EMB ERJ 145 ER/LR
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Returned To Departure Airport; Flight Crew Took Evasive Action; General Declared Emergency
Aircraft
After takeoff the Captain (CA) and I noticed a fouled smell.  A burning smell that intensified in time.  It was my leg to fly and the CA decided to take over the control (after positive transfer of aircraft control) and decided to return the aircraft back to the airport. The CA radioed the tower and alerted them that we are declaring an emergency and to return back for immediate landing.  The tower said that we were cleared to land on runway XXR.  The flight clearance was to [fly a SID] but the tower instructed us to fly on a turn heading Northbound after takeoff.  During the turn thats when the CA and I noticed the smell.  We were on a right downwind to runways XXs when this problem occurred.  After landing successfully on XXR and cleared of the runway.  The CA and I performed the necessary checklist.  The CA then contacted the FA and she said that the smell was noticed from passengers sitting [near front of cabin].  We then proceeded to the gate with no additional problems as Emergency vehicles followed us.There were NO aircraft flying near our paths and no aircraft were told to deviate because of our path from departure; declaring the emergency; and turning towards the landing runway. Pilots and mechanics should get together and discuss the different types of odors that are associated with packs burning; electrical fires; and any other foul odor that may be encountered during all phases of flight in order identify the problem.  The CA told me once we were on the ground that [a previous] crash in the [...] started as a fouled smell in the cockpit and escalated into a tragedy.
The flight crew of an EMB-145 declared an emergency and returned to their departure airport after smelling a foul odor also detected in the cabin by passengers.