Influence of weather situation on non-CO<sub>2</sub> aviation climate effects: the REACT4C climate change functions

Abstract

Abstract. Emissions of aviation include CO2, H2O, NOx, sulfur oxides, and soot. Many studies have investigated the annual mean climate impact of aviation emissions. While CO2 has a long atmospheric residence time and is almost uniformly distributed in the atmosphere, non-CO2 gases and particles and their products have short atmospheric residence times and are heterogeneously distributed. The climate impact of non-CO2 aviation emissions is known to vary with different meteorological background situations. The aim of this study is to systematically investigate the influence of characteristic weather situations on aviation climate effects over the North Atlantic region, to identify the most sensitive areas, and to potentially detect systematic weather-related similarities. If aircraft were re-routed to avoid climate-sensitive regions, the overall aviation climate impact might be reduced. Hence, the sensitivity of the atmosphere to local emissions provides a basis for the assessment of weather-related, climate-optimized flight trajectory planning. To determine the climate change contribution of an individual emission as a function of location, time, and weather situation, the radiative impact of local emissions of NOx and H2O to changes in O3, CH4, H2O and contrail cirrus was computed by means of the ECHAM5/MESSy Atmospheric Chemistry model. From this, 4-dimensional climate change functions (CCFs) were derived. Typical weather situations in the North Atlantic region were considered for winter and summer. Weather-related differences in O3, CH4, H2O, and contrail cirrus CCFs were investigated. The following characteristics were identified: enhanced climate impact of contrail cirrus was detected for emissions in areas with large-scale lifting, whereas low climate impact of contrail cirrus was found in the area of the jet stream. Northwards of 60∘ N, contrails usually cause climate warming in winter, independent of the weather situation. NOx emissions cause a high positive climate impact if released in the area of the jet stream or in high-pressure ridges, which induces a south- and downward transport of the emitted species, whereas NOx emissions at, or transported towards, high latitudes cause low or even negative climate impact. Independent of the weather situation, total NOx effects show a minimum at ∼250 hPa, increasing towards higher and lower altitudes, with generally higher positive impact in summer than in winter. H2O emissions induce a high climate impact when released in regions with lower tropopause height, whereas low climate impact occurs for emissions in areas with higher tropopause height. H2O CCFs generally increase with height and are larger in winter than in summer. The CCFs of all individual species can be combined, facilitating the assessment of total climate impact of aircraft trajectories considering CO2 and spatially and temporally varying non-CO2 effects. Furthermore, they allow for the optimization of aircraft trajectories with reduced overall climate impact. This also facilitates a fair evaluation of trade-offs between individual species. In most regions, NOx and contrail cirrus dominate the sensitivity to local aviation emissions. The findings of this study recommend considering weather-related differences for flight trajectory optimization in favour of reducing total climate impact.

Transport Patterns of Global Aviation NO<sub>x</sub> and their Short-term O<sub>3</sub> Radiative Forcing – A Machine Learning Approach

“…America, C2 is the most commonly occurring trajectory type (50%) and also displays the fastest descent at 23.6 hPa•day -1 followed by an increase in altitude. Trajectories C1 -C3 for S. America continue to support the tendency highlighted by Frömming et al (2021) and Rosanka et al (2020), namely that a faster initial descent will yield larger O3 maxima until being washed out after reaching the minimum in altitude. For Eurasia, all trajectories exhibit similar vertical profiles with relatively low rates of descent when compared to C2 in Eurasia during January -March 2014.…”

“…The mixing itself between Lagrangian parcels depends on dimensionless mixing coefficients defined per vertical layer (e.g., the troposphere) and is parameterized via the LGTMIX (LaGrangian Tracer MIXing) sub-model (Brinkop and Jöckel, 2019). Along each of these air parcel trajectory points, the AIRTRAC sub-model then calculates the contribution of the NOx emissions to the atmospheric composition of O3, CH4, HNO3, OH and active nitrogen species (NOy) by also Sander et al, 2011) for the troposphere and stratosphere, as is described by Frömming et al (2021) and Rosanka et al (2020). The effect of a NOx disturbance on the mixing ratios of other chemical species like O3 can be understood in terms of an interaction between production and loss terms in which O3 production is initiated by the reaction 𝑁𝑂 + 𝐻𝑂 2 → 𝑂𝐻 + 𝑁𝑂 2 , followed by the photolysis of NO2 (𝑁𝑂 2 + ℎ𝑣 → 𝑁𝑂 + 𝑂) and finally the combination of oxygen and dioxygen (𝑂 + 𝑂 2 → 𝑂 3 ).…”

“…Short-term NOx effects also induce the second highest ERF across aviation's climate forcers with an estimate of 49.3 mWm -2 [32-76, 90% CI] ( Lee et al, 2021). The climate impact associated with aviation NOx emissions has been studied in terms of varying the cruise flight altitude (Frömming et al, 2012;, emission locations (Stevenson and Derwent 2009;Köhler et al, 2013), seasons (Gilmore et al, 2013;Stevenson et al, 2004), background O3 concentrations (Dahlmann et al, 2011) and weather patterns (Frömming et al, 2021;Rosanka et al, 2020). In regard to research focusing on the spatial relationship between emission location and NOx environmental effects, the work by Stevenson and Derwent (2009) may be referred.…”

“…Gilmore et al (2013) also found larger ozone sensitivities in the Tropics, particularly near the Australasian region. Recent studies by Frömming et al (2021) and Rosanka et al (2020) have adopted a Lagrangian approach to investigate the impact of emitting NOx and H2O in different weather conditions across Summer and Winter in the North Atlantic using the EMAC model. The former investigated trajectories starting at emission regions within and to the west of a high-pressure ridge, analyzing how they contribute differently to O3.…”

Concept of climate-charged airspaces: a potential policy instrument for internalizing aviation's climate impact of non-CO2 effects

“…Lee et al, 2010) and aviation-induced radiative forcing (RF) (as reported by Lee et al, 2009 and adapted by Grewe, Dahlmann, et al, 2017) Emissions of NO x affect the climate indirectly by an increase in ozone concentration (O 3 ; warming effect of 26.3 mW/m 2 ) and a reduction in methane concentration (CH 4 ; cooling effect of −15.4 mW/m 2 ; Grewe et al, 2019), which are both important greenhouse gases. The level of the positive net NO x effect, however, varies greatly with the emission location in terms of altitude (Grewe & Stenke, 2008), geographic region (Köhler et al, 2013;Stevenson & Derwent, 2009), and time of the year (Hoor et al, 2009;Søvde et al, 2014), with the consequence that NO x emissions can even cause a cooling effect in certain regions (Frömming et al, 2021). The largest individual contribution to the total RF of aviation is currently attributed to contrail cirrus (CC), whereas for the induced temperature change the three components CO 2 , NO x , and CC might be about equally important (Grewe, 2020;Ponater & Bickel, 2020).…”