STREET

Urban trees emit biogenic volatile organic compounds (BVOCs) that can react with air pollutants to form secondary pollutants, such as ozone (O3) and secondary organic aerosols (SOAs). The objectives of the sTREEt project (Impact of STress on uRban trEEs on ciTy air quality, ANR-19-CE22) are i) to analyse the interactions between urban abiotic factors, the physiology of trees and their VOCB emissions, ii) to model the functioning of the urban tree and iii) to integrate all these data into air quality models. It is based on two experiments and on tree and air quality modelling.
Experiment 1, located in Vitry, France, uses young plane trees (Platanus x hispanica) grown in an urban environment in pots in order to control their water status, the main factor limiting the development of urban trees. The first measurement campaigns in 2020 and 2021 enabled the measurement of VOCB emissions at the leaf and branch level as well as the physiological characterisation of the trees. Experiment 2 (June-July 2022) will use older trees from an urban site. VOC emissions will be measured in situ as well as the composition of the surrounding air in order to assess the impact of VOC emissions on the gaseous and particulate phases.
The experimental data obtained will feed the modelling part of the project. The hydraulic functioning of the urban tree will be modelled as a function of radiative conditions, stomatal regulation and the radial diffusion of water from the soil to the roots. This project will provide a better representation of the parameters required for the parameterisation of VOCB emissions that will be used by the air quality modelling (Polyphemus) that will finalise this study. This model will simulate the concentrations of O3, NOx, PM10, PM2.5 (including organic compounds), at the regional scale and in the streets of Paris, which will be compared to the VOCB emissions measured in situ. This model, useful for city managers, will make it possible to validate the impact of vegetation, stressed or not, on ozone and particle concentrations in Greater Paris.
This project interacts with the ACROSS project for which it represents a secondary urban site during the measurement campaign planned for the summer of 2022