Objectives

Concept

Data Evaluation

Results

Access to the Database

EU project POLINAT II

EU project TRADEOFF

Publications

Visit our photo gallery!

Objectives

NOXAR was aimed to produce a comprehensive data set of nitrogen oxide (NO and NO2) and ozone concentrations in the upper troposphere and the lower stratosphere as a significant step towards a climatology of these species. Nitrogen oxides are important precursors for ozone formation at the altitudes of current subsonic aircraft operation (typically at 9-12 km altitude). NOx emitted at these altitudes has a larger potential for O3 formation than NOx from ground sources. O3 is not only an essential component of the well known photochemical smog frequently forming over highly populated and industrialised areas in summer, it is also an important greenhouse gas with the largest efficiency in the tropopause region where most aircraft operation takes place.
The response of O3 concentrations to future increases in NOx due to the growing air traffic depends crucially on present background concentrations of NOx which are not well quantified until present. The NOXAR project was mainly aimed to bridge this gap.

Due to its comparatively high representativity and large geographical coverage, the NOXAR data set is particularly well suited to validate the NOx and O3 concentration fields calculated by chemical transport models (CTMs) which until today have been the only tools allowing to estimate the O3 increase caused by present and future air traffic emissions.
3D-CTM simulations for the NOXAR period have been carried out at the Royal Dutch Meteorological Institute (KNMI) in Holland and are still being evaluated. These simulations allow the direct comparison of model output with measurements, with the goal to improve the behaviour of the model regarding the difficult simulation of the NOx concentration field.

Furthermore, the NOXAR data set is well suited for studies of the budget of NOx in the upper troposphere and the lower stratosphere. Sources of NOx at these altitudes are:

- convective upward transport of NOx produced by ground sources
- NOx produced by lightning activity
- NOx emitted by aircraft
- downward mixing of NOx from the stratosphere where it is produced by the decomposition of N2O

The contribution from individual sources to the NOx burden at aircraft cruising altitudes is not yet well established (especially that of lightning and surface sources).
 

Concept

NOXAR was funded by the Swiss Federal Civil Aviation Authority (BAZL). A measuring system designed by ECO Physics Inc. in cooperation with our institute to measure ozone and nitrogen oxides (NO and NO2) was installed in the cargo compartment of a SWISSAIR airliner B­747.

The system was operated during one year (from May 1995 until May 1996) on about 500 scheduled flights to destinations in the United States (NY, Atlanta, Chicago, Boston) and the Far East (Beijing, Bombay, Hong Kong).

The system was operated fully automatically including automatic start-ups/shut-downs after take-off and before landing, respectively. The sensitivity and zero point drift of the analysers was automatically calibrated in-flight at regular time intervals.

Visit our photo gallery!

Design (top) of the NOXAR system and position (bottom) in the B-747.
Two NO analysers are placed on the bottom shelf of the rack. The
second NO analyser is used in combination with a photolytic converter
to measure the sum of NO+NO2(converted). A UV-photometer is used
to measure O3. The system is operated fully automatically governed by
the computer on the top shelf including automatic start-ups/shut-
downs and frequent calibrations of the analysers on each flight.

Data Evaluation

The concentrations of ozone, NO and NO2 as well as meteorological parameters provided by the aircraft data system (temperature, pressure, horizontal winds, vertical wind (calculated from attack angle, true airspeed, attitude angles and accelerations of the aircraft) are stored simultaneously with aircraft position and time (UTC) at a resolution of 3 sec for chemical parameters and at least 1 sec for meteorological parameters. For an easier handling of the large amount of data the records are also available as 2-min averages.

NO2 photodissociates to NO+O at wavelengths between about 300 and 400 nm. NO, NO2 and ozone at flight altitudes are roughly in photostationary equilibrium determined by the photolysis frequency J_NO2 (i.e. by the solar light intensitiy between 300-400 nm). The photolysis frequencies J_NO2 are calculated for all flights based on flight altitude, and solar zenith angle using the photolysis model STAR of the University of Munich, Germany. The NO2 data of the first half of the measuring period suffered from a contamination of the converter. Later measurements are close to the values expected from photostationary state calculations (though still higher by about 15 pptv or 30%). For the final climatology of NOx at cruise altitudes calculated NO2 values were used rather than the measured NO2 data. Since NO2 is on average only a small fraction of total NOx (about 20-30%), the uncertainty in NOx introduced by errors in the calculation of photostationary state NO2 is relatively small (of the order of 10-20%).

High resolution wind, temperature and humidity fields provided by the European Center for Medium Range Weather Forecast (ECMWF) model were interpolated in space and time to the flight tracks and the tropopause altitude was calculated from potential vorticity profiles (tropopause assumed at 1.5, 2 or 4 PVU respectively). These calculations were executed by Heini Wernli and Dominique Jeker.

4-day backward and foreward air parcel trajectories were calculated by Michel Bourqui from each position of the B-747 in the 2-min data records for the entire measuring period. The evaluation of this extensive set of trajectory data will provide very useful correlations between airmass histories and observed concentrations. These trajectories already proved very useful in a number of case studies of selected events of high NOx concentrations (e.g.

Some Results

Examples of the NOx* (=measured NO + calculated NO2) distribution observed in summer (June/July/August) and in winter (December, January, February) are shown below. The figures were created by first gridding all NOXAR measurements to a regular grid and then applying a 2D low-pass filter in order to suppress features smaller than synoptic scales and to make the results comparable to model outputs.

Distribution of NOx* (ppbv) averaged over the altitude range 9-12 km in summer (JJA)
1995 as measured by NOXAR

Distribution of NOx* (ppbv) averaged over the altitude range 9-12 km in winter (DJF)
1995/1996 as measured by NOXAR
 

Important sources of nitrogen oxides at tropopause altitudes in addition to air traffic are lightning activity and rapid vertical transport of NOx emitted at the ground by industry, traffic, biomass burning and microbial soil activity. Trajectory calculations are an important tool for airmass classification and allow to trace back possible contributions from lightning or ground sources as demonstrated below.

Click on image for better view (340 kb)
5-day backward trajectories from a part of the flight track where extremely
high NOx concentrations were observed. The air parcel trajectories are plotted
over a NOAA satellite image create approximately 12 h prior to the flight.
 

Example of 5 day backward trajectories starting along a section of the flight path from Zurich to Beijing where extremely high NOx concentrations were observed over a distance of several hundred kilometers. The image shows the region over Siberia/Russia. The Kaspian and the Black Sea are visible near the centre of the image. The Mediterranean is visible at the lower left corner. The air parcels follow a path from left to right along an upper level trough which is connected to the depression clearly visible in the satellite image to the north of the Kaspian Sea. The air parcel trajectories pass over a region of heavy thunderstorms about 24 hours before they reach the flight track of the B-747. In the satellite image shown above  this region is displaced somewhat to the left of the trajectories and highlighted by red colors in the full resolution image. It is believed that lightning activity and/or upward transport in convective clouds observed over more than one day along the cold front connected to the depression is responsible for the high NOx concentrations detected at 11 km altitude.

Short NOx peaks (< 1-2 min) of a few ppb were frequently observed when the B-747 crossed the exhaust plume of another aircraft in the flight corridor. Data of aircraft movements in the North-Atlantic region (Shanwick air control region, Shanwick=Shannon (Ireland) and Prestwick (Scotland)) were provided by the Scottish & Oceanic Area Control Centre (NATS) and may help to trace back the source aircraft of observed plumes.

Access to the NOXAR database

The NOXAR data are archived in the NASA data format developped by R. S. Hipskind and S. E. Gaines. A brief overview of the archive is given here . Please contact Dominik Brunner  for details.

The NOXAR archive is accessible from Louisa Emmons' "Data Composites of Tropospheric Ozone and Its Precursors" website at the University of Michigan. A large compilation of other aircraft measurement campaign data can also be found there.

Data of the 1997 campaign have been archived at DLR and NASA Ames and are available for members of the POLINAT-2 and SONEX community only (see POLINAT and SONEX links below).

POLINAT II

Since 1997 NOXAR is part of the EU-Project POLINAT-II (Pollution from Aircraft Emissions in the North Atlantic Flight Corridor).

The NOXAR system was operated during 3 months as part of the POLINAT-II campaign in autumn 1998. This campaign was co-ordinated with NASA's SONEX experiment.

With the method of lightning tracing (which was developed in cooperation with the team of SONEX) we showed for the first time that - in some cases - the number of lightning flashes accumulated along back trajectories was proportional to the NOx concentrations observed several hundred kilometers downward of the anvil outflows.

TRADEOFF

In the EU project TRADEOFF (Aircraft emissions: Contributions of various climate compounds to changes in composition and radiative forcing - tradeoff to reduce atmospheric impact) we construct climatologies of several different trace species including NOx from all available measurements in the upper troposphere and the lower stratosphere between 1995 and 1998. This climatology will be used in the TRADEOFF community for comparison with numerical simulations which are widely used to assess the influence of anthropogenic NOx emissions on troposheric ozone and climate.

D. Brunner, J. Staehelin, D. Jeker, H. Wernli, and U. Schumann, Nitrogen oxides and ozone in the tropopause region of the Northern Hemisphere Measurements from commercial aircraft in 1995/96 and 1997, J. Geophys. Res., 106, 27673-27699, 2001.

V. Grewe, D. Brunner, M. Dameris, J.L. Grenfell, R. Hein, D. Shindell, and J. Staehelin, Origin and variability of upper tropospheric nitrogen oxides and ozone at northern mid-latitudes, Atmospheric Environment, 35, 3421-3433, 2001.
Abstract

L. K. Emmons, D. A. Hauglustaine, J.-F. Mueller, M.A. Carroll, G.P. Brasseur, D. Brunner, J. Staehelin, V. Thouret, and A. Marenco, Data composites of airborne observations of tropospheric ozone and its precursors, J. Geophys. Res., 105, 20497-20538, 2000.
PDF

D. P. Jeker, L. Pfister, A. M. Thompson, D. Brunner, K. E. Pickering, D. J. Boccippio, H. Wernli, Y. Kondo, and J. Staehelin, Measurements of nitrogen oxides at the tropopause - attributions to convection and correlation with lightning, J. Geophys. Res., 105, 3679-3700, 2000.

D. P. Jeker, Nitrogen oxides and ozone measurements at the tropopause and attributions to convection and lightning, PhD thesis, 1999, ETH Zürich, Switzerland.

Intergovernmental Panel on Climate Change (IPCC), Aviation and the global atmosphere, edited by J.E. Penner, Cambridge Univ. Press, New York, 1999.

World Meteorological Organisation (WMO), Scientific assessment of ozone depletion: 1998, Report No. 44, Geneva, Switzerland.

D. Brunner, J. Staehelin, and W. Moser, Planned Measurements of NO, NO2 and O3 from a SWISSAIR airliner. In Impact of Emissions from Aircraft and Spacecraft Upon the Atmosphere, Proc. of an International Colloquium, Cologne, April 18-20, 1994, pp 36-41.

P. Dias-Lalcaca, D. Brunner, W. Imfeld, W. Moser, and J. Staehelin, An Automated System for the Measurement of Nitrogen Oxides and Ozone Concentrations from a Passenger Aircraft: Instrumentation and First Results of the NOXAR Project. Environmental Science & Technology 32(20), 3228-3236, 1998.

D. Brunner, One-year climatology of nitrogen oxides and ozone in the tropopause region - results from B-747 aircraft measurements. Ph.D. thesis No. 12556, ETH Zurich, Switzerland.

D. Brunner, J. Staehelin, and D. Jeker, Large-scale Nitrogen Oxide Plumes in the Tropopause Region and Implications for Ozone. Science, 282, 1305-1309, 1998.

Swissair Gazette Nr. 5/97, 15-16, 1997.

Swissair Gazette Nr. 3/96, 77-79, 1996.

MOZAIC-III workshop, Toulouse, November 13-14, 2000.

Several POLINAT workshops held at: DLR (Oberpfaffenhofen, Germany), Ecole Polytechnique (Paris, France), NILU (Oslo, Norway), ETH Zurich (Switzerland)

The 1999 Conference on the Atmospheric Effects of Aviation. Virginia Beach, USA, April 18 -April 23, 1999 (oral presentation)

The 1998 Conference on the Atmospheric Effects of Aviation. Virginia Beach, USA, April 27-May 1, 1998 (oral presentation)

The 1997 Conference on the Atmospheric Effects of Aviation. Virginia Beach, USA, March 10-14, 1997 (oral presentation)

European Geophysical Society (EGS) Conference 1996. The Hague, Netherlands, May 6-10, 1996 (oral presentation)

Impact of Emissions from Aircraft and Spacecraft Upon the Atmosphere. An International Colloquium, Cologne, Germany, April 18-20, 1994 (poster presentation)

EUROTRAC Symposium '94. Transport and Transformation of Pollutants in the Troposphere, Garmisch-Partenkirchen, Germany, April 11-15 1994 (poster presentation)

Institute for Atmospheric and Climate Science

Swissair Corporate Communications
P.O. Box
CH-8058 Zurich-Airport
e-mail: info@swissair.com
phone +41 1 812 44 52
fax +41 1 812 90 00

For further information please contact the head of the NOXAR project Johannes Staehelin.
For questions concerning this webpage contact the webmasters D. Brunner or D. Jeker.