Cargo ships from a chemical facility are transporting chemicals down the coast to waiting trucks. The trucks are going to take the chemicals to a waiting transport plane. The transport plane will take off in an attempt to disperse the chemicals over friendly territory to the south. Stop the supply chain at any point and destroy the chemical facility to the north east of the enemy airfield.
I did not test this with anyone yet, so use at your own risk. This is my first time making a mission as well so I'd love to help, but I probably can't!