Research at TU Delft shows most nitrogen deposition from aviation comes from high altitude
Aircraft emit nitrogen oxides and other emissions during both the LTO-phase (taxiing, take-off and landing) and when flying at high altitudes. These emissions return to the ground, resulting in nitrogen deposited over land and water bodies. Using an atmospheric model, researchers at TU Delft have quantified – for the first time – that in 2019 aviation was responsible for just under 1.2% of total global nitrogen deposition from all sources (anthropogenic and natural). However, aviation’s impacts did grow by as much as 72% between 2005 and 2019. The researchers also calculated that, on average, 92% of aviation-induced nitrogen deposition is due to emissions during high-altitude flight, the majority of which is cruise. This research does not specifically zoom into the emissions from Dutch aviation or Schiphol Airport causing nitrogen deposition in Dutch Natura 2000 areas. It does show that to comprehensively address the nitrogen deposition from aviation worldwide, a global approach is needed that takes into account the cross-border nature of the impacts, similarly to other atmospheric effects of aviation such as air pollution and climate. The research has now been published in the journal Science of the Total Environment.
Aviation emissions lead to nitrogen deposition on land
Part of the nitrogen deposition on land is caused by aviation. Assistant Professor of the Atmospheric Impacts of Aviation, Dr. Irene Dedoussi, who led the study: “In order to be able to reduce this adverse environmental effect, for example to protect vulnerable natural areas, it is necessary to know where the emissions from aviation take place, how they spread and chemically react, where these pollutants are subsequently deposited on the ground and in what form.” The team, in addition to Dr. Dedoussi, consisting of PhD candidate Flávio D.A. Quadros, MSc, alumnus Marijn van Loo, MSc, and Prof.Dr. Mirjam Snellen, used an atmospheric chemistry-transport model to calculate which part of global nitrogen deposition can be attributed to aviation emissions. This is the first study to look at the big picture. Thus, in addition to emissions from the flight phase of landing, taxiing and take-off, the researchers also include emissions during high altitude flight (climb, cruise and descent) in their calculations. They also look at the form in which nitrogen is deposited. They calculated these contributions for two years: 2005 and 2019.
By far most of the nitrogen deposition come from flights at high altitude:
In 2019, aviation was responsible for 1.39 Tg of nitrogen deposited worldwide. On average, that is just under 1.2% of total global nitrogen deposition caused by all sources. The exact share varies: over Asia it is 0.66%, over Europe 1.13% and over North America 1.61%.
The research data shows that between 2005 and 2019 global nitrogen deposition from all sources (including aviation) increased by 2.4%. The nitrogen deposition from aviation specifically grew by 72% between these two years, in line with the growth of aviation emissions over that period.
On average, 92% of nitrogen deposition is due to emissions during high-altitude flight (climb, cruise and descent). Emissions during the landing, taxi and take-off phase of flight (LTO) account for an average of 8% of nitrogen deposition from aviation worldwide. This also varies: in regions with high aviation activity, the LTO share is higher: between 16% and 32%.
The resulting nitrogen deposition occurs over a wide area. Large quantities of nitrogen end up in areas with a lot of aviation activity, such as the coastal areas of the US, Europe and East Asia. But a lot of nitrogen is also deposited on areas far from where emissions occurred, e.g. in areas in the dominant wind direction or in areas with heavy rainfall.
56% of deposition due to aviation occurs over water.
In 2019, aviation was on average responsible for <1.0% of total nitrogen deposition in Natura 2000 areas. More research is needed, however, as the scale of the global model the researchers used (resolution of ~25-55 km across Europe) is too global to zoom in on the specific spatial features of these areas.
Taking into account the long lifetime of current aircraft and an expected global growth of aviation in the coming decades, the share of aviation in nitrogen deposition will further increase. The researchers expect that the use of sustainable aviation fuels will not significantly change this.
Intercontinental nature of the problem
The study by Flávio D.A. Quadros, MSc, Marijn van Loo, MSc, Prof.Dr. Mirjam Snellen and Dr Irene C. Dedoussi gives guidance to policymakers who want to reduce nitrogen deposition, looking at the responsibility of sectors. Dedoussi notes: “Current policy efforts to curb nitrogen deposition from aviation often focus on emissions that occur during the LTO flight phases, near airports. This research shows that the majority of aviation’s deposition globally comes from emissions at higher altitudes, which can lead to spatially widespread impacts far away. That’s not very surprising, since it’s a similar case for aviation’s air pollution and climate impacts.”