Broadcast trick that can improve the atmosphere? (6)
I believe the answer is:
aircon
'that can improve the atmosphere?' is the definition.
(aircon might improve the atmosphere)
'broadcast trick' is the wordplay.
'broadcast' becomes 'air' (to air on TV).
'trick' becomes 'con' (a con is a fraud or trick).
'air'+'con'='AIRCON'
(Other definitions for aircon that I've seen before include "Source of climate change" , "temperature control" .)