P. Schulte

In Situ Observations of Air Traffic Emission Signatures in the North Atlantic Flight Corridor

Focussed aircraft measurements have been carried out over the eastern North Atlantic to search for signals of air traffic emissions in the flight corridor region. Observations include NO, NO2, HNO3, SO2, O3, H2O, total condensation nuclei (CN), and meteorological parameters. A flight pattern with constant-altitude north-south legs across the major North Atlantic air traffic tracks was flown. Signatures of air traffic emissions were clearly detected for NOx, SO2, and CN with peak concentrations of 2 ppbv, 0.25 ppbv, and 500 cm−3, respectively, exceeding background values by factors of 30 (NOx), 5 (SO2), and 3 (CN). The observed NOx, SO2, and CN peaks were attributed to aircraft plumes based on radar observations of the source air traffic and wind measurements. Major aircraft exhaust signatures are due to relatively fresh emissions, i.e., superpositions of 2 to 5 plumes with ages of about 15 min to 3 hs. The observed plume peak concentrations of NOx compare fairly well with concentrations computed with a Gaussian plume model using horizontal and vertical diffusivities as obtained by recent large-eddy simulations, measured vertical wind shear, and the corridor air traffic information. For the major emission signatures a mean CN/NOx abundance ratio of 300 cm−3ppbv−1 was measured corresponding to an emission index (EI) of about 1016 particles per 1 kg fuel burnt. This is higher than the expected soot particle EI of modern wide-bodied aircraft. For the most prominent plumes no increase of HNO3 concentrations exceeding variations of background values was observed. This indicates that only a small fraction of the emitted NOx is oxidized in the plumes within a timescale of about 3 hs for the conditions of the measurements.

Estimate of diffusion parameters of aircraft exhaust plumes near the tropopause from nitric oxide and turbulence measurements

Horizontal and vertical plume scales and respective diffusivities for dispersion of exhaust plumes from airliners at cruising altitudes are determined from nitric oxide (NO) and turbulence data measured with the DLR Falcon research aircraft flying through the plumes. Ten plumes of known source aircraft were encountered about 5 to 100 min after emission at about 9.4 to 11.3 km altitude near the tropopause in the North Atlantic flight corridor at 8°W on three days in October 1993. The ambient atmosphere was stably stratified with bulk Richardson numbers greater than 10. The measured NO peaks had half widths of 500 to 2000 m with maximum concentrations up to 2.4 parts per billion by volume (ppbv), clearly exceeding the background values between 0.13 and 0.5 ppbv. For analysis the measured plumes are approximated by an analytical Gaussian plume model which accounts for anisotropic diffusion in the stably stratified atmosphere and for shear. Two methods are given to obtain diffusivity parameters from either the individual plume data or the set of all plume measurements. Using estimates of the emitted mass of NO per unit length, the vertical plume width is found to be 140 m on average. This width is related to mixing in the initial trailing vortex pair of the aircraft. The range of the plume data suggests vertical diffusivity values between 0 and 0.6 m2 s−1. The turbulence data exhibit strong anisotropic air motions with practically zero turbulent dissipation and weak vertical velocity fluctuations. This implies very small vertical diffusivities. The horizontal diffusivity is estimated as between 5 and 20 m2 s−1 from the increase of horizontal plume scales with time. For constant diffusivities, shear dominates the lateral dispersion after a time of about 1 hour even for the cases with only a weak mean shear of 0.002 s−1.

Observation of upper tropospheric sulfur dioxide- and acetone-pollution: Potential implications for hydroxyl radicaland aerosol formation

Aircraft-based measurements of sulfur dioxide, acetone, carbon dioxide, and condensation nuclei (CN) were made over the north-eastern Atlantic at upper tropospheric altitudes, around 9000 m. On October 14, 1993, strong SO2- and acetone-pollution (both up to 3 ppbv) were observed, which were accompanied by a CO2-enhancement of up to 6 ppmv, and large CN-concentrations of up to about 1500 cm−3 (for radii ≥ 6 nm). CN, excess CO2, and to a lesser degree also acetone, were positively correlated with SO2. Air mass trajectory analyses indicate, that most of the air masses encountered by our aircraft originated from the polluted planetary boundary layer of the North-Eastern U. S. approximately 4–5 days prior to our measurements, and that polluted boundary layer air experienced fast vertical transport to the upper troposphere as well as horizontal transport across the Atlantic. From our data we conclude, that in the polluted air mass around 9000 m altitude HOx-formation, photochemical SO2-conversion to gaseous H2SO4, and eventually also CN-formation by homogeneous bimolecular (H2SO4-H2O) nucleation may have taken place with enhanced efficiency.

NO x emission indices of subsonic long‐range jet aircraft at cruise altitude: In situ measurements and predictions

In the course of the Commissions of the European Communities project “Pollution From Aircraft Emissions in the North Atlantic Flight Corridor (POLINAT)”, in situ measurements of NO, NOx , and CO2 volume mixing ratios in the near-field exhaust plumes of seven subsonic long-range jet aircraft have been carried out by using the research aircraft Falcon of the Deutsche Forschungsanstalt fur Luft- und Raumfahrt (DLR). For three additional aircraft, only NO and CO2 were measured. Plume ages of 50 s to 150 s have been covered, with maximum observed exhaust gas enhancements of 319 parts per billion by volume and 51 parts per million by volume for Δ[NOx] and Δ[CO2], respectively, in relation to ambient values. Aircraft cruising altitudes and Mach numbers ranged from 9.1 to 11.3 km and from 0.77 to 0.85, respectively. These measurements are used to derive NOx emission indices for seven of the individual aircraft/engine combinations. The NOx emission indices derived range from 12.3 g/kg to 30.4 g/kg. They are compared with predicted emission index values, calculated for the same aircraft engine and the actual conditions by using two newly developed fuel flow correlation methods. The calculated emission indices were mostly within or close to the error limits of the measured values. On average, the predictions from both methods were 12% lower than the measured values, with an observed maximum deviation of 25%. The ratio γ = [NO2]/[NOx] found during the present measurements ranged from 0.06 to 0.11 for five daytime cases and was around 0.22 for two nighttime cases. By use of a simple box model of the plume chemistry and dilution these data were used to estimate the initial value γ0 present at the engine exit plane. We found γ0 values between 0 and 0.15. These were applied to estimate the corresponding NO2 for the three cases in which only NO was measured.

Distributions of NO, NO x , and NO y in the upper troposphere and lower stratosphere between 28° and 61°N during POLINAT 2

During the Pollution From Aircraft Emissions in the North Atlantic Flight Corridor 2 (POLINAT 2) field campaign the distribution of NO, NOx , and NOy in the upper troposphere and lowermost stratosphere over the eastern North Atlantic was measured using the Deutsches Zentrum fur Luft- und Raumfahrt research aircraft Falcon. Based from Shannon Airport in Ireland, 14 flights were carried out between September 19 and October 25, 1997. The measurements were performed in and out of the North Atlantic flight corridor covering latitudes between 28°N and 61°N. A marked latitudinal gradient in NO, NOx , and NOy , the sum of all reactive nitrogen compounds, was observed. Mean NO volume mixing ratios in the upper troposphere increased from about 50 parts per trillion by volume (pptv) at 28°N to about 180 pptv at 59°N. A similar latitude dependence was also found for NO x and NO y . In the northern part of the POLINAT 2 measuring area, NO and NO x volume mixing ratios increased significantly with increasing altitude withmaximum values around the tropopause, while in the southern part of the measuring area no strong altitude gradient was observed. NO and NOx did not show a substantial gradient across the tropopause. NO/NOy and NOy /O3 ratios showed maximum values of about 0.30 ppbv/ppbv and 0.012 ppbv/ppbv, respectively, around the tropopause. The POLINAT 2 observations suggest that aircraft emissions are an important source of NOx and NOy in the region studied. Also, the present measurements contribute to the data set obtained in the North Atlantic flight corridor during the last few years and help to establish a NOx climatology around the tropopause for this region.

First direct sulfuric acid detection in the exhaust plume of a jet aircraft in flight

Sulfuric acid (SA) was for the first time directly detected in the exhaust plume of a jet aircraft in flight. The measurements were made by a novel aircraft-based VACA (Volatile Aerosol Component Analyzer) instrument of MPI-K Heidelberg while the research aircraft Falcon was chasing another research aircraft ATTAS. The VACA measures the total SA in the gas and in volatile submicron aerosol particles. During the chase the engines of the ATTAS alternatively burned sulfur-poor and sulfur-rich fuel. In the sulfur-rich plume very marked enhancements of total SA were observed of up to 1300 pptv which were closely correlated with ΔCO2 and ΔT and were far above the local ambient atmospheric background-level of typically 15-50 pptv. Our observations indicate a lower limit for the efficiency ɛ for fuel-sulfur conversion to SA of 0.34 %.

Model calculations of the impact of NO x from air traffic, lightning, and surface emissions, compared with measurements

The impact of NOx from aircraft emissions, lightning, and surface contributions on atmospheric nitrogen oxides and ozone in the North Atlantic flight corridor has been investigated with the three-dimensional global chemistry transport model TM3 by partitioning the nitrogen oxides and ozone according to source category. The results have been compared with Pollution from Aircraft Emissions in the North Atlantic flight corridor (POLINAT 2) and Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX) airborne measurements in the North Atlantic flight corridor in 1997. Various cases have been investigated: measurements during a stagnant anticyclone and an almost cutoff low, both with expected high aircraft contributions, a southward bound flight with an expected strong flight corridor gradient and lightning contributions in the south, and a transatlantic flight with expected boundary layer pollution near the U.S. coast. The agreement between modeled results and measurements is reasonably good for NO and ozone. Also, the calculated impact of the three defined sources was consistent with the estimated exposure of the sampled air to these sources, obtained by specialized back trajectory model products. Model calculations indicate that aircraft contributes 55% to the mean NOx concentration and 10% to the O3 concentration in the North Atlantic flight corridor in October 1997, whereas lightning and surface emissions add 15% and 25% to the NOx concentration and 20% and 30% to the O3 concentration.

Observations and model calculations of jet aircraft exhaust products at cruise altitude and inferred initial OH emissions

Exhaust emissions of NO, HNO2, and HNO3 in the near-field plume of two B747 jet airliners cruising in the upper troposphere were measured in situ using the research aircraft Falcon of the Deutsches Zentrum fur Luft- und Raumfahrt. In addition, CO2 was measured providing exhaust plume dilution rates for the species. The observations were used to estimate the initial OH mixing ratio OH0 and the initial NO2/NOx ratio (NO2/NOx)0 at the engine exit and the combustor exit by comparison with calculations using a plume chemistry box model. From the two different plume events, and using two different model simulation modes in each case, we inferred OH emission indices EI(OH) = 0.32–0.39 g (kg fuel)−1 (OH0 = 9.0–14.4 ppmv) and (NO2/NOx)0 = 0.12–0.17. Furthermore, our results indicate that the chemistry of the exhaust species during the short period between the combustion chamber exit and the engine exit must be considered with respect to the amount of OH at the engine exit plane because OH is already consumed to a great extent in this engine section because of conversion to HNO2 and HNO3. For the engines discussed here the modeled OH concentration decreases by a factor of ∼350 between combustor exit and engine exit, leading to OH concentrations of 1–2 × 1012 molecules cm−3 (= 0.3–0.7 ppmv) at the engine exit.

Regional nitric oxide enhancements in the North Atlantic flight corridor observed and modeled during POLINAT 2-A case study

In situ measurements of nitrogen oxides and other trace chemicals were performed aboard the DLR Falcon in September and October 1997 during POLINAT 2 over the eastern North Atlantic in areas with predicted high impact of aircraft emissions to search for flight corridor effects. During survey flights in the upper troposphere from the centre of the flight corridor to regions south of or below the major transatlantic aircraft routes, large-scale enhancements in mixing ratios of NO of about 50 to 150 pptv were observed in corridor areas compared to the NO abundance measured outside the corridor. Using simultaneous tracer measurements, back trajectory analyses for the air masses sampled, the actual distribution of the North Atlantic air traffic, and comparisons of observed and predicted NO distributions from a regional model of simulations including or excluding aircraft emissions, these enhancements were attributed mainly to aircraft NOx.

In-flight measurement of aircraft non-methane hydrocarbon emission indices

Concentrations of non-methane hydrocarbons (NMHC) and CO were measured in exhaust plumes of the DLR experimental aircraft ATTAS equipped with Rolls Royce M 45H Mk501 engines. The emission indices (EI) of individual light NMHC were determined from ratios of NMHC and CO concentration enhancements measured in grab samples and the concurrent in-flight measurements of EI of CO by FTIR emission spectroscopy. Alkenes and alkynes generated by cracking of larger NMHC molecules and aromatic compounds originating from unburnt fuel constituted a larger and a smaller fraction of the NMHC emissions, respectively.