Seven weeks of clearing the air provides huge benefits

Seven weeks of lockdown has provided evidence of how pollution can vanish overnight with benefits for the environment and individuals, says NIWA air quality scientist Dr Ian Longley. Dr Longley has been monitoring air quality in Auckland, Wellington and Christchurch since Level 4 restrictions were implemented and says working from home did not only cut emissions but could 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."

“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 estimates that while pollution was down by three-quarters on average, a least of third of Aucklanders reduced their exposure to traffic pollution by 90% 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. This is due to the disproportionately high influence diesel vehicles in downtown areas can have on air pollution exposure,” Dr Longley said.
Meanwhile, traffic pollution in Auckland was back at high levels today with the first morning of children returning to school, but Dr Longley said light winds would have helped drive that and it was too early to know if it had returned to pre-lockdown levels. And unless the way we work and travel changes, it is likely that it will be at least 15-20 years before New Zealanders experience the same levels of clean air as those achieved during lockdown.

Dr Longley says previous analysis showed that “business as usual” improvements in vehicle emissions technology means that we may achieve similar air quality as during lockdown, sometime 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% of normal and 25-35% of normal in level 4. The exception was at Queen Street, central Auckland, where the 55 % reduction during level-4 was unchanged in level-3.

Average nitrogen oxide (pollutant gases) concentrations compared to the norm for this time of year (based on 2015-2019).

Level-4

Level-3

Queen Street, AKL

46 %

45 %

Henderson, AKL

26 %

39 %

Takapuna, AKL

27 %

41 %

Penrose, AKL

34 %

51 %

Riccarton Rd, CHC

32 %

48 %


Dr Longley says the changes in traffic pollution are consistent with changes in traffic volumes. It is 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 exhaust.

During level 4 they were reduced by 9-15% of normal and in level 4 by 4-16%.

Dr Longley says it remains 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.”