Air pollution in New Zealand's main centres plummeted by three quarters during lockdown – showing how quickly smog can vanish, with benefits for our health and environment.
Data released by Niwa today also showed how a third of people in Auckland would've been spared nearly all traffic pollution.
Air quality scientist Dr Ian Longley has been monitoring air quality in Auckland, Wellington and Christchurch since alert level 4 restrictions were implemented, and says working from home can not only cut emissions but also reduce health risks.
"Lockdown has provided vivid confirmation of how in New Zealand cities, isolated from each other and international neighbours, and where heavy industry is largely absent, many pollutants can be made to almost disappear overnight," he said.
"But although air quality changed dramatically across the cities we monitored - and probably all other towns and cities too - the benefits would not have been experienced equally."
He estimated that while pollution was down by three quarters on average, at least a third of Aucklanders reduced their exposure to traffic pollution by 90 per cent during lockdown.
"This gain could have been extended to a few hundred thousand more people if diesel trucks and buses had been removed from the city centre," Longley said.
This was due to the disproportionately high influence diesel vehicles in downtown areas could have on air pollution exposure.
And unless the way we work and travel changed, it was likely that it would be at least 15 to 20 years before New Zealanders experience the same levels of clean air as those achieved during lockdown.
Previous analysis showed that "business as usual" improvements in vehicle emissions technology means that we may achieve similar air quality as during lockdown, some time in the late 2030s "if at all".
Overall, concentrations of road traffic pollution in Auckland, Wellington and Christchurch during level 3 were between 47 and 63 per cent of normal and 25-35 per cent of normal in level 4.
The exception was at Queen St, central Auckland, where the 55 per cent reduction during level 4 was unchanged in level 3.
Average nitrogen oxide concentrations compared to the norm for this time of year.
Longley said the changes in traffic pollution were consistent with changes in traffic volumes and it was likely the volume of heavy duty traffic in the Auckland CBD changed less than in other places.
There were also reductions in the amount of particulate matter in the air from traffic, heating, industrial and natural sources, however these were lower than traffic exhausts.
During Level 4 they were reduced by nine to 15 per cent of normal and in Level 4 by four to 16 per cent.
It remained to be seen whether these reductions in exposure to air pollution will translate into improvements in health.
"The exposure of a large number of people worldwide to a sustained reduction in traffic pollution, but not particles from other sources, is a rare occurrence that provides a natural experiment to improve our understanding of the different health impacts of different forms of air pollution."
Meanwhile, traffic pollution in Auckland was back at high levels today with the first morning of children returning to school, but Longley said light winds would have helped drive that and it was too early to know if it had returned to pre-lockdown levels.
Globally, further new research showed levels two major air pollutants have been drastically reduced since lockdowns began in response to the Covid-19 pandemic, but a secondary pollutant - ground-level ozone - has increased in China.
Two new studies in the journal Geophysical Research Letters find nitrogen dioxide pollution over northern China, Western Europe and the US decreased by as much as 60 per cent in early 2020 as compared to the same time last year.
Particulate matter pollution – or particles smaller than 2.5 microns - has decreased by 35 percent in northern China.
Particulate matter is composed of solid particles and liquid droplets that are small enough to penetrate deep into the lungs and cause damage.
Such a significant drop in emissions was unprecedented since air quality monitoring from satellites began in the 1990s.
The only other comparable events are short-term reductions in China's emissions due to strict regulations during events like the 2008 Beijing Olympics.
The improvements in air quality were likely to be temporary, but the findings gave scientists a glimpse into what air quality could be like in the future as emissions regulations become more stringent.