Aluminum siding ?

[rvagnoni]

I was at a job yesterday and I was suppose to clean the aluminum siding of the house for the customer. When I first looked at the job, there were no signs of oxidation just, what I thought to be mildew...I was wrong... because it wasn't mildew it is some sort of roadway fallout from a nearby highway. Nothing I applied seemed to remove it. Does anyone have any suggestions on what I might try for this? I know the homeowner did use some sort of citrus based cleaner that they applied by hand and worked pretty well.

Also... the house recently had a new roof installed and the contractors had left shingle marks on the siding when they had torn off the old roof. Is there any kind of cleaner for removing those marks?