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Reference : UMR7263-KHEBOU-005
Workplace : MARSEILLE 03
Date of publication : Tuesday, October 12, 2021
Scientific Responsible name : email@example.com et firstname.lastname@example.org
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 December 2021
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Mediterranean forest litter as a source of emission of Volatile Organic Compounds (VOCs) in a more arid climate: what consequences for air quality at the regional level?
The thesis will focus on the study of the emissions of Biogenic Volatile Organic Compounds (BVOCs) from soil covered with litter in a Mediterranean forest environment, in order to better understand their contribution to air quality (formation of O3 in particular). This work is multidisciplinary since- it gathers knowledge from ecology, atmospheric chemistry and analytical chemistry- and presents an experimental component and a modeling component which will be modulated according to the profile of the successful candidate.
Biogenic Volatile Organic Compounds (VOCs) are molecules derived from the secondary metabolism of plants and are strongly modulated by environmental conditions (temperature, light, humidity). While BVOC emissions from vegetation contribute to the defense of the plants that produce under biotic stressors (e.g herbivory, parasitism; Dicke et al. 2003) and abiotic stressors (e;g thermal or water stress; Vickers et al. 2009, Possell & Loreto 2013), they also have a major role in the chemistry of the lower atmosphere (the troposphere). Through complex reactions with nitrogen oxides (NOx) - from road transport in particular - and in the presence of light, VOCs participate in the formation of secondary organic aerosols (AOS) and tropospheric ozone which is particularly concentrated in rural areas in the Mediterranean region.
Both, knowledge of BVOC sources and the parameters that drive their variations are therefore essential to improve estimations of air quality on a global scale but also on a regional scale. While BVOC emissions from trees and shrubs have been studied since the 1980s (Guenther et al 1993; Genard-Zielinski et al. 2018), the first studies which targeted BVOCs from litter (i.e. dead leaf biomass deposited in soil) or soil covered by litter as a source of VOCB emissions date from the 2000s and remain rare (Isidorov et al. 2003, Peñuelas et al. 2014, Viros et al. 2020; Viros et al. 2021). These latest studies show that, for a given plant species, the emission rates from the litter can be 5-10 times lower than those from the canopy.
Given that litter is present throughout the year in the forest, the soil covered with litter can therefore be an important source of BVOC and could therefore help to explain the concentrations of secondary pollutants (O3 and AOS) in the PACA Southern region, alike trees and shrubs. However, this biogenic source is currently totally neglected in models used to estimate air quality. In addition, drought intensification and temperature increases predicted in the Mediterranean region under future climate change (Cramer et al. 2018, IPCC 2019) could have an impact on these emissions on a regional scale. While numerous studies have assessed changes of canopy BVOC under the influence of climate change, changes on soil emissions have not yet been explored.
Constraints and risks
The experimental work requires to adapt and modify the campaign dates according to the weather conditions. The candidate will therefore have to adapt to these changes.
The candidate will have to juggle between the academic (IMBE, LCE) and professional (AtmoSud) modes of works, which does not necessarily represent a constraint but requires the ability to adapt to different constraints.
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