Traffic pollution tops pre-lockdown levels

Auckland’s traffic pollution has soared to levels higher than before the city was in lockdown, a scientist has revealed.

At the end of March, Auckland’s nitrogen oxide levels saw a steep dropoff, by as much as 90 per cent at times, for the first time in more than a decade.

But a scientific analysis of nitrogen oxide levels caused by road traffic exhaust shows that levels in the three days since the level-four lockdown ended had exceeded readings leading up to March 26, when the country was effectively closed.

Dr Ian Longley, an air quality scientist with the National Institute of Water and Atmospheric Research (Niwa), said high levels recorded at morning rush hour on Wednesday and yesterday were partly due to very light winds that had amplified the effect.

‘‘I was surprised to see the levels shoot up so high so quickly,’’ he said, ‘‘but it is likely they will return to pre-lockdown levels fairly quickly.’’

An analysis of air monitoring sites at Takapuna, Henderson and Penrose showed levels there were also up. At the same time, levels were lower in Queen St, possibly because fewer people were travelling into the centre of Auckland.

Nitrogen oxide levels have also returned to pre-lockdown levels in Christchurch but not as dramatically as in Auckland, he said.

During the five weeks of level four, traffic pollution was down at sites across Auckland – 54 per cent at Queen St, 66 per cent in Penrose, 73 per cent in Takapuna and 74 per cent in Henderson.

Niwa calculated the average concentrations between March 26 and April 27 and compared the result to the average over the same days from 2015 to 2019.

Longley said that up until the lockdown, there had been a consistent downward trend in nitrogen oxide levels that was connected to vehicle technology improvements.

‘‘If pollution levels revert to pre-lockdown levels and the same downward trend continued, it will take to the 2030s before air quality improves to that experienced during level four,’’ he said.

Meanwhile, compared with other cities around the globe, New Zealand’s cities were at the upper end of air quality improvements reported worldwide.

Longley said comparisons were difficult because of variation in how air quality is measured, but the European Environment Agency had published data showing reductions of 24 per cent in Milan, 26 per cent to 35 per cent in Rome, 55 per cent in Barcelona, 41 per cent in Madrid and 51 per cent in Lisbon.

More analysis has shown concentrations of dust, sea spray and smoke, known as particulate matter, were only marginally down across Auckland.