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Aviation produces a net climate warming contribution that comprises multiple forcing terms of mixed sign. Aircraft NOx emissions are associated with both warming and cooling terms, with the short-term increase in O3 induced by NOx emissions being the dominant warming effect. The uncertainty associated with the magnitude of this climate forcer is amongst the highest out of all contributors from aviation and is owed to the nonlinearity of the NOx–O3 chemistry and the large dependency of the response on space and time, i.e., on the meteorological condition and background atmospheric composition. This study addresses how transport patterns of emitted NOx and their climate effects vary with respect to regions (North America, South America, Africa, Eurasia and Australasia) and seasons (January–March and July–September in 2014) by employing global-scale simulations. We quantify the climate effects from NOx emissions released at a representative aircraft cruise altitude of 250 hPa (∼10 400 m) in terms of radiative forcing resulting from their induced short-term contributions to O3. The emitted NOx is transported with Lagrangian air parcels within the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model. To identify the main global transport patterns and associated climate impacts of the 14 000 simulated air parcel trajectories, the unsupervised QuickBundles clustering algorithm is adapted and applied. Results reveal a strong seasonal dependence of the contribution of NOx emissions to O3. For most regions, an inverse relationship is found between an air parcel's downward transport and its mean contribution to O3. NOx emitted in the northern regions (North America and Eurasia) experience the longest residence times in the upper midlatitudes (40 %–45 % of their lifetime), while those beginning in the south (South America, Africa and Australasia) remain mostly in the Tropics (45 %–50 % of their lifetime). Due to elevated O3 sensitivities, emissions in Australasia induce the highest overall radiative forcing, attaining values that are larger by factors of 2.7 and 1.2 relative to Eurasia during January and July, respectively. The location of the emissions does not necessarily correspond to the region that will be most affected – for instance, NOx over North America in July will induce the largest radiative forcing in Europe. Overall, this study highlights the spatially and temporally heterogeneous nature of the NOx–O3 chemistry from a global perspective, which needs to be accounted for in efforts to minimize aviation's climate impact, given the sector's resilient growth.

Aviation produces a net climate warming contribution that comprises multiple forcing terms of mixed sign. Aircraft NOx emissions are associated with both warming and cooling terms, with the short-term increase in O3 induced by NOx emissions being the dominant warming effect. The uncertainty associated with the magnitude of this climate forcer is amongst the highest out of all contributors from aviation and is owed to the non-linearity of the NOx–O3 chemistry and the large dependency of the response on space and time, i.e., on the meteorological condition and background atmospheric composition. This study addresses how transport patterns of emitted NOx and their climate effects vary with respect to regions (North America, South America, Africa, Eurasia and Australasia) and seasons (January–March and July–September in 2014) by employing global-scale simulations. We quantify the climate effects from NOx emissions released at 250 hPa (~ 10 400 m) in terms of radiative forcing resulting from their induced short-term contributions to O3. The emitted NOx is transported with Lagrangian air parcels within the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model. To identify the main global transport patterns and associated climate impacts of the 14 000 simulated air parcel trajectories, the unsupervised QuickBundles clustering approach is adapted and applied. Results reveal a strong seasonal dependence of the contribution of NOx emissions to O3. For most regions, a negative correlation is found between an air parcel’s downward transport and its mean contribution to O3. NOx emitted in the Northern regions (North America and Eurasia) experiences the longest residence times in upper midlatitudes (40–45 % of their lifetime), while those beginning in the South (South America, Africa and Australasia) remain mostly in the Tropics (45–50 % of their lifetime). Due to elevated O3 sensitivities, emissions in Australasia induce the highest overall radiative forcing, attaining values that are larger by factors of 2.7 and 1.2 relative to Eurasia during January and July, respectively. The location of the emissions does not necessarily correspond to the region that will be most affected – for instance, NOx over North America in July will induce the largest radiative forcing in Europe. Overall, this study highlights the spatially and temporally heterogeneous nature of the NOx–O3 chemistry from a global perspective, which needs to be accounted for in efforts to minimize aviation’s climate impact, given the sector’s resilient growth.

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.

Outdoor air pollution adversely affects human health and is estimated to be responsible for five to ten per cent of the total annual premature mortality in the contiguous United States1–3. Combustion emissions from a variety of sources, such as power generation or road traffic, make a large contribution to harmful air pollutants such as ozone and fine particulate matter (PM2.5)4. Efforts to mitigate air pollution have focused mainly on the relationship between local emission sources and local air quality2. Air quality can also be affected by distant emission sources, however, including emissions from neighbouring federal states5,6. This cross-state exchange of pollution poses additional regulatory challenges. Here we quantify the exchange of air pollution among the contiguous United States, and assess its impact on premature mortality that is linked to increased human exposure to PM2.5 and ozone from seven emission sectors for 2005 to 2018. On average, we find that 41 to 53 per cent of air-quality-related premature mortality resulting from a state’s emissions occurs outside that state. We also find variations in the cross-state contributions of different emission sectors and chemical species to premature mortality, and changes in these variations over time. Emissions from electric power generation have the greatest cross-state impacts as a fraction of their total impacts, whereas commercial/residential emissions have the smallest. However, reductions in emissions from electric power generation since 2005 have meant that, by 2018, cross-state premature mortality associated with the commercial/residential sector was twice that associated with power generation. In terms of the chemical species emitted, nitrogen oxides and sulfur dioxide emissions caused the most cross-state premature deaths in 2005, but by 2018 primary PM2.5 emissions led to cross-state premature deaths equal to three times those associated with sulfur dioxide emissions. These reported shifts in emission sectors and emission species that contribute to premature mortality may help to guide improvements to air quality in the contiguous United States. This analysis of the exchange of air pollution amongst the contiguous United States finds that, on average, around half of the early deaths caused by a state’s air pollution occurs outside that state, with different contributions by different emission sectors and chemical species.

Land cover plays an important role in the Earth's climate as it affects multiple biochemical cycles and is critical for food security and biodiversity. As land cover is continuously evolving, influenced by anthropogenic and other factors, the availability of temporally varying land cover data sets of large spatial domains is integral to understanding, monitoring, and informing environmental management efforts. Here we use classification trees to generate annual land cover maps of the European continent for 2001 to 2019 on a ∼250 m resolution. The classification trees are trained using gap-filled and smoothed MODIS normalised difference vegetation index (NDVI) satellite data, as well as CORINE reference land cover data. We apply the bagging ensemble technique on oversampled NDVI data, with an additional majority vote for overlapping segments over the continent-wide domain. We distinguish between 39 land cover classes, with a total classification accuracy of 75% and average precision of 76%. The accuracy varies between the classes, with common classes (e.g. agricultural and forest classes) performing better than rarer ones (e.g. artificial land cover). Over the entire continent, we find that artificial land cover, wetlands, and forests have increased on average by 0.76, 0.50 and 0.22%/year respectively, while the agricultural area has decreased by 0.21%/year. We also quantify these changes in land cover on a national and metropolitan level. Given the near-real-time availability of global NDVI data, we note the potential of the presented approach for generating ‘near-real-year’ annual land cover data sets of large geographic domains, for the continuous monitoring of land cover change and the effects of interventions.

© 2020, The Author(s), under exclusive licence to Springer Nature America, Inc. Expanded use of reduced complexity approaches in epidemiology and environmental justice investigations motivates detailed evaluation of these modeling approaches. Chemical transport models (CTMs) remain the most complete representation of atmospheric processes but are limited in applications that require large numbers of runs, such as those that evaluate individual impacts from large numbers of sources. This limitation motivates comparisons between modern CTM-derived techniques and intentionally simpler alternatives. We model population-weighted PM2.5 source impacts from each of greater than 1100 coal power plants operating in the United States in 2006 and 2011 using three approaches: (1) adjoint PM2.5 sensitivities calculated by the GEOS-Chem CTM; (2) a wind field-based Lagrangian model called HyADS; and (3) a simple calculation based on emissions and inverse source-receptor distance. Annual individual power plants’ nationwide population-weighted PM2.5 source impacts calculated by HyADS and the inverse distance approach have normalized mean errors between 20 and 28% and root mean square error ranges between 0.0003 and 0.0005 µg m−3 compared with adjoint sensitivities. Reduced complexity approaches are most similar to the GEOS-Chem adjoint sensitivities nearby and downwind of sources, with degrading performance farther from and upwind of sources particularly when wind fields are not accounted for.

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.

Fossil fuel combustion releases carbon dioxide into the atmosphere along with co-pollutants such as sulfur dioxide, nitrogen oxides, and others. These emissions result in environmental externalities primarily in terms of climate and air quality. Here we quantify the cost of co-pollutant emissions per ton of CO2 emissions from US electric power generation. We measure the co-pollutant cost of carbon (CPCC) as the total value of statistical life associated with US-based premature mortalities attributable to co-pollutant emissions, per mass of CO2. We find an average CPCC of ∼$45 per metric ton (mt) of CO2 for the year 2011 (in 2017 USD). This is ∼20% higher than the central Social Cost of Carbon (SCC) measure of climate damages that was used by the Obama administration in its regulatory impact analysis for the Clean Power Plan (CPP), and >8 times higher than the SCC used by the Trump administration in its analysis for the Plan’s repeal. At the state-level, the CPCC ranged from ∼$7/mt CO2 for Arizona to ∼$96/mt CO2 for New Jersey. We calculate the CPCC trends from 2002 to 2017 and find a 71% decrease at the national level, contributing to total savings of ∼$1 trillion in averted mortality from power plant emissions over this period. By decomposing the aggregate and fuel-specific co-pollutant intensities into simultaneous (CO2-driven) and autonomous components, we conclude that the CPCC trends originated mainly from targeted efforts to reduce co-pollutant emissions, e.g. through fuel switching (from coal to natural gas) and autonomous changes in co-pollutant emissions. The results suggest that the overall benefit to society from policies to curtail carbon emissions may be enhanced by focusing on pollution sources where the associated air-quality co-benefits are greatest. At the same time, continued efforts to reduce co-pollutant intensities, if technologically feasible, could help to mitigate the air-quality damages of the CPP’s repeal and replacement.

Aviation emissions lead to degraded air quality and adverse human health impacts, making air quality one of the leading environmental externalities associated with aviation. Aviation emissions have been growing steadily over the past decades, and, despite the current hindrance in air traffic due to the COVID- 19 pandemic, they are forecasted to continue to grow in the long-term. As a result, mitigating aviation’s adverse air quality impacts is an increasingly pressing challenge for the aviation industry. At the same time, the aviation industry has inherently long timelines, indicating that sustainability-related regulatory and technological decisions made presently will take effect over the next 30+ years. Over such timelines, the changing atmospheric composition, driven by meteorological and background (non-aviation) emissions changes, results in a changing atmospheric response to emissions. This work summarizes recent advancements on this and discusses their implications for the aviation sector. First, aviation emissions and the resulting air quality impacts are described. The role of the atmospheric sensitivities to emissions and their evolution over time is then discussed. Finally, the implications for the long timelines associated with aviation mitigation options are underlined. Current challenges as well as opportunities for future research to resolve current assessment shortcomings are also presented.

Outdoor air pollution adversely affects human health and is estimated to be responsible for five to ten per cent of the total annual premature mortality in the contiguous United States

In September 2015, the Volkswagen Group (VW) admitted the use of 'defeat devices' designed to lower emissions measured during VW vehicle testing for regulatory purposes. Globally, 11 million cars sold between 2008 and 2015 are affected, including about 2.6 million in Germany. On-road emissions tests have yielded mean on-road NO[subscript x] emissions for these cars of 0.85 g km[superscript −1], over four times the applicable European limit of 0.18 g km[superscript −1]. This study estimates the human health impacts and costs associated with excess emissions from VW cars driven in Germany. A distribution of on-road emissions factors is derived from existing measurements and combined with sales data and a vehicle fleet model to estimate total excess NO[subscript x] emissions. These emissions are distributed on a 25 by 28 km grid covering Europe, using the German Federal Environmental Protection Agency's (UBA) estimate of the spatial distribution of NO[subscript x] emissions from passenger cars in Germany. We use the GEOS-Chem chemistry-transport model to predict the corresponding increase in population exposure to fine particulate matter and ozone in the European Union, Switzerland, and Norway, and a set of concentration-response functions to estimate mortality outcomes in terms of early deaths and of life-years lost. Integrated over the sales period (2008–2015), we estimate median mortality impacts from VW excess emissions in Germany to be 1200 premature deaths in Europe, corresponding to 13 000 life-years lost and 1.9 billion EUR in costs associated with life-years lost. Approximately 60% of mortality costs occur outside Germany. For the current fleet, we estimate that if on-road emissions for all affected VW vehicles in Germany are reduced to the applicable European emission standard by the end of 2017, this would avert 29 000 life-years lost and 4.1 billion 2015 EUR in health costs (median estimates) relative to a counterfactual case with no recall., Germany. Umweltbundesamt (UBA)

Aircraft movements on the airport surface are responsible for CO 2 emissions that contribute to climate change and other emissions that affect air quality and human health. While the potential for optimizing aircraft surface movements to minimize CO 2 emissions has been assessed, the implications of CO 2 emissions minimization for air quality have not been quantified. In this paper, we identify conditions in which there is a tradeoff between CO 2 emissions and population exposure to O 3 and secondary PM 2.5 – i.e. where decreasing fuel burn (which is directly proportional to CO 2 emissions) results in increased exposure. Fuel burn and emissions are estimated as a function of thrust setting for five common gas turbine engines at 34 US airports. Regional air quality impacts, which are dominated by ozone and secondary PM 2.5 , are computed as a function of airport location and time using the adjoint of the GEOS-Chem chemistry-transport model. Tradeoffs between CO 2 emissions and population exposure to PM 2.5 and O 3 occur between 2–18% and 5–60% of the year, respectively, depending on airport location, engine type, and thrust setting. The total duration of tradeoff conditions is 5–12 times longer at maximum thrust operations (typical for takeoff) relative to 4% thrust operations (typical for taxiing). Per kilogram of additional fuel burn at constant thrust setting during tradeoff conditions, reductions in population exposure to PM 2.5 and O 3 are 6–13% and 32–1060% of the annual average (positive) population exposure per kilogram fuel burn, where the ranges encompass the medians over the 34 airports. For fuel burn increases due to thrust increases (i.e. for constant operating time), reductions in both PM 2.5 and O 3 exposure are 1.5–6.4 times larger in magnitude than those due to increasing fuel burn at constant thrust (i.e. increasing operating time). Airports with relatively high population exposure reduction potentials – which occur due to a combination of high duration and magnitude of tradeoff conditions – are identified. Our results are the first to quantify the extent of the tradeoff between CO 2 emissions and air quality impacts at airports. This raises the possibility of reducing the air quality impacts of airports beyond minimizing fuel burn and/or optimizing for minimum net environmental impact.

Aviation emissions have been found to cause 5% of global anthropogenic radiative forcing and ∼16 000 premature deaths annually due to impaired air quality. When aiming to reduce these impacts, decision makers often face trade-offs between different emission species or impacts in different times and locations. To inform rational decision-making, this study computes aviation’s marginal climate and air quality impacts per tonne of species emitted and accounts for the altitude, location, and chemical composition of emissions. Climate impacts are calculated using a reduced-order climate model, and air quality-related health impacts are quantified using marginal atmospheric sensitivities to emissions from the adjoint of the global chemistry-transport model GEOS-Chem in combination with concentration response functions and the value of statistical life. The results indicate that 90% of the global impacts per unit of fuel burn are attributable to cruise emissions, and that 64% of all damages are the result of air quality impacts. Furthermore, nitrogen oxides (NO x ), carbon dioxide (CO2), and contrails are collectively responsible for 97% of the total impact. Applying our result metrics to an example, we find that a 20% NOx stringency scenario for new aircraft would reduce the net atmospheric impacts by 700 m USD during the first year of operation, even if the NO x emission reductions cause a small increase in CO2 emissions of 2%. In such a way, the damage metrics can be used to rapidly evaluate the atmospheric impacts of market growth as well as emissions trade-offs of aviation-related policies or technology improvements.

Investigation of the landing gear noise of the Boeing 747-400 in flight. Comparison of different fly-over velocities in order to obtain a scaling law for the Sound pressure Level based on microphone Array measurements.

The US Environmental Protection Agency (EPA) has alleged that Volkswagen Group of America (VW) violated the Clean Air Act (CAA) by developing and installing emissions control system 'defeat devices' (software) in model year 2009–2015 vehicles with 2.0 litre diesel engines. VW has admitted the inclusion of defeat devices. On-road emissions testing suggests that in-use NO[subscript x] emissions for these vehicles are a factor of 10 to 40 above the EPA standard. In this paper we quantify the human health impacts and associated costs of the excess emissions. We propagate uncertainties throughout the analysis. A distribution function for excess emissions is estimated based on available in-use NO[subscript x] emissions measurements. We then use vehicle sales data and the STEP vehicle fleet model to estimate vehicle distance traveled per year for the fleet. The excess NO[subscript x] emissions are allocated on a 50 km grid using an EPA estimate of the light duty diesel vehicle NO[subscript x] emissions distribution. We apply a GEOS-Chem adjoint-based rapid air pollution exposure model to produce estimates of particulate matter and ozone exposure due to the spatially resolved excess NO[subscript x] emissions. A set of concentration-response functions is applied to estimate mortality and morbidity outcomes. Integrated over the sales period (2008–2015) we estimate that the excess emissions will cause 59 (95% CI: 10 to 150) early deaths in the US. When monetizing premature mortality using EPA-recommended data, we find a social cost of ~$450m over the sales period. For the current fleet, we estimate that a return to compliance for all affected vehicles by the end of 2016 will avert ~130 early deaths and avoid ~$840m in social costs compared to a counterfactual case without recall.