By NIWA air quality scientists Dr Ian Longley
A thick river of smoke has been flowing across the Tasman Sea for over a month, tracked in detail by scientists using
satellite imagery. Most of the time the smoke passes to the north of New Zealand, or is removed by rainfall before it
reaches us. However, from time to time the smoke will inevitably reach our shores.
PM10 – a measure of particles in the air - is continuously measured at regional council monitoring stations in most
larger and some small towns. Smoke from Australian bushfires raised PM10 levels across North Island on 4th – 6th
A similar event has impacted South Island over the 1st – 2nd January. Monitoring data showed that PM10 levels rose for a
period of around 12 hours - increasing to 3 to 5 times normal levels - in a sequence starting in Southland in the
morning, crossing Otago in the afternoon and Canterbury in the evening.
The amount of smoke reaching each town is slightly different, as the smoke travels like a swirling, braided river with
thicker and thinner channels.
Much of the monitoring network in Otago is not operational in the summer due to air quality mainly being impacted by
winter home heating. However, NIWA’s prototype low-cost “ODIN” air monitoring network in Arrowtown clearly detected the
sudden arrival of the smoke there at around 10am, and lasting all day. Smoke levels were comparable to a typical
winter’s evening in Arrowtown, except this time the fires are over 2000 km away.
Where it was monitored, the smoke was neither thick enough nor persistent enough to breach National Environmental
Standards for Air Quality – which are expressed as an average over 24 hours. The average concentration of smoke that
impacted South Island were at most a third of the levels that have regularly been recorded in urban Sydney over the last
By the morning of the 2nd Jan the thickest part of this smoke ‘river’ had passed New Zealand and heading out into the
Pacific. However, a thinner remnant is leading to elevated PM10 being recorded in the top of South Island