Residual light as fog later dispersed (9)
I believe the answer is:
afterglow
'residual light' is the definition.
(I've seen this before)
'later dispersed' is the wordplay.
'later' becomes 'after' (I've seen this before).
'dispersed' becomes 'glow' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'after'+'glow'='AFTERGLOW'
'as fog' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for afterglow that I've seen before include "Post-sunset radiance" , "following which gloom sets in?" , "residual light" , "Light once the actual source has gone" , "appearing when sun has set?" .)