What was found
DURING DEPLANING AT THE GATE MODERATE AMOUNT OF SMOKE FILLED THE COCKPIT. WE SHUT DOWN THE APU AND SMOKE DISSIPATED IN APPROX. 2 MINUTES. FAS DID NOT NOTICE ANY SMOKE IN THE CABIN. WE LATER DETERMINED THAT RAMP SPRAYED RIGHT SIDE OF A/C WITH TYPE 1 FLUID EITHER BEFORE OR DURING OPERATION OF THE APU, BUT AFTER ARRIVING AT THE GATE. REMOVED FROM SERVICE. INSPECTED APU INLET FOR DEICE FLUID, NONE NOTED. C/W FUNC. TEST OF APU IAW Q400 AMM 49-00-00-720-801, FUNC. TEST GOOD, NO SMOKE NOTED. NO PARTS REPLACED. AIRCRAFT RETURNED TO SERVICE.