e·mis·sion 
(ĭ-mĭshən)
(ĭ-mĭshən)n.
1. The act or an instance of emitting.
2. Something emitted.
3. A substance discharged into the air, as by an internal combustion engine.
[Latin ēmissiō, ēmissiōn-, a sending out, from ēmissus, past participle of ēmittere, to send out; see EMIT.]