Global passenger air traffic has doubled in the 13 years prior to 2019, and is expected to double again over the next 20 years or so. Growing demand for aviation is met by a corresponding increase in jet fuel being burned by aircraft, releasing multiple pollutants into the atmosphere. Besides disturbing the Earth’s radiative balance, these emissions also lead to excessive deposition of reactive nitrogen, and to a degradation of air quality. Anthropogenic nitrogen deposition damages vulnerable ecosystems, while degraded air quality is associated with increases in human mortality rates. These last two environmental impacts can be very localized, but, owing to the high altitude of emissions, they also occur over intercontinental distances. This thesis aims to evaluate the magnitude of air quality and nitrogen deposition due to emissions from civil fixed-wing aircraft at a global scale, and how these impacts might change in the coming decades.@en

Excess nitrogen deposition from anthropogenic sources of atmospheric emissions, such as agriculture and transportation, can have negative effects on natural environments. Designing effective conservation efforts requires knowledge of the contribution of individual sectors. This study utilizes a global atmospheric chemistry-transport model to quantify, for the first time, the contribution of global aviation NO_x emissions to nitrogen deposition for 2005 and 2019. We find that aviation led to an additional 1.39 Tg of nitrogen deposited globally in 2019, up 72 % from 2005, with 67 % of each year's total occurring through wet deposition. In 2019, aviation was responsible for an average of 0.66 %, 1.13 %, and 1.61 % of modeled nitrogen deposition from all sources over Asia, Europe, and North America, respectively. These impacts are spatially widespread, with 56 % of deposition occurring over water. Emissions during the landing, taxi and takeoff (LTO) phases of flight are responsible for 8 % of aviation's nitrogen deposition impacts on average globally, and between 16 and 32 % over most land in regions with high aviation activity. Despite currently representing less than 1.2 % of nitrogen deposition globally, further growth of aviation emissions would result in increases in aviation's contribution to nitrogen deposition and associated critical loads.

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Aircraft emitted oxides of nitrogen (NOx) contribute both to climate change and air quality degradation. The trend of higher gas temperatures, caused by engine design choices seeking lower fuel consumption and achieve more complete combustion, has the adverse effect of increasing NOx formation, which might however be compensated by improved combustor designs. The tradeoff between lowering NOx or CO¬2 emissions is an important consideration in mitigating the environmental impacts of aviation, and, and in context of the industry’s environmental targets and forecasts, quantifying the technological trend taking place can provide an indication of future emission totals. In this study, we estimate bottom-up global fleet average aviation fuel burn and NOx emissions for the years 2005 and 2018 and extrapolate their totals to 2030, 2040, and 2045 with current air traffic and engine performance forecasts. Average NOx emission indices are evaluated for different aircraft classes at each year considered, and their changes over time are discussed together with a sensitivity analysis on the assumptions made.@en

Aviation is a growing source of atmospheric emissions impacting the Earth’s climate and air quality. Comprehensive assessments of the environmental impact of this industry require up-to-date, spatially resolved, and speciated emissions inventories. We develop and evaluate the first such estimate of global emissions from aircraft operations for the years 2017–2020. Aircraft activity data, based on flights registered by networks of aircraft Automatic Dependent Surveillance–Broadcast (ADS-B) telemetry receivers, are used together with the Base of Aircraft Data (BADA) 3.15 aircraft performance model and the International Civil Aviation Organization Engine Emissions Databank to estimate spatially resolved fuel burn and emissions of CO2, H2O, NOx (NO+NO2), SOx (SO2+SO2−4), CO, unburnt hydrocarbons (HC), and nonvolatile particulate matter (nvPM). We calculate that 937 Tg of CO2 and 4.62 Tg of NOx were emitted by aircraft in 2019, and quantify the evolution of the fleet average emission indices over time. Owing to impacts from COVID-19, we estimate a 48% lower fuel burn, resulting in 463 Tg less CO2 and 2.29 Tg less NOx emitted in 2020 than what would be otherwise expected. We conclude that ADS-B is a viable source of data to generate global emissions estimates in a timely and transparent manner for monitoring and assessing aviation’s atmospheric impacts.@en

Emissions from civil aviation degrade air quality, and have been estimated to lead to ~16 000 premature deaths annually. Previous studies have indicated that aviation emissions in different regions have varying corresponding air quality and human health impacts. Given the global nature of aviation activity and its forecasted regionally heterogeneous growth, this phenomenon poses challenges in aviation air quality decision making. In this study, we quantify the differences in the regional air quality responses to aviation emissions, and analyze their drivers. Specifically, we use the GEOS-Chem atmospheric chemistry-transport model to quantify the regional fine particulate matter (PM2.5) and ozone sensitivity to aviation emissions over Asia, Europe, and North America for 2005. Simulations with perturbed regional aviation emissions are used to isolate health impacts of increases in aviation emissions originating from and occurring in different regions. Health impacts are evaluated as premature mortality attributed to both landing and takeoff and cruise emissions. We find that the sensitivity of PM2.5 global population exposure to full-flight emissions over Europe is 57% and 65% higher than those to emissions over Asia and North America, respectively. Additionally, the sensitivity of ozone global population exposure to aviation emissions over Europe is larger than to emissions over Asia (32%) and North America (36%). As a result, a unit of fuel burn mass over Europe results in 45% and 50% higher global health impacts than a unit of fuel burn mass over Asia and North America, respectively. Overall, we find that 73% and 88% of health impacts from aviation emissions over Europe and North America, respectively, occur outside the region of emission. These results suggest that inter-regional effects and differences in regional response to emissions should be taken into account when considering policies to mitigate air quality impacts from aviation, given the projected spatially heterogeneous growth in air transportation.@en

Emissions from civil aviation traffic degrade air quality, causing human health problems that have been estimated to result in ~16 000 premature deaths per year globally, potentially making the cost to society of the air quality impacts even greater than the cost of the climate impact of these emissions. Previous studies have indicated that aviation emissions in specific areas can have impacts of significantly different intensities due to variations in population density and background atmospheric composition. We use the GEOS-Chem global atmospheric chemistry-transport model to investigate the air quality sensitivity to aviation emissions in different regions of the world by performing simulations with increased emissions on different locations at a time and comparing the resulting changes in human exposure to air pollutants (fine particulate matter and ozone). We evaluate the impacts of both landing and take-off (LTO) and cruise level emissions. The simulations are used to investigate the drivers of the differences in air quality sensitivity to emission location, shedding light to the previously observed indications that European air traffic leads to more premature deaths per mass of emissions than North American air traffic. These regionally varying air quality effects imply that regionally non-uniform regulations, if feasible, might provide efficient strategies of mitigating costs associated with air quality impacts. @en