Seven weeks of lockdown has caused an "unprecedented" reduction in air pollution, NIWA has revealed.
NIWA air quality scientist Ian Longley says pollution was down by 75 percent across Auckland, Wellington, and Christchurch.
Longley told Newshub that it would have had benefits for New Zealanders' health.
"Basically we're looking at gases which come largely from road traffic and other sources like industry and shipping as well - that's been down by about two-thirds to three-quarters pretty much everywhere where it's being measured.
"That's unprecedented really and should make a big difference for public health.
"What the lockdown experience has shown is as soon as we stopped driving around - which was pretty much instantly at the beginning of level 4 - the air quality responded instantly."
Longley said going back to normal puts pollution levels right back where they were.
"As soon as we start getting back into our cars and trucks, as we are doing at the moment, the pollution levels are tracking back up," he told Newshub.
"Whether we actually reach normal or we have a new normal from now on remains to be seen.
"Generally, I like to say New Zealand has really good air quality most of the time, in most places."
Longley said people need to think about how to get around in day-to-day life.
"I think the lockdown has shown, actually, we can do an awful lot - it's the collective action of lots of individual businesses, agencies, Governments, and people.
"This has really shown that collectively, all those little decisions can make a huge difference and can make an instant difference.
"What we've really done now is learn how we can accelerate improvements in our air quality and hopefully get the air quality we experienced during lockdown back again in the not too distant future."