, the polluting role of taxiing time on total HC, CO and NOx emissions in a small-scale airport will be helpful to reduce aircraft-induced emissions for other larger-scale airports. Also, in the future, this study and its results will be helpful to create an emission inventory at the airport examined.

Originality/value
In this study, different from some previous studies, air pollutants from aircrafts are evaluated with different aspects such as the EI and eco-cost and GWP. Also, this study will be making a helpful contribution to the literature as it covers the more diversity of the different types of aircrafts in the analyses.