How do I remove powdery haze from aluminum siding?

Try a power washer with a wide nozzle to get the haze off. It might work, it could be a paint job that’s faded from the sun.

Mix strong detergent, such as trisodium phosphate (TSP), with warm water in a plastic bucket. Proportions vary according to the type of detergent. A tablespoonful of TSP added to 1 quart of water may do the trick.

TSP: https://amzn.to/2UVCIgb

You can also try mineral spirits and a rag.

Mineral Spirits: https://amzn.to/2HGZWDC

Buy JoeMax and follow directions. Made our siding look new. You must be careful when using a power washer. Use low pressure.

https://www.hunker.com/13416946/how-to-remove-chalk-from-aluminum-siding