When is dispersion modelling required rather than optional?+
It is normally required where an activity has significant point-source emissions and an assessment must demonstrate compliance with ambient standards at sensitive receptors, which in practice covers most industrial environmental impact assessments. It also becomes necessary when a regulator, lender or reviewer challenges the adequacy of proposed stack parameters, when several sources combine on one site, or when an existing facility needs to justify its operating envelope after a complaint.
Which models do you use and why does the choice matter?+
Model selection follows the problem: steady-state Gaussian models are appropriate for most near-field industrial sources over moderate terrain, while puff or advanced models suit long range transport, calm conditions, complex terrain or coastal recirculation. Microclimate and wind studies use computational fluid dynamics or dedicated urban climate tools. The choice is defensible only when it is justified against the physical situation, and we document that justification in the report.
What happens if good meteorological data is not available?+
This is a common constraint in Egypt. Options include using the nearest representative station with a documented justification, using prognostic meteorological data, or commissioning site measurement where the assessment is high stakes. Whichever route is taken, the limitation must be stated and its effect tested through sensitivity analysis. A model run on unrepresentative meteorology can be confidently wrong, which is worse than being openly uncertain.
How accurate are the predicted concentrations?+
Dispersion models predict statistical patterns rather than specific hours, and their accuracy depends far more on input quality than on the model itself. Emission rates and meteorology dominate the uncertainty. Regulatory practice manages this through conservative assumptions and comparison against percentile metrics rather than single values. We report results with their basis and limitations stated, and we test sensitivity to the inputs most likely to change the conclusion.
Can modelling be used to reduce mitigation cost?+
Often, yes. Modelling frequently shows that an intuitive mitigation choice is not the binding constraint. Raising a stack, relocating a source, changing exit velocity, adjusting operating hours or repositioning a building can achieve compliance at a fraction of the cost of abatement equipment. The value of modelling early is exactly this: it tests options while they are still cheap to change, rather than confirming a decision that has already been procured.
What is microclimate modelling used for?+
It assesses how a masterplan or building layout affects outdoor thermal comfort, wind conditions at pedestrian level, shading and natural ventilation. In a hot climate this is a design tool rather than a compliance exercise: it informs orientation, spacing, massing, shading, surface materials and planting. Tested early, it improves usability of outdoor space and reduces cooling demand; tested late, it can only document what has already been built.
How do you handle cumulative impact from neighbouring facilities?+
Cumulative assessment requires background concentrations and, where relevant, explicit modelling of nearby sources. Background can come from monitoring data or a defensible published dataset, and neighbouring industrial sources may need to be modelled where their emissions are significant and their parameters are obtainable. The report should always separate project contribution from background, because mitigation decisions differ depending on which one drives the exceedance.
