The impact of weather patterns and related transport processes on aviation's contribution to ozone and methane concentrations from NO<sub><i>x</i></sub> emissions

Abstract

Abstract. Aviation-attributed climate impact depends on a combination of composition changes in trace gases due to emissions of carbon dioxide (CO2) and non-CO2 species. Nitrogen oxides (NOx = NO + NO2) emissions induce an increase in ozone (O3) and a depletion of methane (CH4), leading to a climate warming and a cooling, respectively. In contrast to CO2, non-CO2 contributions to the atmospheric composition are short lived and are thus characterised by a high spatial and temporal variability. In this study, we investigate the influence of weather patterns and their related transport processes on composition changes caused by aviation-attributed NOx emissions. This is achieved by using the atmospheric chemistry model EMAC (ECHAM/MESSy). Representative weather situations were simulated in which unit NOx emissions are initialised in specific air parcels at typical flight altitudes over the North Atlantic flight sector. By explicitly calculating contributions to the O3 and CH4 concentrations induced by these emissions, interactions between trace gas composition changes and weather conditions along the trajectory of each air parcel are investigated. Previous studies showed a clear correlation between the prevailing weather situation at the time when the NOx emission occurs and the climate impact of the NOx emission. Here, we show that the aviation NOx contribution to ozone is characterised by the time and magnitude of its maximum and demonstrate that a high O3 maximum is only possible if the maximum occurs early after the emission. Early maxima occur only if the air parcel, in which the NOx emission occurred, is transported to lower altitudes, where the chemical activity is high. This downward transport is caused by subsidence in high-pressure systems. A high ozone magnitude only occurs if the air parcel is transported downward into a region in which the ozone production is efficient. This efficiency is limited by atmospheric NOx and HOx concentrations during summer and winter, respectively. We show that a large CH4 depletion is only possible if a strong formation of O3 occurs due to the NOx emission and if high atmospheric H2O concentrations are present along the air parcel's trajectory. Only air parcels, which are transported into tropical areas due to high-pressure systems, experience high concentrations of H2O and thus a large CH4 depletion. Avoiding climate-sensitive areas by rerouting aircraft flight tracks is currently computationally not feasible due to the long chemical simulations needed. The findings of this study form a basis of a better understanding of NOx climate-sensitive areas and through this will allow us to propose an alternative approach to estimate aviation's climate impact on a day-to-day basis, based on computationally cheaper meteorological simulations without computationally expensive chemistry. This comprises a step towards a climate impact assessment of individual flights, here with the contribution of aviation NOx emissions to climate change, ultimately enabling routings with a lower climate impact by avoiding climate-sensitive regions.

The impact of organic pollutants from Indonesian peatland fires on the tropospheric and lower stratospheric composition

“…SCAV calculates the transfer of species into and out of rain and cloud droplets using the Henry's law equilibrium, acid dissociation equilibria, oxidation-reduction reactions, heterogeneous reactions on droplet surfaces, and aqueous-phase photolysis reactions (Tost et al, 2006). As mentioned earlier and as demonstrated by Rosanka et al (2021a), in-cloud OVOC oxidation significantly influences the atmospheric composition. However, the ordinary differential equations (ODE) systems resulting from the combination of gas-phase and in-cloud aqueous-phase suffer from (1) a higher stiffness due to fast acid-base equilibria and phase-transfer reactions and (2) load imbalance on high-performance computing (HPC) systems due to the sparsity of clouds.…”

“…The degradation of methane (CH 4 ) and non-methane hydrocarbons (NMHC) in the atmosphere accounts for almost half of the global CO sources (Zheng et al, 2019). In the atmosphere, CO mainly reacts with OH, and the EMAC estimates by Lelieveld et al (2016) and more recently by Rosanka et al (2021a) show that CO largely determines the atmospheric oxidation capacity. To a lesser extent, CO is deposited (Stein et al, 2014).…”

“…Many oxygenated VOCs (OVOCs) have a high solubility and quickly partition and react in cloud droplets influencing radical concentrations and the atmospheric composition in general (Herrmann et al, 2015). Rosanka et al (2021a) showed that the in-cloud OVOC oxidation has a significant impact on the predicted concentrations of VOCs, key oxidants, and O 3 . In the past, global atmospheric chemistry models were not capable of representing this process explicitly or in its full complexity (Ervens, 2015).…”

“…In the past, global atmospheric chemistry models were not capable of representing this process explicitly or in its full complexity (Ervens, 2015). However, the recently developed Jülich Aqueous-phase Mechanism of Organic Chemistry (JAMOC, Rosanka et al, 2021a, b) comprises an advanced in-cloud OVOC oxidation scheme suitable to be used in the ECHAM/MESSy Atmospheric Chemistry (EMAC, Jöckel et al, 2010) model. This allows us to assess the importance of this in-cloud oxidation process during the VOCdominated Indonesian peatland fires.…”

Organic pollutants from tropical peatland fires: regional influences and its impact on lower stratospheric ozone

“…Here, aviation NO x emissions lead to a formation of O 3 and a depletion of methane (CH 4 ). Recently, Rosanka et al (2020a) showed that the enhancement in O 3 is limited by the background concentrations of NO x and HO x . If enough HO x is available, a lower background NO x concentration results in a higher O 3 gain.…”