This morning between about 8.58am and 9.18am approximately, four passenger planes were seen spraying what appeared to be aerosols as they flew over Northland. Here is an image from Flightradar24.com of the four of them on what appeared to be, the same path over Northland: Four passenger planes over Northland. The identity of three of them was established using Flightradar24.com as: ANZ97, ANZ782 and KAL130.
The first one to pass in this time period of the four planes could not be identified using Flightradar24.com as it was not leaving a call sign. This was identified using the departures schedule from the Auckland Airport website as ANZ99, a Boeing 767-300 en route to Japan More: http://flightaware.com/live/flight/ANZ99. The trail it left was photographed spreading out.
KAL130, Registration HL7734 left Auckland Airport for South Korea according to the departure schedule, at 8.45am. It was photographed spraying an aerosol over Northland at about 9.18am. A second photo was taken 10 minutes later at about 9.28am to show the same trail KAL130 left behind, spreading out. See below.