Aircraft emissions could double air pollution deaths by 2040

Study: Global air quality and human health impacts of growing aircraft emissions. Image Credit: ChatGPT / OpenAI

Researchers quantified the current and future global health impact of aviation-related air pollution by modeling aircraft emissions under multiple scenarios and estimating their effects on mortality.

The study was published as an 'Article in Press' in the journal Communications Earth & Environment and authored by Flávio D. A. Quadros, Rick Nelen, Mirjam Snellen, and Irene C. Dedoussi, researchers affiliated with Delft University of Technology and the University of Cambridge.

Aviation Emissions: Trends, Impacts, and Assessment Challenges

Aircraft emissions contribute to climate change, nitrogen deposition, and air quality degradation, primarily by increasing concentrations of fine particulate matter (PM2.5) and ozone. These pollutants are linked to substantial public health impacts, with estimated annual mortality ranging from hundreds to tens of thousands.

In recent decades, global jet fuel consumption has increased by 3-4% annually, intensifying environmental pressures. While the aviation sector has set ambitious targets for carbon neutrality by 2050, achieving these goals largely depends on sustainable aviation fuels, which do not substantially reduce nitrogen oxides (NOx) emissions. Given that NOx is the main contributor to global-scale aviation-related air quality impacts, these effects are poised to worsen unless more robust mitigation measures are implemented.

Aircraft operations are typically divided into landing and takeoff (LTO) and non-LTO phases. The majority of emissions are released in the upper troposphere and lower stratosphere, where they spread across intercontinental distances through the formation of secondary pollutants. The resulting impacts on air quality and health are highly variable and influenced by background pollution, weather patterns, fluctuations in air traffic, population density, interactions with other emissions, and climatic factors. This complexity presents considerable challenges for assessing aviation’s true impact.

Numerous studies have evaluated aviation’s impacts on air quality at local, regional, and global levels, but findings vary widely due to differences in atmospheric modeling, chemical processes, and microphysical assumptions. Health impact estimates also differ depending on the pollutant examined, the selected mortality endpoints, and the concentration-response relationships used.

Assessing Global Impacts of Aircraft Emissions on Air Quality and Human Health

The current study quantified the contribution of fixed-wing civil aircraft to ground-level air pollution by comparing atmospheric simulations with and without aviation emissions. It also distinguished the effects of emissions from LTO cycles and estimated the extent to which the full-flight impact could be attributed specifically to NOx by excluding non-NOx aircraft emissions in separate simulations.

Aircraft emissions were represented as monthly-averaged, three-dimensional fields for pollutants including NOx, carbon monoxide (CO), hydrocarbons, and nonvolatile particulate matter. Emissions for 2019 were based on detailed inventories and engine-specific data, while 2040 projections covered “low,” “baseline,” and “high” scenarios to capture uncertainties in traffic growth, fleet turnover, and technological advances. Contributions from business jets and piston aircraft were excluded due to limited data.

The 2040 scenarios incorporated traffic growth, fleet turnover, retirement rates, fuel-efficiency improvements, operational improvements, engine pressure-ratio assumptions, and NOx reduction targets informed by ICAO analyses. The study did not consider potential mitigating effects from expanded biofuel use or aircraft not powered by hydrocarbon fuel, including electric or hydrogen-powered aircraft.

Emissions were calculated by region, aircraft type, and operational factors, and atmospheric impacts were evaluated using the GEOS-Chem model across various meteorological and emissions scenarios. Population exposure and health impacts were estimated globally, with mortality attributed to changes in PM2.5, ozone, and NO2 concentrations across age groups and regions. Uncertainties in these estimates were addressed using established concentration-response functions, confidence intervals, and scenario analyses.

Aviation Emissions Drive Significant Global Health Impacts

In 2019, aircraft full-flight emissions increased ground-level PM2.5 and ozone levels, with PM2.5 impacts greatest in populated regions and ozone effects more spatially widespread. While NO2 levels rose near airports due to low-altitude emissions, they declined in other regions because high-altitude NOx boosted ozone formation, which then lowered NO2 farther from the sources.

Most aviation air quality impacts occurred in the Northern Hemisphere, where most fuel burn and people are concentrated. Aviation's global pollution contribution was modest, but regionally, aircraft accounted for over 2% of PM2.5 in areas of Europe and North America.

Aviation's air quality impacts varied: ozone increased fairly uniformly, while PM2.5 rises were greatest in densely populated areas like Asia, affecting over 1.5 billion people. Although global NO2 generally declined, areas near airports, especially in North America, where LTO emissions are higher, saw significant increases.

In 2019, aviation emissions were estimated to cause 33,900 excess deaths from PM2.5 (95% CI: 23,500 to 45,600), 24,600 from ozone (15,500 to 34,200), and 6,700 from NO2 (4,100 to 9,400), with Asia bearing the largest burden. Non-LTO emissions dominated global PM2.5 and ozone mortality, while LTO emissions were more important near airports and for NO2-related impacts. Widebody and narrowbody aircraft were the main contributors to aviation-related mortality. The choice of concentration-response function also significantly influences these health estimates.

Aircraft emissions are expected to continue affecting air quality, with global changes in PM2.5 and ozone generally following NOx emission trends, though sensitivity decreases in higher-emission scenarios. Depending on socioeconomic conditions, aircraft-attributable mean concentration changes relative to the SSP2-4.5 baseline could fall by 4% or rise by 13% for PM2.5, and decrease by 9% or increase by 3% for ozone. NO2 is projected to keep declining overall, but with regional variation.

Population exposure is expected to rise with increased aircraft NOx emissions, though sensitivity varies by pollutant and scenario. By 2040, excess deaths from aviation emissions could reach 68,000 for PM2.5 (47,100 to 91,900) and 54,100 for ozone (34,100 to 75,100) in the baseline scenario, which is more than double 2019 levels, driven by higher emissions, population growth, and baseline mortality. In the high aircraft-emissions scenario, deaths were projected to rise further, to 83,800 for PM2.5 and 66,300 for ozone. Socioeconomic and non-aviation emission trends may further increase or reduce these health impacts.

Meteorological conditions will also shape future impacts. Using 2040 climate-model meteorology rather than 2019 reanalysis meteorology produced substantially lower aircraft-attributable PM2.5 exposure in some simulations, while ozone exposure was much less affected. Within the 2040 climate-model framework, however, switching non-aviation emissions had a larger effect than switching meteorological scenarios alone. Thus, both emission trends and meteorological assumptions must be considered when estimating health impacts.

Conclusions

Aircraft emissions have a measurable modeled impact on air quality and public health, with the greatest effects seen in densely populated regions and near major airports. As aviation activity and global populations grow, these health risks are projected to rise unless effective mitigation strategies are implemented, particularly measures that reduce aviation NOx emissions while also addressing local particle pollution near airports.

However, the authors note that the absolute mortality estimates depend on the concentration-response functions used, so the precise size of the burden remains uncertain.

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