[EN] The objective of the YAK-AEROSIB project is to establish systematic observations of atmospheric concentrations in CO₂, CH₄, CO, O₃ and aerosols over the interior of Eurasia. Those measurements will be collected during several years onboard of a research airplane, over a transcontinental route between Western and Eastern Siberia. Observations of CO₂ and CO gradients in the lower and middle troposphere will serve to infer the sources of those gases due to anthropogenic activities and biomass burning, using inverse modelling techniques. Observations of O₃ and CO₂ interpreted with chemistry-transport models will serve to quantify the chemical and dynamical processes which yield to the formation and long range transport of O₃ in the Northern Hemisphere.

[FR] L’objectif du projet YAK-AEROSIB est d’établir des observations systématiques des concentrations atmosphériques de CO₂, de CH₄, de CO, d’O₃ et d’aérosols en Eurasie. Ces mesures seront recueillies pendant plusieurs années à bord d’un avion de recherche, sur une route transcontinentale entre la Sibérie occidentale et orientale. Les observations des gradients de CO₂ et de CO dans la troposphère inférieure et moyenne serviront à déduire les sources de ces gaz dues aux activités anthropiques et à la combustion de la biomasse, en utilisant des techniques de modélisation inverse. Les observations d’O₃ et de CO₂ interprétées à l’aide de modèles de chimie-transport serviront à quantifier les processus chimiques et dynamiques qui aboutissent à la formation et au transport à grande distance d’O₃ dans l’hémisphère nord.

There are very few large scale observations of the chemical composition of the Siberian air shed. More observations as well as further data analysis are needed to improve global climate models including representations of aerosol and gas phase chemistry and biogeochemical cycles. Transport, transformation and emission assessment are expected to be improved by new observations. Validation of satellite measurements of the atmospheric composition is another goal as space observations are extensively used for the Arctic monitoring. The Airborne Extensive Regional Observations in Siberia (YAK-AEROSIB) French-Russian project aims to fill this gap by performing new aircraft high-precision measurements of the vertical distribution of CO₂, CH₄, CO, O₃ and aerosol in the Siberian troposphere on transects of more than 8000 km, and by analyzing new and existing datasets. This projects builds upon the successful YAK-AEROSIB GDRE project (2003-2010).

YAK-Aerosib aircraft Antonov 30 (photo G. Athier)

Very few measurement programmes exist over Siberia to document the tropospheric composition (Crutzen et al., 1998; Ramonet et al., 2002; Paris et al., 2008; Sasakawa et al., 2010; Kozlova et al., 2008). Therefore, large uncertainties currently surround our knowledge about biogeochemistry and the distributions/emissions of compounds important for tropospheric chemistry and climate change. Relevant species that require further measurements include CO₂ and CH₄ for biogeochemical cycles, and CO, O₃, and aerosols including black carbon for tropospheric composition. Other tracers need further investigation, including stable isotopic composition of CO₂ and CH₄ for the attribution of sources and sinks of these species in the considered area.

With a large fraction of forest surface area (800×106 ha) and its huge stocks of carbon (~320 GtC), Siberia is a significant player of the global carbon budget. Potential for managed carbon storage in ecosystems exist (Kurganova et al., 2010). Permafrost, a dominant feature of Siberian landscapes, stores ~1672 GtC (Tarnocai et al., 2009). But its ecosystems are vulnerable to global climate change through modification of the balance between Net Primary Production and respiration in a warmer climate, release of carbon by permafrost melting and an increase in wildfires. Siberian forests are currently assumed to be a sink, although with a large uncertainty (range 0-1 PgC yr^-1; Gurney et al., 2002) due to data scarcity for atmospheric inversions. Atmospheric inversions infer surface fluxes from measured atmospheric CO₂ concentration gradients using atmospheric tracer transport models. But the scarcity of observations and unknown biases in tracer transport models affect CO₂ inversions (‘rectifier effect’, Denning et al., 1999). Siberia, with its large forested area and highly seasonal CO₂ flux and transport, is a ‘hot-spot’ of CO₂ transport model uncertainties (Gurney et al. 2002) which can be approached using aircraft measurements (Stephens et al., 2007).

Methane (CH₄) is newly measured through the YAK AEROSIB campaigns [ link ]. CH₄ is the second most important anthropogenic greenhouse gas. It is also emitted by a number of natural processes, including wetlands and permafrost degradation. Its main sink being oxidation in the troposphere against OH, it is also exerting a strong control on atmospheric chemistry. The sources and sinks of CH₄. Rigby et al. (2008) reported a renewed increased of CH₄, after several years of stable concentration, but attribution for these variations remain unclear.

High latitude biomes influence the global methane budget (Bousquet et al., 2006) in several ways, including wetlands emissions, reactivation of bacterial activity through permafrost melting (Zimov et al., 2006), thermokarst lakes bubbling (Walter et al., 2006) and potential destabilization of methane hydrates in coastal permafrost. In a warming climate, these altered processes are expected to feed back into the global radiative forcing and hence further enhance climate change. Our current understanding of the extent and amplitude of these sources, as well as the large scale driving factors, remain highly uncertain (Bloom et al., 2010). Anthropogenic emissions of CH₄ from leakages of natural gas pipelines are also not well quantified. In addition, as northern regions of Russia warm there is likely to be additional exploitation of natural gas reserves. As a result and due to the lack of regional observations, it can only be conjectured from zonal gradients that the recently resumed increase in global atmospheric CH₄ concentrations was initiated by unusually high temperature at high northern latitudes in 2007 (Dlugokencky et al., 2009). Currently, Siberian wetlands are a large source of CH₄ (see Fig.).

Fig. Wetland July CH₄ fluxes in 2000-2005, from CarboScope [ link ], after Bousquet et al. (2006). This flux map is obtained by inverse modelling of discrete sampling monthly means at 68 locations around the world. None of these stations is located in Siberia.

Atmospheric pollutants released by human activities in mid-latitude industrialized regions of the Northern Hemisphere are quickly moved over long distances by atmospheric transport. Intercontinental pollution transport has become of increasing concern because of its effect on local and regional air quality levels. The main pollution transport pathways differ qualitatively between North Asia (including Siberia), Western Europe and North America. Model simulations show that European pollutants are predominantly dispersed eastwards over Siberia in summer, or North-eastwards towards Siberia and the Artic in winter (Stohl and Eckhardt, 2004, Wild et al., 2004; Duncan and Bey, 2004). Emissions from Europe remain mostly below 3000 m during transport eastwards and model studies undertaken as part of the Task Force on Hemispheric Transport of Atmospheric Pollutants (TF-HTAP), under the auspices of the Convention on Long-Range Transport of Air pollutants (CLRTAP) have shown that European pollution is a major contributor to background pollutant levels over Asia (e.g. Fiore et al., 2009). Whilst pollutant export from North America and Asia have been characterised by intensive field campaigns (Fehsenfeld et al., 2006; Singh et al., 2008 for INTEX-B), the export and long-range transport of European pollution across Siberia has received very little attention. Satellite provide information about spatial distributions but often retrievals have low sensiitvity in the lower troposphere (Pommier et al., 2010) making validation against in-situ observations imperative. In addition, emissions from forest fires (van der Werf et al., 2006) and by prescribed agricultural fires in Southern Siberia, Kazakhstan and Ukraine (Korontzi et al. 2006) in spring and summer are large sources of trace gases such as CO (Nédélec et al., 2005) and aerosols which can have a significant impact on the chemical composition over Siberia, and more generally the CO budget of the NH (Wotawa et al., 2001). They also vary greatly from year to year. These pollutants can also be transported to the Arctic (Warneke et al., 2009) where they can influence the radiative budget. Deposition of absorbing black carbon aerosols on snow may also impact snowmelt and sea-ice melt in the Arctic.

Six campaigns and a test flight have been performed over the period 2006-2010. Organising these campaigns required important scientific, technical and administrative achievements, including the development of new instruments or adaptation of existing ones, testing the instruments in the laboratory and during the test flight, defining the sampling strategy and obtaining clearances for flight over the Russian territory.

The YAK-AEROSIB partners have been active during the International Polar Year with the participation in the POLARCAT international IPY project. Two campaigns have been performed in this context and data were shared with international participants, enhancing the visibility of the project.

Instrumental development has included the adaptation of MOZAIC (in-situ measurement onboard commercial airliner) airborne instruments, development of a new high-precision CO₂ analyser, and the development of an in-situ laser diode isotopic sensor.

The analysis of the data has led to more than 10 scientific papers as of now. Two PhD theses (LSCE, LATMOS) and two Masters theses (LA, LSCE) were dedicated to YAK-AEROSIB. Findings include the long range transport of Chinese pollution toward Siberia and the Arctic (Paris et al., 2008), the underestimation of vertical mixing and the related bias in a model of atmospheric CO₂ used for inversions (Paris et al., 2010), the investigation of new particle formation in deep continental clean troposphere (Arshinov et al., 2008, Paris et al., 2009). Data were also used to validate IASI, a space-borne sensor of atmospheric chemistry, in relation with wildfire plumes in the Arctic (Pommier et al., 2010). The analysis of in-situ airborne trace gas measurements has improved the analysis of aerosol remote sensing data which depends on many factors: transport pathways, interaction of anthropogenic sources, forest fires and desert emissions, deposition and transformation. A novel clustering technique based on simulated atmospheric transport has been developed and applied to YAK-AEROSIB data to disentangle the respective impact of atmospheric mixing and surface emissions on tropospheric composition (Paris et al., 2009). Validation of models is ongoing through collaborations (Tilmes et al., 2011, Feng et al., 2010).

See also: [ link ]

• iCUPE: Integrative and Comprehensive Understanding on Polar Environments. It is a project that answers to ERA-PLANET (European network for observing our changing planet) thematic strand 4 (Polar areas and natural resources).
• PARCS:  the follow up of Polarcat.
• Polarcat (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport), ARCTAS.
• CLIMSLIP (Climate impacts of short-lived pollutants in the polar regions), ANR Blanc project in France
• RAMCES Service d’Observation , ICOS
• COST-PERGAMON WP5
• MOZAIC and IAGOS
• TROICA (train campaigns onboard the Transsiberian)
• IPY-related projects.