Aircraft Exhaust Plumes Research Articles

The effects of the conversion of nitrogen oxides in aircraft exhaust plumes in global models

A parametrization is needed in global models to account for the sub‐grid chemical processes taking place in the plume of an aircraft, since these processes can cause the conversion of a considerable amount of the emitted NOx to reservoir species, such as HNO3. For this purpose, the chemical conversions of nitrogen oxides in the plume of an aircraft were investigated with a newly developed model. The calculated fractions of different nitrogen compounds formed within 24 hours in the exhaust plumes, differentiated for the global domain and season, were used to modify the original aircraft NOx emissions from the ANCAT emission inventory to emissions of various nitrogen compounds and we applied these to the global Chemistry Transport Model KNMI (CTMK). The results obtained imply that neglect of aircraft plume processes in global modeling leads to an overestimation of the NOx and O3 perturbations. Compared with a CTMK calculation with unmodified aircraft NOx emissions, the NOx perturbations in the North Atlantic flight corridor (NAFC) decreased by 15%–55%, due to conversions in the plumes. The resulting O3 perturbation decreased by 15%–25%.

The role of sulfur emission in volatile particle formation in jet aircraft exhaust plumes

Recent in‐situ emission measurements of the Concorde in the lower stratosphere point to a surprisingly efficient conversion of fuel sulfur to H2SO4 in the exhaust plume. By means of a comprehensive model, the formation and evolution of aerosol particles and precursors are calculated in the diluting aircraft wake. The results provide strong evidence that high levels of SO3 present in the nascent plume are required to explain the observations of large numbers of nanometer‐sized aerosols. Limiting particle formation at emission to keep potential chemical effects on stratospheric ozone small will require control of the sulfur oxidation kinetics during fuel combustion. The similarities between super‐ and subsonic exhaust plumes suggest that the presence of SO3 in the latter will also be a key limiting factor in new aerosol production.

The role of HOx in super‐ and subsonic aircraft exhaust plumes

The generation of sulfuric acid aerosols in aircraft exhaust has emerged as a critical issue in determining the impact of supersonic aircraft on stratospheric ozone. It has long been held that the first step in the mechanism of aerosol formation is the oxidation of SO2 emitted from the engine by OH in the exhaust plume. We report in situ measurements of OH and HO2 in the exhaust plumes of a supersonic (Air France Concorde) and a subsonic (NASA ER‐2) aircraft in the lower stratosphere. These measurements imply that reactions with OH are responsible for oxidizing only a small fraction of SO2 (2%), and thus cannot explain the large number of particles observed in the exhaust wake of the Concorde.

Large‐eddy simulation of aircraft exhaust plumes in the free atmosphere: Effective diffusivities and cross‐sections

The effective diffusion of aircraft emissions in the free stably stratified atmosphere is investigated by means of large‐eddy simulation in a domain of size 4.3 × 1.1 × 1.1 km³. On that scale, the atmosphere is represented by a weakly turbulent flow under uniformly stratified and shearless conditions. It is assumed that aircraft induced turbulence has ceased. The exhaust plumes of aircraft are represented by line sources with Gaussian cross‐sections. The stratification has been varied between 0.006 s−1 and 0.03 s−1. The computed effective horizontal diffusion coefficient lies between 11±2 m²s−1 and 21±4 m²s−1, depending on the level of stratification. Likewise the vertical diffusivity ranges from 2.3±0.6 m²s−1 to 0.37±0.04 m²s−1 in the beginning of the diffusion process, and amounts almost independently of the stratification to about 0.15±0.01 m²s−1 later on. The plume cross‐sections increase with time and stratification. The scattering of the results for a given stratification reflects the action of decaying, anisotropic, and homogeneous turbulence. The results confirm very well data from recent in‐situ flight measurements in the North‐Atlantic flight corridor in the tropopause region.

A trajectory box model for aircraft exhaust plumes

A trajectory box model describing the expansion and cooling of jet aircraft plumes at cruise altitude in the wake regime is presented. The forcing along the trajectory takes into account turbulent entrainment rates for the distinct dynamical regimes (jet, vortex, and dispersion), with special emphasis on the proper treatment of jet mixing. The model is used to study the plume evolution, especially the overall plume dilution history, behind a subsonic B 747 and a planned supersonic airliner under cruising conditions. The accuracy with which microphysically relevant quantities like plume temperature and water saturation ratio can be predicted with the box model is discussed by comparing the results to spatially resolved, two‐dimensional model calculations of jet mixing. As an application, the gas phase chemical conversion of NO into HNO2, of NO2 into HNO3, and of SO2 into H2SO4 taking place in the early jet regime is investigated using a simplified plume chemistry. Maximum conversion rates and their sensitivity to variations of the OH exit plane concentration are examined by means of analytical expressions.

Aerosol formation in aircraft exhaust plumes

Aerosol formation in aircraft exhaust plumes

Nucleation simulations in the wake of a jet aircraft in stratospheric flight

An efficient method for calculating the nucleation rates of H 2SO 4H 2O aerosol droplets is developed using classical nucleation theory for a binary vapor system. The nucleation model is used to predict binary homogeneous and heterogeneous nucleation rates in the exhaust stream of a supersonic aircraft flying in the stratosphere. Calculations indicate that, assuming at least 0.01% of sulfur is emitted as H 2SO 4, the H 2SO 4H 2O particle formation rate is large enough to enhance the background sulfate aerosol concentration substantially. Heterogeneous nucleation, although somewhat slower, may convert a substantial fraction of the soot particles into acid aerosols (notwith-standing rapid water vapor condensation on the soot). Model results are compared with a balloon measurement taken in the aircraft exhaust plume in which the sulfuric acid aerosol concentration was greatly enhanced above the background. The observed aerosols consist of pure sulfuric acid-water solutions without a nucleating “core”, which is consistent with the prompt homogeneous binary sulfuric acid nucleation in the jet plume. Simulations do not support an alternative delayed mechanism that requires photooxidation of SO 2 into H 2SO 4 followed by homogeneous nucleation in the humid air (like the formation of new sulfate aerosols in volcanic eruption clouds).

In situ observations in aircraft exhaust plumes in the lower stratosphere at midlatitudes

Instrumentation on the NASA ER‐2 high‐altitude aircraft has been used to observe engine exhaust from the same aircraft while operating in the lower stratosphere. Encounters with the exhaust plume occurred approximately 10 min after emission with spatial scales near 2 km and durations of up to 10 s. Measurements include total reactive nitrogen, NOy, the component species NO and NO2, CO2, H2O, CO, N2O, condensation nuclei, and meteorological parameters. The integrated amounts of CO2 and H2O during the encounters are consistent with the stoichiometry of fuel combustion (1:1 molar). Emission indices (EI) for NOx (=NO + NO2), CO, and N2O are calculated using simultaneous measurements of CO2. EI values for NOx near 4 g (kg fuel)−1 are in good agreement with values scaled from limited ground‐based tests of the ER‐2 engine. Non‐NOx species comprise less than about 20% of emitted reactive nitrogen, consistent with model evaluations. In addition to demonstrating the feasibility of aircraft plume detection, these results increase confidence in the projection of emissions from current and proposed supersonic aircraft fleets and hence in the assessment of potential long‐term changes in the atmosphere.

Impact of aircraft emissions on stratospheric ozone: A research strategy

We briefly summarize what is currently known about the impact of aircraft emissions on the chemical composition of the upper troposphere and lower stratosphere, with special emphasis on the ozone balance. We report on recent research work concerning the chemical transformation and particle formation processes in young aircraft exhaust plumes and outline a possible research strategy to investigate the present and future impact of air traffic on the stratospheric ozone layer by means of process-related numerical modeling and experimental near-field studies.

An analysis of aircraft exhaust plumes from accidental encounters

An analysis of data obtained during the second Airborne Arctic Stratospheric Expedition (AASE‐II) was made with emphasis on aircraft exhaust plumes accidentally encountered during the mission. Twenty spikes were found with peak NOy increments ≥1 ppbv. The examination of CO and CO2 indicates that there was only one NOy spike having clearly corresponding spikes of both CO and CO2, and another four with unambiguous CO2 spikes. No significant increases were found for CH4 and N2O for these 5 spikes. The ratio of the excess CO2 and NOy compares well with the ratio of published subsonic aircraft emission indices. The study of the selected spikes from the DC‐8 and another two spikes observed during other missions shows that the odd nitrogen other than NOx accounts for a very small percentage of the NOy increase associated with the observed spikes.

Evolution of the concentrations of trace species in an aircraft plume: Trajectory study

Permanent increase of the subsonic aviation flights and attempts to develop high‐speed civil transport (HSCT) necessitate an assessment of their possible environmental impacts. To evaluate global aviation effects, it is important to know the role of the chemical transformations inside an aircraft plume taking into account heterogeneous reactions. The goal of this work is to model the principal physical and chemical processes occurring inside an aircraft exhaust plume. A new box model which calculates 41 relevant Ox, HOx, NOx, ClOx, BrOx, SOx, and HC species and includes the possible heterogeneous reactions on the combustion aerosol and ice contrail particles is proposed. The simplified descriptions of the aircraft plume dilution and ice contrail formation are described. The transformations inside the aircraft wake are presented for the trajectories of the exhaust product motions at the levels of 200 and 100 mbar calculated for the particular atmospheric conditions on April 25, 1986. The following problems are discussed: the ozone response at these altitudes, the oxidation rate of NOx and SO2, the role of the heterogeneous reactions on the combustion aerosol and contrail particles, and the possibility of ice and nitric acid trihydrate (NAT or HNO2•3H2O) particle formation inside the wake. The model results are in agreement with available experimental data for NO, NO2, HNO3, HNO2, and SO2. Analytical expressions are proposed to evaluate the oxidation rates of NOx, and SO2 in the aircraft wake. The local ozone response is small (between 0.6% at 200 mb and −0.1% at 100 mb). Possible future investigations are proposed.

Dynamics of aircraft exhaust plumes in the jet-regime

Abstract. A computational model describing the two-dimensional, turbulent mixing of a single jet of exhaust gas from aircraft engines with the ambient atmosphere is presented. The underlying assumptions and governing equations are examined and supplemented by a discussion of analytical solutions. As an application, the jet dynamics of a B747-400 aircraft engine in cruise and its dependence on key parameters is investigated in detail. The computer code for this dynamical model is computationally fast and can easily be coupled to complex chemical and microphysical models in order to perform comprehensive studies of atmospheric effects from aircraft exhaust emissions in the jet regime.

Dynamics of aircraft exhaust plumes in the jet-regime

Dynamics of aircraft exhaust plumes in the jet-regime

The dynamics and radiant intensity of large hydrogen flames

Measurements of the spectral radiant intensity and structure of large turbulent hydrogen diffusion flames, with mass flow rates from 5.4 to 68kg/sec, are presented. These measurements are compared with predictions of the reacting, buoyant flowfield and radiant intensities, utilizing the flowfield and infrared radiation computer codes originally developed to determine rocket and jet aircraft exhaust plume characteristics. The predictions of radiant intensity are shown to be within the data fluctuations (±25%) and the predicted length of the diffusion flame is consistent with the data. However, the predicted flame width is somewhat smaller than that obtained from thermovision measurements of the flame (1.9–3.3 microns). This is attributed to the failure of the turbulence model used in the flowfield code to accurately treat the large density gradients across the flame. It is shown that, for the conditions of these tests, the radiant intensity does not scale linearly with mass flow rate. The ratio of radiant intensity to rate of heat release, F, is demonstrated to vary from 0.153 at very low velocities (small Froude numbers) to 0.086 at the high velocities (large Froude numbers). This trend of decreasing F with increasing velocity is consistent with the experimental observations of Brzustowski et al. 1 The reasonable agreement between the theoretical predictions and data suggests that these codes, and selected laboratory experiments, may be used to develop scaling relations for radiant intensity and flame structure which include effects of optical depth, mass flow rate, velocity, pipe radius, and Froude number.