We purchase a Condo in Oct 03. From the time we took the key at closing and enter the home until now we have a very usual smell. I smelt like wet concrete. I was in the unit for 1 Hour and then went shopping. Everything that I had on and my purse smelt like this smell.
I have had the home tested for mold, bacteria, I have painted, I have numerous ozone cleanings, I have had my air conditioning coils cleaned. I have had the outside of part of the building power washed with Microban. I have put two new outside doors. I have had the walls scoped. I have infrared for moisture. And Nothing turns up. You will smell it upon entering the unit and then you don't smell it again. We stay for a week or two and then go home and everything smells Help

Sorry but being English rather than American I'm not 100% sure what a condo is. Is it like an apartment in a block of flats?
If so and the building is relatively new the small could be coming from the other apartments. It can take a long time for the new building small to dissipate if all the other apartments (or whatever you guys call them) aren't fully occupied. Once they are all filled and everyone uses plenty of heating and ventilation it should gradually fade.
If it's not a new building maybe recent work has been done on part of it?

I hope this is clear as we talk different languages on some things.

Well, THis has been going on for 6 years and the units are all filled and my unit according to the others is the only one that smells. I had my drywall tested for bacteria also and nothing

Oh my. Sorry out of ideas. Hope someone can help you.