Particle remobilization in urban systems

Aeroallergens, such as those derived from pollen grains, are known to trigger asthma epidemics. Outbreaks are highly seasonal and their frequency increases in summer. During prolonged urban heat wave, a significant portion of the pollen deposits on urban surfaces. Extreme urban winds then cause pollen remobilization, that rapidly spreads within cities. The remobilization of micron-sized aeroallergens from urban surfaces by strong winds has received scare attention. In this work, the simulation of particle remobilization and subsequent propagation for some selected cities in Germany is performed. Simulations will be used to locate urban zones subject to high pollen concentrations. These geographical urban data will contribute to development of mobile applications. Further preventing measures, such as targeted pavement watering and optimized tree location in cities, will also be suggested to limit asthma epidemics during extreme events.

Pollen particles are almost spheroidal in shape, with an equivalent diameter normally ranging from about 10 to 50 µm. Experiments performed in wind tunnels allow for the development of particle remobilization models. For simulating the propagation of the re-mobilized material in urban systems, the lattice Boltzmann method is employed. It has several advantages over the classical Eulerian/Navier-Stokes solvers. It benefits from a straightforward implementation and does not need a pressure correction. The locality of the operators allows taking full advantage of recent advances in parallel General Purpose Graphical Processing Units (GPGPU) for fast calculation. A two-way coupling between the continuous air and dispersed particulate phases has been used for simulating particle remobilization and propagation.

Funding

This work is funded by the Helmholtz Associations Initiative and Networking Fund within the frame of the Helmholtz Climate Initiative (HI-CAM / Adaptation)

References

• Banari, A., Henry, C., Eidt, R.H.F, Lorenz, P., Zimmer, K., Hampel, U., Lecrivain, G., Evidence of collision-induced resuspension of microscopic particles from a monolayer deposits, Physical Review Fluids, Under Review, 2021
• Banari, A., Mauzole, Y., Hara, T., Grilli, S.T., Janßen, C.F., The simulation of turbulent particle‐laden channel flow by the Lattice Boltzmann method, International Journal for Numerical Methods in Fluids 79, 10, 491-513 (2015)