Thèse de la Pollution Atmosphérique à l'Exposition des Écosystèmes Retracer les Dépôts de Poussières Sahariennes et de Contaminants le Long d'Un Gradient Urbain-Montagne et dans les Archives Tourb H/F Doctorat.Gouv.Fr

Établissement : Institut National Polytechnique de Toulouse École doctorale : SDU2E - Sciences de l'Univers, de l'Environnement et de l'Espace Laboratoire de recherche : CRBE - Centre de Recherche sur la Biodiversité et l'Environnement Direction de la thèse : Gaël LE ROUX ORCID 0000000215790178 Début de la thèse : 2027-09-01 Date limite de candidature : 2026-11-23T23:59:59 La pollution atmosphérique est généralement évaluée à partir des concentrations de particules dans l'air, alors que leur dépôt, qui constitue le transfert effectif des particules et des contaminants associés vers les écosystèmes terrestres, reste beaucoup moins bien contraint. Ce projet de thèse vise à relier observations atmosphériques contemporaines, dépôts, archives environnementales et réponses des écosystèmes afin de mieux comprendre l'exposition des milieux pyrénéens aux poussières sahariennes et aux contaminants.

Le projet s'appuiera sur un gradient d'observation allant de Toulouse, environnement urbain soumis à de fortes émissions anthropiques, à Auradé, site agricole, puis à Bernadouze, site montagnard forestier et tourbeux exposé au transport atmosphérique à longue distance. Les mesures de dépôts seront confrontées aux concentrations de particules atmosphériques, aux données météorologiques, aux observations satellitaires, aux rétrotrajectoires de masses d'air et aux modèles régionaux de transport des poussières. Cette approche permettra d'identifier et de quantifier les épisodes de poussières sahariennes, d'évaluer leur dépôt effectif et de les distinguer des sources locales et régionales, notamment la remise en suspension des sols, l'agriculture, le trafic et les émissions de combustion.

La composition élémentaire des aérosols, dépôts, tourbes et végétaux sera caractérisée par ICP-MS, ICP-OES et fluorescence X, complétée par des approches d'imagerie et de spectroscopie des particules. Une attention particulière sera portée aux métaux traces et aux contaminants émergents, notamment les microplastiques atmosphériques, afin d'étudier leur co-transport et leur dépôt avec les particules minérales. Des traceurs géochimiques, rapports élémentaires, facteurs d'enrichissement et approches statistiques multivariées permettront d'attribuer les principales sources et de suivre leur variabilité au cours des événements de pollution.

La dimension contemporaine sera prolongée par l'étude d'archives tourbeuses ombrotrophes pyrénéennes, qui enregistrent les dépôts atmosphériques sur des échelles allant de plusieurs siècles à plusieurs millénaires. Les flux de poussières minérales et de contaminants seront reconstruits à partir de la teneur en cendres, des éléments lithogènes, des terres rares, de la granulométrie et de marqueurs de pollution, sur des chronologies établies notamment par radiocarbone et radionucléides à courte période. La comparaison avec les observations actuelles permettra de replacer les changements récents dans une perspective de long terme et d'évaluer si l'intensification récente des apports sahariens et anthropiques est exceptionnelle.

Enfin, le projet examinera l'interception, la rétention et le transfert potentiel des poussières, nutriments et contaminants par la végétation forestière et les zones humides. Il établira ainsi un continuum original entre pollution atmosphérique, dépôt réel, exposition des écosystèmes et archives environnementales. Inscrit dans la collaboration franco-espagnole ECOAIR et co-encadré avec l'IPE-CSIC, il contribuera au développement de nouveaux indicateurs utiles à la surveillance de la qualité de l'air, des écosystèmes de montagne et des changements environnementaux. Air pollution is one of the leading environmental threats to human health, contributing to an estimated 6.7 million premature deaths worldwide each year(Types of pollutants, n.d.). The challenge is particularly acute in southern Europe, where urban emissions, heatwaves and intense Saharan dust intrusions can occur simultaneously (La canicule de juin 2026 dopée aux aérosols sahariens CNRS Terre & Univers, 2026). These compound events may sharply increase PM. and PM concentrations and exacerbate cardiovascular and respiratory risks .

Recent research has revealed increasing dust concentrations across much of Europe. A continent-wide study combining atmospheric measurements, modelling and an Alpine ice-core record reported increasing background dust concentrations and more severe dust intrusions during the past decade, together with an approximately 110% increase relative to pre-industrial levels in the Alpine record (Vasilakos et al., 2026). These results suggest that European dust exposure is being reshaped by both North African desertification and changes in atmospheric circulation.

Saharan dust has consequences extending far beyond air quality. It transports mineral particles, nutrients, microorganisms and anthropogenic contaminants over thousands of kilometres. Its deposition may fertilise nutrient-poor terrestrial and aquatic ecosystems , while dust deposited on snow reduces surface albedo and can accelerate snowmelt. However, the ecological consequences of these inputs depend not only on the atmospheric particle load but also on the quantity, composition and bioavailability of the material deposited.

Emerging contaminants including microplastics add a new dimension to this issue. These persistent particles can undergo long-range atmospheric transport and are now detected in urban, rural and remote environments. Together with emerging trace metals and other anthropogenic substances, they belong to the wider category of novel entities, for which the planetary boundary is considered to have been exceeded (Richardson et al., 2023). Nevertheless, their co-transfer with mineral dust and their deposition onto terrestrial vegetation remain poorly understood.

The project will build on the ongoing collaboration between Jorge Pey (IPE CSIC, Spain) and Gaël Le Roux (CNRS, CRBE Univ Toulouse) within ECOAIR, a major European POCTEFA project (P.I. Pr. Miguel Escudero) investigating air pollution across the Pyrenean cross-border territory. The PhD will consolidate this research effort while introducing an innovative focus on deposition records from the Toulouse, Auradé and Bernadouze observatories. By combining these contemporary records with peat archives, the project will establish a temporal continuum extending from individual pollution events to environmental changes over centuries and millennia.
The project directly addresses the TIRIS Toulouse University pillars Health and Well-being and Global Changes and Impacts, while also contributing to Sustainable Transitions through the development of improved environmental indicators and evidence supporting air-quality and ecosystem-management policies.
Air pollution and mineral dust are generally investigated through atmospheric concentrations, whereas their deposition-the actual transfer of particles and associated contaminants to terrestrial ecosystems-remains much less well constrained. This PhD project will bridge this gap by connecting present-day atmospheric observations with deposition monitoring, long-term environmental archives and ecological responses.

Its main objectives are to:
1. Identify and quantify Saharan dust events and distinguish them from local and regional anthropogenic sources using elemental composition, geochemical tracers, atmospheric observations and transport models.
2. Investigate the co-transport and deposition of trace metals and emerging contaminants, particularly atmospheric microplastics.
3. Reconstruct long-term variations in Saharan dust and atmospheric pollution over the past centuries to millennia using ombrotrophic peat archives.
4. Assess the effects of mineral dust, nutrients and associated contaminants on forest and wetland vegetation.
5. Connect short-term atmospheric processes with long-term environmental change and provide new indicators relevant to air-quality assessment, ecosystem monitoring and environmental policy
The project will use an interdisciplinary approach combining atmospheric monitoring, environmental geochemistry, particle characterisation, palaeoenvironmental reconstruction, ecological observations and statistical modelling.

1. Contemporary atmospheric monitoring and deposition

Atmospheric particulate matter and deposition samples are collected from contrasting observatories, including urban Toulouse, the agricultural site of Auradé and the mountain wetland and forest environment of Bernadouze. These sites provide a unique gradient from major anthropogenic emission sources to rural and mountain environments exposed to long-range atmospheric transport.
The deposition records will be compared with available atmospheric PM measurements, meteorological observations, satellite products, air-mass back trajectories and regional dust-transport models. This will make it possible to identify Saharan dust intrusions and determine how efficiently atmospheric particles are transferred to terrestrial surfaces.


2. Geochemical and particle characterization

The elemental composition of aerosols, deposition samples, peat and vegetation will be determined using complementary analytical techniques including ICP-MS, ICP-OES andX-ray fluorescence. Lithogenic tracers will be used to identify mineral dust, while trace metals will provide information on anthropogenic contamination and mixing between natural and human-derived sources.
Particle imaging and spectroscopic methods will be used to characterise particle size, morphology and composition. Atmospheric microplastics will be identified and quantified using suitable microscopic and spectroscopic approaches (Raman, FTI-IR, Colspec), depending on particle size and sample matrix.

3. Source attribution and event reconstruction

Geochemical fingerprints will be combined with atmospheric transport information to distinguish Saharan dust from local soil resuspension, agricultural emissions, traffic, combustion and other urban sources. Multivariate statistics, enrichment factors, elemental ratios and source-apportionment approaches will be applied to identify the principal particle sources and their temporal variability.
High-resolution event monitoring will allow individual Saharan dust and pollution episodes to be investigated, including interactions between mineral dust, trace metals and microplastics.

4. Long-term reconstruction from peat archives

Ombrotrophic peatlands receive water and particles predominantly from the atmosphere and therefore constitute valuable archives of past atmospheric deposition (Le Roux et al., 2012). Peat cores will be selected from suitable Pyrenean sites from Toulouse peat library and investigated at high temporal resolution.
Chronologies will be developed using radiocarbon and, where appropriate, short-lived radionuclides such as ²¹Pb and ¹³Cs. Mineral dust accumulation will be reconstructed using ash content, lithogenic elements, rare earth element patterns, particle-size measurements and complementary microscopic observations. Trace metals and microplastics will be investigated to reconstruct the development of anthropogenic atmospheric contamination.
Comparison between peat records and the approximately ten-year atmospheric monitoring record will enable recent observations to be placed within their longer-term environmental context.

5. Ecological effects on vegetation

The project will examine the interception and retention of deposited particles by forest and wetland vegetation. Differences among plant functional groups and environmental settings will be investigated using vegetation, surface-deposition and, where appropriate, soil or peat samples.
Elemental and particle analyses will be used to assess whether vegetation acts primarily as a passive collector or whether deposited mineral nutrients and contaminants are transferred into plant tissues. This component will provide an initial assessment of the ecological consequences of Saharan dust and contaminant deposition in mountain forests and wetlands.