I've seen many a contrail being formed off many a tanker while A/R-ing. And I'm pretty sure there aren't any "spray nozzles" under the 135 wingtips.

I'll plagarize from wikipedia...

A vehicle engine's exhaust increases the amount of moisture in the air, which can push the water content of the air past saturation point. This causes condensation to occur, and the contrail to form. At high altitudes this water vapour emerges into a cold environment and the local increase in water vapour density condenses into tiny water droplets and/or desublimates into ice. The majority of the cloud content comes from water trapped in the surrounding air. At high altitudes, supercooled water vapour requires a trigger to encourage desublimation. The particulate matter in the aircraft's exhaust act as this trigger, causing the trapped vapor to rapidly turn to ice crystals