cabin air intake

Does anybody know where the air that comes into the cabin comes in? I'm thinking of trying to fit a carbon filter into the air system, to minimize the fumes I'm choking on when sitting in traffic.

Jai

Comes in above the passenger's feet. There's a blower motor there, and the big cheap plastic hose that often comes un-done from the heater-core casing(for those who wonder where all that cold air is coming from in the winter). It takes air in from the fender-well.