I apoligize if this has been covered elsewhere in the forum... but I could really find anything...

I have a large 1 year old IPE deck oiled with Penofin in Downdown Chicago.

It looks great but a month after refreshing the penofin, it's dulling and has a solid coat of Chicago pollution sitting on top of it.

I'm looking for the proper solution to use for a good mid-season bath... this is NOT for prepping it for more oiling or anything like that--and I don't want to do anything that would prematurely strip out the last penofin coat. I just want a good dirt removing solution. I was amazed at how ineffective soap and water was.

Thanks in advance.