1994 Honda Civic Bad odor with the outside vent on

In the past few months, my Honda has been smelling bad inside with the vent open. It even smells bad when I'm recirculating the air.

Some people have said it smells like mold. Others have said it is more of a "chemical" smell -- I lean towards the latter. I have no idea what it could be.

The car just passed the California smog test from a "test only" station, if that info helps.

Thanks!