Plume Processes Research Articles

A suspended-particle rosette multi-sampler for discrete biogeochemical sampling in low-particle-density waters

To enable detailed investigations of early stage hydrothermal plume formation and abiotic and biotic plume processes we developed a new oceanographic tool. The Suspended Particulate Rosette sampling system has been designed to collect geochemical and microbial samples from the rising portion of deep-sea hydrothermal plumes. It can be deployed on a remotely operated vehicle for sampling rising plumes, on a wire-deployed water rosette for spatially discrete sampling of non-buoyant hydrothermal plumes, or on a fixed mooring in a hydrothermal vent field for time series sampling. It has performed successfully during both its first mooring deployment at the East Pacific Rise and its first remotely-operated vehicle deployments along the Mid-Atlantic Ridge. It is currently capable of rapidly filtering 24 discrete large-water-volume samples (30–100 L per sample) for suspended particles during a single deployment (e.g. >90 L per sample at 4–7 L per minute through 1 μm pore diameter polycarbonate filters). The Suspended Particulate Rosette sampler has been designed with a long-term goal of seafloor observatory deployments, where it can be used to collect samples in response to tectonic or other events. It is compatible with in situ optical sensors, such as laser Raman or visible reflectance spectroscopy systems, enabling in situ particle analysis immediately after sample collection and before the particles alter or degrade.

Relationship between photochemical ozone production and NOx oxidation in Houston, Texas

An instrumented aircraft was used to study anthropogenic emissions and subsequent ozone and reactive nitrogen photochemistry in the continental boundary layer downwind of Houston, Texas. Measurements of ozone, carbon monoxide, NOx, and NOx oxidation products were conducted from the NOAA WP‐3 aircraft during the 2006 Texas Air Quality Study under a variety of meteorological conditions. Sixty‐five crosswind transects of plumes from Houston urban and industrial areas performed on 10 daytime flights from 13 September to 6 October 2006 are examined. Coincident measurements of NOx and its oxidation products show that NOx was oxidized predominately to nitric acid and peroxy acyl nitrates on time scales of a few hours. The observed relationships between O3 and NOx oxidation products are affected by both photochemistry and mixing of different air masses. On four flights, background pollutant mixing ratios were constant and CO to NOy enhancement ratios in downwind plume transects remained at the emission ratio. The enhancement ratio of O3 to NOx oxidation products was also nearly constant and could be used to derive ozone production efficiency (OPE) in plumes downwind from the Houston area. On the other flights, variable mixing of regionally polluted background air with plumes caused CO to NOy and O3 to NOy − NOx enhancement ratios to increase as plumes were transported. In such cases, enhancement ratios do not solely reflect plume processing, and OPE could not be determined. The OPE averages 5.9 ± 1.2 in coalesced plumes from urban and petrochemical industrial sources in Houston, with higher values in isolated plumes downwind from petrochemical facilities located along the Houston ship channel.

Lagrangian analysis of low altitude anthropogenic plume processing across the North Atlantic

Abstract. The photochemical evolution of an anthropogenic plume from the New-York/Boston region during its transport at low altitudes over the North Atlantic to the European west coast has been studied using a Lagrangian framework. This plume, originally strongly polluted, was sampled by research aircraft just off the North American east coast on 3 successive days, and then 3 days downwind off the west coast of Ireland where another aircraft re-sampled a weakly polluted plume. Changes in trace gas concentrations during transport are reproduced using a photochemical trajectory model including deposition and mixing effects. Chemical and wet deposition processing dominated the evolution of all pollutants in the plume. The mean net photochemical O3 production is estimated to be −5 ppbv/day leading to low O3 by the time the plume reached Europe. Model runs with no wet deposition of HNO3 predicted much lower average net destruction of −1 ppbv/day O3, arising from increased levels of NOx via photolysis of HNO3. This indicates that wet deposition of HNO3 is indirectly responsible for 80% of the net destruction of ozone during plume transport. If the plume had not encountered precipitation, it would have reached Europe with O3 concentrations of up to 80 to 90 ppbv and CO between 120 and 140 ppbv. Photochemical destruction also played a more important role than mixing in the evolution of plume CO due to high levels of O3 and water vapour showing that CO cannot always be used as a tracer for polluted air masses, especially in plumes transported at low altitudes. The results also show that, in this case, an increase in O3/CO slopes can be attributed to photochemical destruction of CO and not to photochemical O3 production as is often assumed.

Secondary shock wave in laser-material interaction

In this work, the effects of shock driven process of the laser-ablated argon plume in a background gas environment are explored via molecular dynamics simulations. The primary shock wave propagation and its influence on the backward motion of the target material are delineated. It is observed that the strong pressure gradient inside the main shock wave overcomes the forward momentum of the plume and some compressed gas, leading to backward movement and redeposition on the target surface. Reflection of the backward moving gas on the target surface results in the secondary shock wave. Detailed investigation of the secondary shock wave phenomenon is provided, which gives, for the first time, an insight into formation and evolution of the internal gaseous shock at the atomistic level.

An investigation on spill plume temperature of large space building fires

In fire safety engineering, rapid fire detection and suppression in large spaces are very important issue. Development of new techniques is always based on the good understanding of the basic principle of smoke movement, especially the temperature of spill plume. Aiming to this objective, this paper specifies the multi-sectional characteristics on spill plume free developing out of a wide-door cabin in a large space atrium by means of full-scale experiment, theoretical analysis and CFD modeling. First the physical development process of the spill plume is analyzed from the horizontal curved regime at the door, the near-field two-dimensional linear plume regime, through to the far-field axisymmetric plume regime. It demonstrates the coupling correlation existing between the linear virtual origin, critical transition height from linear to axisymmetric regime, the axisymmetric virtual origin and other parameters, such as the spill plume depth at the door, the mass and heat flow rate outside the cabin door, the cabin door width and height etc. The basic mathematic equations regarding each regime's centerline temperature have been obtained. The virtual origin position of linear plume regime and axisymmetric plume regime are given, the critical transition height of spill plume from the two-dimensional linear plume to axisymmetric plume regime is also proposed, and finally the double-part prediction model (MEDP) for the spill plume centerline temperature is put forward. By validation with the full-scale experiment and the large eddy CFD modeling, it shows that the proposed spill plume model is capable to well describe the centerline temperature varying characteristics of the spill plume free developing out of the cabin.

Effect of plume processes on aircraft impact

A versatile Gaussian plume model has been developed and used to investigate the chemistry in expanding aircraft plumes for a wide range of conditions, including the plume expansion rate, the composition of the background atmosphere, and the total time of the plume integration. The dependence of plume processing on altitude, latitude and season has been investigated in order to generate plume parameterizations for use in global models. Two different parameterizations have been compared. The results of the two parameterizations have been incorporated into a global model to assess the importance of plume processing on calculated aircraft impact. In contrast to a previous plume study, which found reductions of 20–35% in aircraft‐induced NOx at cruise altitude and 10–12% smaller column ozone changes at northern midlatitudes when plume effects were incorporated, results from the present study suggest that plume processing has only a small effect on the calculated aircraft impact on ozone at subsonic cruise altitudes. Both plume parameterizations gave small changes in ozone perturbations, suggesting that differences between previous modeling studies are not due primarily to the different parameterizations used in those studies.

Identification of a reactive degradation zone at a landfill leachate plume fringe using high resolution sampling and incubation techniques

Vertical small-scale variation in phenoxy acid herbicide degradation across a landfill leachate plume fringe was studied using laboratory degradation experiments. Sediment cores (subdivided into 5 cm segments) were collected in the aquifer and the sediment and porewater were used for microcosm experiments (50 experiments) and for determination of solid organic carbon, solid–water partitioning coefficients, specific phenoxy acid degraders and porewater chemistry. Results from a multi-level sampler installed next to the cores provided information on the plume position and oxygen concentration in the groundwater. Oxygen concentration was controlled individually in each microcosm to mimic the conditions at their corresponding depths. A highly increased degradation potential existed at the narrow plume fringe (37.7 to 38.6 masl), governed by the presence of phenoxy acids and oxygen. This resulted in the proliferation of a microbial population of specific phenoxy acid degraders, which further enhanced the degradation potential for phenoxy acids at the fringe. The results illustrate the importance of fringe degradation processes in contaminant plumes. Furthermore, they highlight the relevance of using high-resolution sampling techniques as well as controlled microcosm experiments in the assessment of the natural attenuation capacity of contaminant plumes in groundwater.

About this title

The seismically and volcanically active East African Rift System is an ideal laboratory for continental break-up processes: it encompasses all stages of rift development. Its northernmost sectors within the Afar volcanic province include failed rifts, nascent seafloor spreading, and youthful passive continental margins associated with one or more mantle plumes. A number of models have been proposed to explain the success and failure of continental rift zones, but there remains no consensus on how strain localizes to achieve rupture of 125–250 km thick plates, or on the interaction between the plates and asthenospheric processes. This collection of papers provides new structural, stratigraphic, geochemical and geophysical data and numerical models needed to resolve fundamental questions concerning continental break-up and mantle plume processes. It focuses on how mantle melt intrudes and is distributed through the plate, and how this magma intrusion process controls along-axis segmentation and facilitates break-up.

Diagenesis of oxyanions (V, U, Re, and Mo) in pore waters and sediments from a continental margin

This research tests the hypothesis that trace metals respond to the extent of reducing conditions in a predictable way. We describe pore water and sediment measurements of iron (Fe), manganese (Mn), vanadium (V), uranium (U), rhenium (Re), and molybdenum (Mo) along a transect off Washington State (USA). Sediments become less reducing away from the continent, and the stations have a range of oxygen penetration depths (depth to unmeasurable O 2 concentration) varying from a few millimeters to five centimeters. When oxygen penetrates ∼1 cm or less, Fe is reduced in the pore waters but reoxidized near the sediment-water interface, preventing a flux of Fe 2+ to overlying waters, whereas Mn oxides are reduced and Mn 2+ diffuses to overlying waters. Both Re and U authigenically accumulate in sediments. Only at the most reducing location, where the oxygen penetrates 0.3 cm below the sediment-water interface, does the surface 30 cm of sediments become reducing enough to authigenically accumulate Mo. Stations in close proximity to the Juan de Fuca Ridge crest are enriched in Mn and Fe from hydrothermal plume processes. Both V and Mo clearly associate with Mn cycling, whereas U may be associating with either Mn oxides and/or Fe oxyhydroxides. Rhenium is uncomplicated by adsorption to Mn oxides and/or Fe oxyhydroxides, and Re accumulation in sediments appears to be due solely to the extent of reducing conditions. Therefore, authigenic sediment Re enrichment appears to be the best indicator for intermediate reducing conditions, where oxygen penetrates less than ∼1 cm below the sediment-water interface, when coupled with negligible authigenic Mo enrichment.

Advantages of using adaptive remeshing and parallel processing for modelling biodegradation in groundwater

Biodegrading plumes in groundwater are often typified by relatively reactive zones around the fringes and less reactive zones in the core. A high degree of refinement is required at the fringes if a model is to be of use in improving the conceptual understanding of plumes. Two strategies for dealing with the potentially high computational demands are (i) parallel processing, where the workload is shared between multiple processors, and (ii) locally adaptive remeshing, where a refined area of the grid tracks the moving plume fringes through the domain. The partial differential equation toolbox, UG (Unstructured Grids) offers advanced numerical tools including adaptive remeshing, sparse matrix storage schemes, and multigrid solvers. It embraces many of these features within a parallel processing environment. This paper reports on a recent development of UG to simulate field scale reactive biogeochemistry including Monod kinetics, NAPL dissolution, mineral precipitation/dissolution and ion exchange. The non-linear multicomponent reactive transport system is solved with the fully coupled method. Test cases have been used for verification of the new capability. The paper illustrates an application to a 3D field site. It is demonstrated that both adaptive remeshing and parallel processing can improve efficiency and in turn facilitate the incorporation of a more complex set of species and reactions such that understanding of plume processes is enhanced.

Three Dimensional Monitoring of Stack Plume Dynamics by a Scanning Mie Lidar System as a Plume Watchdog Station

A scanning lidar system was developed to watch the nighttime diffusion process of plume from a smokestack of a large incinerator located around 3 km from the system. Observed data sets were visualized as three dimensional images in which could be seen the diffusion pattern from any direction, and this made it easy to investigate the exhaust dynamics. Observation results showed that the original plume extended at least 1.6 km, where there was a residential area, from the smokestack increasing in diameter to about 500 m. High density aerosols originating from the smokestack were measured in that area even at midnight. The lidar system performance as a plume watchdog station was discussed from the standpoint of publichealth-related plume monitoring.

Evolution of particle number distribution near roadways. Part III: Traffic analysis and on-road size resolved particulate emission factors

On-road size-resolved particulate emission factors were computed using concurrently measured carbon monoxide (CO) as a freeway dilution indicator and correlating roadside particle measurements to CO measurements. The emission factors derived for the total particle number agree well with previous on-road investigations. However, this study extends this analysis to produce unique receptor-dependent, size-resolved, road and grid-level emission factor distributions. Both mileage- and fuel-based particle number and mass emission factors at road and grid levels, along with CO emission factors, are presented and the results from freeways with distinctly different percentages of heavy-duty diesel truck traffic are compared. The effects of plume processing on particle number near roadways are shown to be much more profound than on particle mass, further indicting that the adverse health effects observed near roadways are at least partially related to particle numbers.

Grand Comore Island: A well-constrained “low 3He/ 4He” mantle plume

We report He isotope ( 3He/ 4He) variations in samples from alkali basaltic and basanitic lava flows from Grande Comore Island complemented by existing [1,2] [C. Class, S.L. Goldstein, Plume–lithosphere interactions in the ocean basins: constraints from the source mineralogy. Earth Planet. Sci. Lett., 150 (1997) 245–260, C. Class, S.L. Goldstein, R. Altherr, P. Bachèchlery, The process of plume–lithosphere interaction in the ocean basins—the case of Grande Comore. J. Petrol., 39 (5) (1998) 881–903] and new Sr–Nd–Pb isotope ratios and major and trace element abundances. He isotope data in samples from Tristan da Cunha and Gough islands and the Huri Hills in Kenya are reported also. Grande Comore 3He/ 4He ratios vary between 5.05 and 7.08 R A ( 4He/ 3He ≈ 141,000–101,000). Chemical and Sr–Nd–Pb isotopic variations of Grande Comore lavas were previously shown to reflect melts derived from the deep mantle plume and the shallow lithospheric mantle [1–3] [C. Class, S.L. Goldstein, Plume–lithosphere interactions in the ocean basins: constraints from the source mineralogy. Earth Planet. Sci. Lett., 150 (1997) 245–260, C. Class, S.L. Goldstein, R. Altherr, P. Bachèchlery, The process of plume–lithosphere interaction in the ocean basins-the case of Grande Comore. J. Petrol., 39 (5) (1998) 881–903, C. Claude-Ivanaj, B. Bourdon, C.J. Allègre, Ra–Th–Sr isotope systematics in Grande Comore Island: a case study of plume–lithosphere interaction. Earth Planet. Sci. Lett. 164 (1998) 99–117]. The lithosphere-dominated end-member (La Grille volcano) shows uniform 3He/ 4He ratios within error of 6.75–7.08 R A ( 4He/ 3He ≈ 106,000–101,000) over a range of [He] = 36–428 × 10 − 9 ccSTP/g. The plume end-member (of the Karthala volcano suite), as constrained by Sr, Nd, Pb isotope ratios, shows uniformly lower 3He/ 4He ratios with 5.05–5.41 R A ( 4He/ 3He ≈ 141,000–132,000) over a range of [He] = 11–136 × 10 − 9 ccSTP/g. All samples show good correlations between Sr–Nd–He isotope ratios, indicating that the Grande Comore 3He/ 4He ratios are not significantly influenced by crustal contamination and reflect recent mixing between plume- and lithosphere-derived melts. The lithosphere beneath Grande Comore has retained its MORB-like helium isotopic composition, which suggests that the previously identified amphibole-forming metasomatism of the lithospheric mantle [1] [C. Class, S.L. Goldstein, Plume–lithosphere interactions in the ocean basins: constraints from the source mineralogy. Earth Planet. Sci. Lett., 150 (1997) 245–260] occurred prior to the arrival of the Comoro plume. The well-constrained 3He/ 4He = 5.2 ± 0.2 R A ( 4He/ 3He ≈ 137,000 ± 5000) of the Comoro plume confirms the existence of “low 3He/ 4He” mantle plumes. A global compilation of OIB shows that OIB from “low 3He/ 4He” plumes form one “side” of the roughly triangular distribution of the global OIB data set in 143Nd/ 144Nd versus 206Pb/ 204Pb and 208Pb/ 204Pb, encompassing the lowest Nd to the highest Pb isotope ratios. It is also shown that “low 3He/ 4He” plumes are more enriched in Th and U relative to other plumes.

Microphysics and heterogeneous chemistry in aircraft plumes - high sensitivity on local meteorology and atmospheric composition

Abstract. An aircraft plume model has been developed on the basis of two coupled trajectory box models. Two boxes, one for plume and one for background conditions, are coupled by means of a mixing parameterization based on turbulence theory. The model considers comprehensive gas phase chemistry for the tropopause region including acetone, ethane and their oxidation products. Heterogeneous halogen, N2O5 and HOx chemistry on various types of background and aircraft-induced aerosols (liquid and ice) is considered, using state-of-the-art solubility dependent uptake coefficients for liquid phase reactions. The microphysical scheme allows for coagulation, gas-diffusive particle growth and evaporation, so that the particle development from 1s after emission to several days can be simulated. Model results are shown, studying emissions into the upper troposphere as well as into the lowermost stratosphere for contrail and non-contrail conditions. We show the microphysical and chemical evolution of spreading plumes and use the concept of mean plume encounter time, tl, to define effective emission and perturbation indices (EEIs and EPIs) for the North Atlantic Flight Corridor (NAFC) showing EEI(NOy) and EPI(O3) for various background conditions, such as relative humidity, local time of emission, and seasonal variations. Our results show a high sensitivity of EEI and EPIs on the exact conditions under which emissions take place. The difference of EEIs with and without considering plume processes indicates that these processes cannot be neglected.

The effect of plume processes on the Fe isotope composition of hydrothermally derived Fe in the deep ocean as inferred from the Rainbow vent site, Mid-Atlantic Ridge, 36°14′N

The Rainbow hydrothermal vent site, which is the largest known point source for dissolved Fe delivered to the deep North Atlantic ocean, has remained invariant in its Fe isotope composition over at least the past 16,000 years, based on analysis of metalliferous sediments beneath the plume. Because of the conservative behavior of Fe in the Rainbow plume, δ 56Fe values of particles in the neutrally buoyant plume (−0.18±0.05‰) and underlying sediments (−0.19±0.05‰) are indistinguishable from the δ 56Fe values of the high-temperature fluid sources (−0.23±0.04‰). Particles from the near-vent, buoyant stage of the plume, however, have higher δ 56Fe values (+0.15‰ to +1.20‰) relative to the original vent fluid, consistent with fractionation during oxidation of Fe(II) aq to Fe(III) aq. Isotope compositions become invariant in the plume once all Fe(II) aq is fully oxidized, preserving the original composition of the vent fluid. The constant Fe isotope compositions of the vent fluids over time implies that changes in seawater Fe isotope composition of the North Atlantic ocean, as they are recorded in Fe–Mn crusts, requires changes in the relative fluxes of Fe to the ocean.

Transformation of dissolved and particulate materials on continental shelves influenced by large rivers: plume processes

The world's ten largest rivers transport approximately 40% of the fresh water and particulate materials entering the ocean. The impact of large rivers is important on a regional/continental scale (e.g. the Mississippi drains ∼40% of the conterminous US and carries approximately 65% of all the suspended solids and dissolved solutes that enter the ocean from the US) and on a global scale (e.g. the Amazon River annually supplies approximately 20% of all the freshwater that enters the ocean; e.g. approximately 85% of all sedimenting organic carbon in the ocean accumulates in coastal margin regions). River plume processes are affected by a suite of complex factors that are not fully understood. It is clear however, that the composition, concentration and delivery of terrestrial materials by large rivers cannot be understood by simply scaling up the magnitudes and impacts of dominant processes in smaller rivers. Because of high rates of particulate and water discharge, the estuarine processes associated with major rivers usually take place on the adjacent continental shelf instead of in a physically confined estuary. This influences the magnitude and selectivity of processes that transform, retain or export terrestrial materials. Buoyancy is a key mediating factor in transformation processes in the coastal margin. In this paper we review and synthesize current understanding of the transformation processes of dissolved and particulate organic and inorganic materials associated with large river (buoyant) plumes. Chemical and biological activities are greatly enhanced by the changed physical and optical environment within buoyant plumes. Time and space scales over which these transformation processes occur vary greatly, depending on factors such as scales of discharge, suspended sediment loads, light and temperature. An adequate understanding of transformation processes in these highly dynamic, buoyancy-driven systems is lacking. In this paper, we review the biogeochemical processes that occur in large river plumes.

Hydrothermal fluxes at mid-ocean ridges and on ridge flanks

Hydrothermal fluxes of heat and mass at mid-ocean ridges and on ridge flanks estimated using different approaches are reviewed. Heat and fluid fluxes in high temperature axial systems are best determined by geophysical methods, and are then combined with vent fluid compositions to derive chemical fluxes. Axial chemical fluxes calculated by mass balance using data from hydrothermally altered rocks sampled by deep ocean drilling are generally small, probably because of loss of material during drilling. Most of the hydrothermal heat anomaly in ocean crust occurs at low temperatures in off-axis flank systems, and a significant fraction of this must occur at very low temperatures (<25 °C). Flank processes enhance the axial fluxes of some elements, but offset and cancel the axial fluxes of others. Processes in hydrothermal plumes are also important in determining the net chemical fluxes in MOR systems. To cite this article: J.C. Alt, C. R. Geoscience 335 (2003).

Chloride Ion in Groundwater near Disposal of Solid Wastes in Landfills

To study the influence of leachate plume from sanitary landfills on groundwater, the concentration of chloride ion in the groundwater, soil water, and river water are observed because chloride ion is nonreactive and not sorptive and has no redox or precipitation. The experimental result indicates the flow process of the leachate plume near the landfills; that is, most of the leachate plume is discharged into a river, and the remainder infiltrates into the ground, especially through the weathered geological layer. Although small values of saturated hydraulic conductivity in the geological layer near the landfills hold back the leachate plume of chloride ion from the two sources, this study also notes the existence of two sources of chloride ion near the landfills: one is the rice field, and the other is the landfills themselves.

Size-Resolved Characterisation of Soluble Ions in the Particles in the Tropospheric Plume of Masaya Volcano, Nicaragua: Origins and Plume Processing

We present the first application of a multi-stage impactor to study volcanic particle emissions to the troposphere from Masaya volcano, Nicaragua. Concentrations of soluble SO42−,Cl−, F−, NO3−, K+, Na+,NH4+, Ca2+ and Mg2+ were determined in 11 size bins from ∼0.07 μm to >25.5 μm. The near-source size distributions showed major modes at 0.5μm (SO42−, H+,NH4+); 0.2 μm and 5.0 μm (Cl−) and 2.0–5.0 μm(F−). K+ and Na+ mirrored the SO42− size-resolvedconcentrations closely, suggesting that these were transported primarily asK2SO4 and Na2SO4 in acidic solution, while Mg2+ andCa2+ presented modes in both 1 μm particles. Changes in relative humidity were studied by comparing daytime (transparent plume) and night-time (condensed plume) results. Enhanced particle growth rates were observed in the night-time plume as well as preferential scavenging of soluble gases, such as HCl, by condensed water. Neutralisation of the acidic aerosol by background ammonia was observed at the crater rim and to a greater extent approximately 15 km downwind of the active crater. We report measurements of re-suspended near-source volcanic dust, which may form a component of the plume downwind. Elevated levels ofSO42−, Cl−, F−,H+, Na+, K+ and Mg2+ were observed around the 10 μm particle diameter in this dust. The volcanic SO42− flux leaving the craterwas ∼0.07 kg s−1.

Impacts of NOx emissions from subsonic aircraft in a global three‐dimensional chemistry transport model including plume processes

A three‐dimensional (3‐D) global chemistry transport model (CTM) has been used to study the impact of NOx emissions from subsonic aircraft on the NOx and ozone concentrations in the troposphere. Plume scale processes have been included by a dispersion model which modifies the NOx emissions to include formation of nitrogen reservoir species and nonlinear chemical effects on ozone production and loss within the plume regime. These modifications were varied as a function of time of day of emissions, latitude, season, temperature, atmospheric turbulence and background concentrations of NOx and ozone. With a global emission rate of 0.7 Tg(N) yr−1 from aircraft and including plume scale effects in the 3‐D CTM, we estimate a maximum ozone perturbation at 250 hPa from 5.5 to 10.5 ppbv north of 40°N in May. In January the maximum is lower (3–4 ppbv) and more confined to a zonal band between 35 and 50°N. During July the influence of vertical mixing is found to reduce the maximum at midlatitudes, and the largest perturbations (6.5–8 ppbv) are found in the polar region. The use of modified aircraft emissions had a significant influence on the estimated NOx and ozone increases, and the largest effects were found in May. Compared with an unmodified NOx emission from aircraft, the NOx perturbations at cruise altitude decreased by 25–35% over the eastern U.S., the North Atlantic Ocean, and Europe. The corresponding decrease in the ozone perturbation was 15–18% at northern middle and high latitudes.