Scientific questions

Surface processes and atmospheric dynamics. Understand the connections and interactions between surface processes in heterogeneous urban environments, spatio-temporal dynamics of the atmospheric boundary layer (ABL), local meteorological phenomena (eg heat waves, development of cloud layers, thunderstorms) and local circulations induced by the city that impact heat and pollution.
The following scientific questions are formulated in the framework of the H2C project:

  • how does the city (roughness of buildings, heat) influence the processes of atmospheric transport and the spatio-temporal evolution of the ABL?
  • what determines the exchange of air between contrasting areas (residential areas and parks, city and countryside)?
  • to what extent do the heterogeneous urban and rural surfaces that surround them generate contrasting energy balances on the surface?
  • how to exploit ventilation routes to improve the transport of fresh air to urban hotspots?
  • how to improve surface roughness parameterizations in urban areas.

Atmospheric composition and chemistry. Analyze the atmospheric chemical composition in the Paris region in order to better understand its sources, its physico-chemical transformations (in particular when anthropogenic emissions mix with urban biogenic emissions but also with those of the surrounding forests), its interactions with the regional climate, and its impact on air quality.

The ACROSS project seeks to answer the following scientific questions:
How do VOC oxidation pathways change when urban and biogenic air masses mix?
How are the balances of oxidants and reactive nitrogen compounds affected by the mixing of biogenic and urban air masses, day and night?
How are the formation and aging of aerosols, their properties particularly linked to the organic carbon content, modified when urban and biogenic air masses mix?
What are the consequences of these factors for air quality, for the health of the biosphere and for the representation of these processes in numerical models?

The STREET project focuses on scientific questions:
What are the precursors of organic aerosols whose high concentrations are observed in urban areas? How is the formation of organic aerosols in the city influenced by the interactions between different emission sources?
What is the impact of urban trees on air quality? They can be sources and sinks for local pollution. Do their emissions of volatile organic compounds influence urban organic aerosols?

Numerical simulations. Improve very high resolution (100 m) atmospheric models for forecasting (1) environmental conditions in cities thanks to a database of observations making it possible to qualify the variability of the urban climate on a scale comparable to the fine mesh of the models, (2) local urban concentrations to which the population is exposed (which are higher than background urban concentrations).
This leads to the following scientific questions:
– What physical improvements are needed in the models (e.g. are energy budgets correctly measured and represented in weather and climate prediction models.)?
– Are the exchanges between the regional and local scales well represented in the models?
– Is urban climate variability well simulated?
– What observation networks are needed in the urban environment, and how to exploit opportunity measures?
– What are the relevant indicators for urban users?