Hi Scott.
Okay - let’s see…
Upon being diagnosed with lung cancer, a lifetime litterbug tries to make the world beautiful for his depressed granddaughter before he dies.
Intention: to make the world beautiful. (I think this needs to be more specific. How so? How to make the world beautiful.)
Obstacle:
When his granddaughter is diagnosed with terminal cancer, a timid old man sets out to find a cure before it’s too late.
(In the process - he shows her the world is beautiful/or can be a beautiful place filled with good people.)
I’m not sure why he was a litterbug. (Or at least it’s not necessary to know in the logline.)
Good luck with this!