The website Chemtrails Project UK has on its front page a slideshow of chemtrail bunk that includes a picture that is purported to show a "chemtrail plane":
A reverse image search of that plane photo shows that it is a screenshot from a YouTube video, which also claims to show a chemtrail plane, filmed from another aircraft.
This plane appears to be an Airbus 340, and close examination of the video reveals the registration number on the wing:
F-GLZC is an Airbus A340-312 owned by Air France. A photo of the plane shows that the livery matches - all white, with dark stripes on the tail.
Photo from http://www.planespotters.net/Aviation_Photos/photo.show?id=377170&from=flightradar_200
A reverse image search of that plane photo shows that it is a screenshot from a YouTube video, which also claims to show a chemtrail plane, filmed from another aircraft.
This plane appears to be an Airbus 340, and close examination of the video reveals the registration number on the wing:
F-GLZC is an Airbus A340-312 owned by Air France. A photo of the plane shows that the livery matches - all white, with dark stripes on the tail.

Photo from http://www.planespotters.net/Aviation_Photos/photo.show?id=377170&from=flightradar_200