The dust is not just from being a smoker. That just makes matters worse.
The air we breath is much more dirty than any of us would like to imagine and static electricity attracts it.
Computers are notoriously dirty in general for this reason.
Go to apple and try to get your screen replaced on apple care.
If you can't or your apple care is denied then you'll have to clean it on your own.
There are instructions from people like myself who have done it.
After you clean it do not seal it up tight. leave it open so that the smudges don't focus on just one area.
take the tape off the edges of the internal screen.
Watch for heat changes. It is not your fan that is the problem it is the expansion and contraction of air as the screen heats and cools that ***** the dust into the interior portion of your display.
Is it a design flaw? I think so. but it does not damage the screen it just makes it ugly and your computer will continue to work fine. If you do decide to attempt to clean the screen you must be VERY VERY careful. They are easy to break. I have damaged 2 of my 4 that I have tried to clean.
Best solution?
Buy a used mac pro!!!!
They'll last forever don't have the screen problems.
I just got my second 8 core 2.8 GHZ for 1300 plus a 23 inch monitor for 400 and I'm still cheaper than an IMAC and have 10 times the machine for the money!!!
I love APPLE!!!