Nico Schulte

Dispersion of buoyant emissions from low level sources in urban areas: water channel modelling

A laboratory study was done to investigate dispersion of buoyant emissions from near surface sources in urban areas. Ground level concentrations under different surrounding building geometries were measured using a newly developed system based on laser induced fluorescence. In the presence of upstream buildings AERMOD (AMS/U.S. EPA regulatory dispersion model) is unable to explain concentrations close to the source. Plume visualisations and velocity measurements show that upstream buildings induce low velocity and a highly turbulent region near the stack, which increases the plume rise and induces rapid vertical mixing. Also, the urban canopy imposes a length scale on the horizontal turbulence, causing the plume to spread laterally with the square root of distance (~x1/2) rather than linearly as occurs in open terrain. A Gaussian-based dispersion model which accounts for these effects performs substantially better in predicting ground level concentrations associated with buoyant emissions from distributed power generators in urban areas.

On formulating equations for plume spreads for near-surface releases

Recent concerns about effects of automobile emissions on the health of people living close to roads have motivated an examination of models to estimate dispersion in the surface boundary layer. This examination led to new formulations for horizontal and vertical plume spread described in Venkatram et al. (2013). Concentration estimates based on the proposed plume spread equations compare well with data from both the Prairie Grass experiment (Barad, 1958) as well as the recently conducted Idaho Falls experiment (Finn et al., 2010). This paper describes a simpler approach to deriving the new equations proposed in the earlier paper.