Philippe Nédélec

Measurement of ozone and water vapor by Airbus in-service aircraft: The MOZAIC airborne program, an overview

Tentative estimates, using three-dimensional chemistry and transport models, have suggested small ozone increases in the upper troposphere resulting from current aircraft emissions, but have also concluded to significant deficiencies in todays models and to the need to improve them through comparison with extended data sets. The Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program was initiated in 1993 by European scientists, aircraft manufacturers, and airlines to collect experimental data. Its goal is to help understand the atmosphere and how it is changing under the influence of human activity, with particular interest in the effects of aircraft. MOZAIC consists of automatic and regular measurements of ozone and water vapor by five long range passenger airliners flying all over the world. The aim is not to detect direct effects of aircraft emissions on the ozone budget inside the air traffic corridors but to build a large database of measurements to allow studies of chemical and physical processes in the atmosphere, and hence to validate global chemistry transport models. MOZAIC data provide, in particular, detailed ozone and water vapor climatologies at 9–12 km where subsonic aircraft emit most of their exhaust and which is a very critical domain (e.g., radiatively and stratosphere/troposphere exchanges) still imperfectly described in existing models. This will be valuable to improve knowledge about the processes occuring in the upper troposphere and the lowermost stratosphere, and the model treatment of near tropopause chemistry and transport. During MOZAIC I (January 1993–September 1996), fully automatic devices were developed, installed aboard five commercial Airbus A340s, and flown in normal airline service. A second phase, MOZAIC II, started in October 1996 with the aim of continuing the O3 and H2O measurements and doing a feasibility study of new airborne devices (CO, NOy). Between September 1994 and December 1997, 7500 flights, representing 54,000 flight hours, were made over the continents (Europe, North America, Asia, South America, and Africa) and the Atlantic Ocean. Most of the measurements (90%) correspond to cruise altitudes (9–12 km), the remaining being obtained during ascents and descents near the 50 cities frequented by MOZAIC operations. This paper reports the main characteristics of the program and the flights, with a brief summary of the general content and focus of papers already published and companion papers of this special issue. These deal with the following: description and validation of the ozone and water vapor measurement methods; presentation of an accurate ozone climatology at 9–12 km altitude, over the Northern Hemisphere (130°W–140°E; 0°–80°N), and down to 30°S over South America and Africa; comparison between a 2-year MOZAIC ozone climatology (1994–1996; 0–12 km) and a long series of older measurements made since the 1980s at 8 stations of the Ozone Sounding Network; study of ozone-rich transients, up to 500 ppbv on a horizontal scale of 5–80 km, in the upper tropical troposphere; and comparison between MOZAIC ozone data and output from the global chemistry and transport model (CTM) TOMCAT.

Evidence of a long-term increase in tropospheric ozone from Pic du Midi data series: Consequences: Positive radiative forcing

The rate at which ozone is increasing in the troposphere is uncertain due to the lack of accurate long-term measurements. Old ozone measurements obtained at the Pic du Midi Observatory (3000 m high, southwestern France) were recently rediscovered. Four sets of data available at this station are presented herein: (1) 1874–1881 and (2) 1881–1909 by the Schonbein method and (3) 1982–1984 and (4) 1990–1993 by UV absorption analyzers. The results show an increase in ozone by a factor of 5 since the beginning of the twentieth century, corresponding to an exponential increase of 1.6% per year, although this trend is probably higher (2.4% per year) for the last few decades. A stable 10 ppb ozone mixing ratio is observed during the first 20 years of the series, which is representative of the preindustrial era ozone level. The increase is seen to start around 1895. Other data, obtained at various European high-altitude stations between 1920 and 1980, tie in closely with the Pic du Midi observations. A tentative evaluation of the impact of tropospheric ozone on radiative forcing confirms that ozone is currently the second most significant greenhouse gas, responsible for 22% and 13% of radiative forcing changes since 1800 in the northern and southern hemispheres, respectively. If these rates were to be maintained in the future, ozone would continue to evolve differently in the two hemispheres (maximum level in the northern hemisphere) and could make an even more significant contribution to the radiative forcing of the northern hemisphere.

Comparisons of ozone measurements from the MOZAIC airborne program and the ozone sounding network at eight locations

Automatic ozone measuring devices have been operating continuously on board the five long-range aircraft of the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program since September 1994. This paper presents the main characteristics of the ozone system and the procedures followed to ensure its accurate calibration over long durations. Measurement accuracy was estimated at ±[2 ppbv + 2%], but much better in-flight levels were in fact observed: average discrepancy (between different devices) ranging from 1 ppbv at tropospheric concentrations to a few ppbv at stratospheric concentrations. This demonstrates the ability of the MOZAIC ozone data to produce accurate and reliable ozone climatologies. A 2-year ozone climatology (1994–1996) generated from MOZAIC data collected at between O and 12 km altitude was compared to longer and older measurements made at eight stations of the Ozone Sounding Network (OSN): Hohenpeissenberg, Wallops Island, Tateno, Palestine, Pretoria, Goose Bay, Biscarosse, and Poona. Despite the different nature of the programs (techniques, platforms, sampling frequencies, spatial distribution, and operation periods), the OSN and MOZAIC climatologies were found to show a reasonably high level of agreement. Mean concentrations derived from ozone sondes are about 3 to 13% higher than those obtained by the MOZAIC program in the free troposphere, in a similar geographic location. These differences are within the range of uncertainty of the two techniques. Larger discrepancies observed in the boundary layer and in upper layers are explained by the influence of local pollution and the distance between measurements, amongst other factors, limiting the reliability of comparisons. A comparison of OSD and MOZAIC data at Hohenpeissenberg/Frankfurt and Wallops Island/New York, over an overlapping period (1994–1995), shows good agreement in the free troposphere (800–300 hPa), no detectable bias for Hohenpeissenberg/Frankfurt, when taking into consideration the various causes of discrepancies (Dobson normalization, ozone geographical variations). Indeed, the results of this analysis support the hypothesis that it is not advantageous to scale the ozone sonde data to the overhead ozone column; the scaling appears to cause overestimation of the tropospheric O3 concentrations, by about 3–6% at Hohenpeissenberg, and to cause more scatter in the sonde-MOZAIC differences. The correspondence between the OSN and MOZAIC climatologies obtained in very different conditions demonstrates that they are representative of the atmosphere and that, being complementary while each retains its own advantages, they are therefore both useful for validation studies.

Ozone climatologies at 9–12 km altitude as seen by the MOZAIC airborne program between September 1994 and August 1996

From data collected at cruise levels by the five aircraft of the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program during a 2-year period (September 1994 to August 1996), an accurate ozone climatology at 9-12 km altitude has been generated over the northern hemisphere (130°W-140°E; 0°-80°N), and down to 30°S over South America and Africa. North of 35°N, the distribution is dominated by the influence of ozone-rich air of stratospheric origin; farther south, ozone-poor air from the troposphere prevails. A classification based on a threshold of 100 ppbv of ozone is used to distinguish between the stratospheric and tropospheric components and to help in interpreting the data. Seasonal variations of ozone are observed in stratospheric air (maximum in spring, minimum in winter) and in tropospheric air (maximum in summer, minimum in autumn), related to the intensities of dynamic (tropopause variations; stratosphere/troposphere exchanges) and chemical (photochemistry) processes. The tropics exhibit variations that are heterogeneous in time and space, and reflect the influences of active photochemical processes, deep convection and biomass burning emissions. Ozone concentrations decrease with latitude in both the stratosphere and troposphere. A strong vertical gradient is found in stratospheric air but not in tropospheric air, which is much more homogeneous. The integration of data over characteristic geographical areas shows smaller concentrations over the Atlantic Ocean compared to the continents; this is related to the zonal variation of the polar front and the position of ridge/trough pressure systems.

Air pollution during the 2003 European heat wave as seen by MOZAIC airliners

This study presents an analysis of both MOZAIC profiles above Frankfurt and Lagrangian dispersion model simulations for the 2003 European heat wave. The comparison of MOZAIC measurements in summer 2003 with the 11-year MOZAIC climatology reflects strong temperature anomalies (exceeding 4 C) throughout the lower troposphere. Higher positive anomalies of temperature and negative anomalies of both wind speed and relative humidity are found for the period defined here as the heat wave (2–14 August 2003), compared to the periods before (16–31 July 2003) and after (16–31 August 2003) the heat wave. In addition, Lagrangian model simulations in backward mode indicate the suppressed long-range transport in the midto lower troposphere and the enhanced southern origin of air masses for all tropospheric levels during the heat wave. Ozone and carbon monoxide also present strong anomalies (both ∼+40 ppbv) during the heat wave, with a maximum vertical extension reaching 6 km altitude around 11 August 2003. Pollution in the planetary boundary layer (PBL) is enhanced during the day, with ozone mixing ratios two times higher than climatological values. This is due to a combination of factors, such as high temperature and radiation, stagnation of air masses and weak dry deposition, which favour the accumulation of ozone precursors and the build-up of ozone. A negligible role of a stratospheric-origin ozone tracer has been found for the lower troposphere in this study. From 29 July to 15 August 2003 forest fires burnt around 0.3×106 ha in Portugal and added to atmospheric pollution in Europe. Layers with enhanced CO and NO y mixing ratios, advected from Portugal, were crossed by the MOZAIC aircraft in the free troposphere over Frankfurt. A series of forward and backward Lagrangian model simulations have been performed to investigate the origin of anomalies durCorrespondence to: M. Tressol (marc.tressol@aero.obs-mip.fr) ing the whole heat wave. European anthropogenic emissions present the strongest contribution to the measured CO levels in the lower troposphere (near 30%). This source is followed by Portuguese forest fires which affect the lower troposphere after 6 August 2003 and even the PBL around 10 August 2003. The averaged biomass burning contribution reaches 35% during the affected period. Anthropogenic CO of North American origin only marginally influences CO levels over Europe during that period.

New Insights on the Chemical Composition of the Siberian Air Shed From The Yak-Aerosib Aircraft Campaigns

There are very few large-scale observations of the chemical composition of the Siberian airshed. The Airborne Extensive Regional Observations in Siberia (YAKAEROSIB) French–Russian research program aims to fill this gap by collecting repeated aircraft high-precision measurements of the vertical distribution of CO2, CO, O3, and aerosol size distribution in the Siberian troposphere on a transect of 4,000 km during campaigns lasting approximately one week. This manuscript gives an overview of the results from five campaigns executed in April 2006, September 2006, August 2007, and early and late July 2008. The dense set of CO2 vertical profiles, consisting of some 50 profiles in each campaign, is shown to constrain large-scale models of CO2 synoptic transport, in particular frontal transport processes. The observed seasonal cycle of CO2 in altitude reduces uncertainty on the seasonal covariance between vegetation fluxes and vertical mixing, known as the “seasonal rectifier effect.” Regarding carbon dioxide, w...

Seasonal and interannual variability of carbon monoxide based on MOZAIC observations, MACC reanalysis, and model simulations over an urban site in India

The spatial and temporal variations of carbon monoxide (CO) are analyzed over a tropical urban site, Hyderabad (17°27′N, 78°28′E) in central India. We have used vertical profiles from the Measurement of ozone and water vapor by Airbus in-service aircraft (MOZAIC) aircraft observations, Monitoring Atmospheric Composition and Climate (MACC) reanalysis, and two chemical transport model simulations (Model for Ozone And Related Tracers (MOZART) and MRI global Chemistry Climate Model (MRI-CCM2)) for the years 2006–2008. In the lower troposphere, the CO mixing ratio showed strong seasonality, with higher levels (>300 ppbv) during the winter and premonsoon seasons associated with a stable anticyclonic circulation, while lower CO values (up to 100 ppbv) were observed in the monsoon season. In the planetary boundary layer (PBL), the seasonal distribution of CO shows the impact of both local meteorology and emissions. While the PBL CO is predominantly influenced by strong winds, bringing regional background air from marine and biomass burning regions, under calm conditions CO levels are elevated by local emissions. On the other hand, in the free troposphere, seasonal variation reflects the impact of long-range transport associated with the Intertropical Convergence Zone and biomass burning. The interannual variations were mainly due to transition from El Nino to La Nina conditions. The overall modified normalized mean biases (normalization based on the observed and model mean values) with respect to the observed CO profiles were lower for the MACC reanalysis than the MOZART and MRI-CCM2 models. The CO in the PBL region was consistently underestimated by MACC reanalysis during all the seasons, while MOZART and MRI-CCM2 show both positive and negative biases depending on the season.

Lightning NO x influence on large-scale NO y and O 3 plumes observed over the northern mid-latitudes

This paper describes the NOy plumes originating from lightning emissions based on 4 yr (2001–2005) of MOZAIC measurements in the upper troposphere of the northern mid-latitudes, together with ground- and space-based observations of lightning flashes and clouds. This analysis is primarily for the North Atlantic region where the MOZAIC flights are the most frequent and for which the measurements are well representative in space and time. The study investigates the influence of lightning NOx (LNOx) emissions on large-scale (300–2000 km) plumes (LSPs) of NOy. One hundred and twenty seven LSPs (6% of the total MOZAIC NOy dataset) have been attributed to LNOx emissions. Most of these LSPs were recorded over North America and the Atlantic mainly in spring and summer during the maximum lightning activity occurrence. The majority of the LSPs (74%) is related to warm conveyor belts and extra-tropical cyclones originating from North America and entering the intercontinental transport pathway between North America and Europe, leading to a negative (positive) west to east NOy (O3) zonal gradient with −0.4 (+18) ppbv difference during spring and −0.6 (+14) ppbv difference in summer. The NOy zonal gradient can correspond to the mixing of the plume with the background air. On the other hand, the O3 gradient is associated with both mixing of background air and with photochemical production during transport. Such transatlantic LSPs may have a potential impact on the European pollution. The remaining sampled LSPs are related to mesoscale convection over Western Europe and the Mediterranean Sea (18%) and to tropical convection (8%).

On the representation of IAGOS/MOZAIC vertical profiles in chemical transport models: contribution of different error sources in the example of carbon monoxide

Utilising a fleet of commercial airliners, MOZAIC/IAGOS provides atmospheric composition data on a regular basis that are widely used for modelling applications. Due to the specific operational context of the platforms, such observations are collected close to international airports and hence in an environment characterised by high anthropogenic emissions. This provides opportunities for assessing emission inventories of major metropolitan areas around the world, but also challenges in representing the observations in typical chemical transport models. We assess here the contribution of different sources of error to overall model–data mismatch using the example of MOZAIC/IAGOS carbon monoxide (CO) profiles collected over the European regional domain in a time window of 5 yr (2006–2011). The different sources of error addressed in the present study are: 1) mismatch in modelled and observed mixed layer height; 2) bias in emission fluxes and 3) spatial representation error (related to unresolved spatial variations in emissions). The modelling framework combines a regional Lagrangian transport model (STILT) with EDGARv4.3 emission inventory and lateral boundary conditions from the MACC reanalysis. The representation error was derived by coupling STILT with emission fluxes aggregated to different spatial resolutions. We also use the MACC reanalysis to assess uncertainty related to uncertainty sources 2) and 3). We treat the random and the bias components of the uncertainty separately and found that 1) and 3) have a comparable impact on the random component for both models, while 2) is far less important. On the other hand, the bias component shows comparable impacts from each source of uncertainty, despite both models being affected by a low bias of a factor of 2–2.5 in the emission fluxes. In addition, we suggested methods to correct for biases in emission fluxes and in mixing heights. Lastly, the evaluation of the spatial representation error against model–data mismatch between MOZAIC/IAGOS observations and the MACC reanalysis revealed that the representation error accounts for roughly 15–20% of the model–data mismatch uncertainty.

The first regular measurements of ozone, carbon monoxide and water vapour in the Pacific UTLS by IAGOS

We present the features seen in the first 2 months (July and August 2012) of data collected over the Pacific by IAGOS (In-service Aircraft for a Global Observing System)-equipped aircraft. IAGOS is the continuation and development of the well-known MOZAIC (Measurement of Ozone and Water Vapour on Airbus in-service Aircraft) project where scientific instruments were carried on commercially operated A340 aircraft to make measurements of chemical species in the atmosphere. Here, we show data from an aircraft operated by China Airlines on routes from Taipei to Vancouver, which provided the first trans-Pacific measurements by an IAGOS-equipped aircraft. We describe the chemical composition of the extratropical upper troposphere/lower stratosphere (Ex-UTLS) across the Pacific basin in the Northern Hemisphere. The observed concentrations of ozone span a range from 18 to 500 ppbv indicating sources in the marine boundary layer and lowermost stratosphere, respectively. Concentrations of carbon monoxide (CO) greater than 400 ppbv are observed in the Ex-UTLS suggesting that plumes of pollution have been exported from the continent. These low concentrations of ozone and high concentrations of CO were rarely recorded in 8 yr of MOZAIC observations over the Atlantic.