Smoke and dust from the devastating bushfires along the New South Wales (NSW) and Queensland coastline turned New Zealand’s skies red—and ash to fall from the sky in some areas including Wānaka—last weekend.
There are more than 130 fires burning across the two states, with the number and severity of the fires prompting many to call the situation 'unprecedented' this early in the fire season.
"Smoke impacts from wildfires can reach thousands of kilometres downwind and even circle the globe. Where the smoke goes depends on the smoke plume release height and the atmospheric layer the smoke enters.” commented rural fire research leader Dr Tara Strand of Scion Rural Fire Research Group. "Queenstown just had a heavy smoke impact from the wildfires with ash falling from the sky. To get a smoke plume carrying ash from a wildfire that far away tells a story in itself. It says that: the wildfire was/is extremely large, the upper air atmospheric transport winds are strong, the wildfire behaviour is extreme, and there is likely a pyro-cumulous formation (when the fire creates its own weather).”
Strand added, "The reason for such large particles to be transported (or even formed en-route) means that the smoke must have been emitted very high in the atmosphere into the fast trans-Tasman winds that are high above the surface. To get the smoke that high a lot of energy is needed from the wildfire, indicating a large wildfire and a lot of heat generation. This usually results in a pyro-cumulous cloud forming above the fire."
In response to ‘What are the dangers, both in Australia and New Zealand, from the smoke?’, Strand said, “Smoke, in particular, particulate matter smaller than 2.5 micrometres (PM2.5) that makes up the majority of the smoke plume, is recognised globally as a pollutant due to its human health hazards. Particulate matter smaller than 2.5 micrometres can make it past our body's natural defences that filter out particles (i.e. the hairs in our nose) and go deep into our lung tissue and potentially into our bloodstream. Long exposure to smoke is not recommended for healthy individuals and sensitive individuals (i.e. asthmatics) need to monitor their exposure closely even in light smoke."
In response to ‘Are there likely to be any longer-term effects from the smoke?’ Strand said, "Black carbon (one of the components of PM2.5) is released from wildfires. Black carbon is known as a climate enhancer and it accelerates the melting of snow packs and glaciers when it deposits on snow or ice. For New Zealand, when the Southern Alps get impacted by smoke, this black carbon signature will be presented and this could cause accelerated melting."
Strand added, "For New Zealanders, our wildfire smoke exposure is likely to be minimal with the majority of the smoke aloft or very dilute, giving us spectacular sunrises and sunsets but no real large health impacts. But people should take caution if they feel they are impacted by smoke. The local health officer can assist with guidelines on what to do if exposed to smoke and of course, seek your GP if you feel ill or the hospital if you are having a medical emergency.”
In response to ‘How and why do dust/smoke clouds change the colour of the sky?’, meteorologist Ben Noll said, "When a beam of sunlight hits a particle in the atmosphere, something called scattering occurs. This sends some of the light’s wavelengths off in different directions and happens millions of times before that beam reaches your eye. Dust particles can help to create more scattering in the mid and upper atmosphere, which can increase the vibrancy of sunsets and sunrises.”
Noll added, "However, if the dust sits low in the atmosphere, it can actually have the reverse effect, leading to muted sunsets that are less colourful."
"It takes approximately 36-48 hours from the time a plume of dust or smoke leaves Australia to reach New Zealand," said Noll. "There were some reports of dust covering vehicles in the South Island over the weekend [...] Given the strong winds in the New Zealand region over the next week, no dust or smoke is expected to sit over the country for a prolonged period—each plume generally takes about 12 hours to pass across a given island."