air quality assessment & management
Reference and User Manual
AirWare   On-line Reference Manual
  Release Level 7.0
  Revision Level beta
  Release Date 2015 03

Computational kernel

The high-resolution near field dispersion model for line sources (traffic) used is based on AERMOD, and uses a computational kernel based on an area source (Gaussian solution with an hourly aggregation period) with a mixing zone approach in and over the street itself with unit emissions. The mixing zone approach represents the high turbulence over and near the street itself, due to
  • the energy budget (heating) of a sealed street surfaces and resulting vertical turbulence;
  • the turbulent mixing caused by the moving traffic itself.

The kernel results are then scaled according to actual traffic frequency, speed, and fleet composition, and distributed along the line sources by a convolution method.

The kernel is defined in terms of its resolution (default: 10m) and size (1-5 km), and the mixing zone parameters, expressed as a set of symbolic choices of algorithms.
The kernel is linked to

  1. individual line sources, where the model is run for a single hour;

  2. AERMOD scenarios, where the traffic part is computed with the convolution method based on the kernel, which is generated for 24 subsequent hours for a complete AERMOD 24 hour scenario.

In the latter case, the 24 kernel solution are using the actual hourly meteorological data, and the results can be viewed under an animation tape deck control.

Kernel tuning

To represent the turbulent mixing close to the source (street) due to the movement of vehicles, the kernel can be "tuned" with the application of a low-pass filter; the user defines the size of the "mixing zone" as well as the number of passes used to redistribute concentration (mass conservative) in the mixing zone.

The compairson of original and modified kernal shows the reduction of the original concentration maxima close to the source in the "middle of the street".

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