Driving pollution upwards

It might be possible to reduce urban pollution by using suspended polythene chimneys in which air would rise because of a confined greenhouse effect, and be replaced by air being sucked in at the bottom, thus discharging polluted air up high.

This idea touches on some real atmospheric physics. The core concept is physically sound in principle. A transparent enclosure heating air to create an upward convective column, essentially a solar chimney, is a well-established idea. The ‘Solar Updraft Tower’ concept has been studied seriously for electricity generation since the 1970s.

Sunlight passing through polythene would heat the enclosed air, reducing its density and causing it to rise. This would create a pressure differential drawing in air at the base. Pollutants carried in that air would be borne upward and released at altitude, where dispersion is far better. The taller the chimney, the stronger the updraft (the physics strongly favour height)

The significant challenges include energy balance. The greenhouse heating effect in a thin polythene tube is modest. The temperature differential drives the flow, but in a narrow column heat is lost through the walls quickly, limiting the effect. To meaningfully process city-scale air, huge throughput would be needed. This would mean many large chimneys, or very wide ones

Wind interference would have to be dealt with. Tall, lightweight polythene structures could be severely disrupted by crosswinds, which would also collapse the thermal column.

And pollution is being moved, not removed. The pollutants still enter the atmosphere, just higher up. The advantage would be in the location of the pollution, not its total quantity.

Structural engineering - keeping a tall polythene tube taut, stable, and optically useful in an urban environment poses serious materials and engineering problems, but more promising variants of this idea that have been explored:

Solid solar updraft towers (Manzanares prototype, Spain, 1982) used solar chimneys for natural ventilation and power generation. Tall industrial stacks already exploit exactly this principle thermally

While it would not remove pollution from the ecosystem, it could genuinely improve ground-level air quality by accelerating vertical dispersion, which is actually how tall industrial chimneys have worked for over a century.

The polythene greenhouse twist is the novel part, though solar gain through polythene may be too modest to drive a useful flow without supplemental heating. This is the kind of idea worth modelling computationally; the fluid dynamics are tractable and someone could calculate whether realistic solar gain through polythene produces sufficient updraft velocity for meaningful air throughput. It might be worth testing.

Madsen Pirie