Urban Air Pollution Canyon: Street Vortex & Pollutant Trapping (2D)

This 2D companion reduces the 3D street canyon to the cross-section that actually explains it: a closed-form single-cell vortex stream function whose closure strength depends on the building-height-to-street-width aspect ratio, tracer particles emitted at street level standing in for traffic, and a live heatmap plus wall-concentration strip chart that show pollutant physically piling up against the upwind building's leeward wall while the downwind windward wall stays comparatively clean — the real, well-documented street-canyon asymmetry, driven by adjustable wind speed, geometry and emission rate rather than decorative haze.