Air quality improvements experienced during the Covid-19 lockdown have gone, with the most recent Waikato Regional Council monitoring results showing a return to normal concentrations.
For Waikato Regional Council chairman Russ Rimmington, the lockdown results "demonstrate that a move to low emission vehicles will make a huge difference to air quality".
"It also shows that our continued support and encouragement for industry to improve their emissions controls is quite justified when it comes to the health of our people and environment," he says.
Waikato Regional Council currently monitors air quality in seven airsheds across the Waikato region: Hamilton, Tokoroa, Te Kūiti, Taupō, Putaruru, Morrinsville and Thames.
Improvement in air quality (PM10 levels) was identified in three out of the seven monitored airsheds over the Covid-19 alert level 4 lockdown period.
A 21 per cent PM10 reduction in Hamilton and 11 per cent drop in Morrinsville is likely due to a reduction in emissions from traffic and also potentially a reduction in emissions from industry, according to council scientists. The average PM10 concentrations in both towns over the subsequent combined levels 3 and 2 period are back to levels expected at this time of year.
Te Kūiti experienced a significant 32 per cent reduction in PM10 concentrations during the lockdown, which was likely due mainly to a reduction in industry emissions with a more minor contribution from a reduction in traffic emissions. The average PM10 concentrations over the subsequent combined levels 3 and 2 period are back to normal.
No statistically significant changes in PM10 concentrations were observed for the other monitored airsheds over the different alert level periods.
Waikato Regional Council senior scientist Jonathan Caldwell explains the results could have been different had lockdown occurred during winter.
"In this case the lockdown occurred just as we were transitioning into autumn when the weather was initially warmer.
"But with people spending more time inside and temperatures starting to cool towards the end of lockdown, woodburner use was increasing which can confound the assessment of the impact of a reduction in traffic emissions."
Jonathan compared average PM10 concentrations in all seven airsheds over the level 4 lockdown period with the 33-day average for the same period over the last four years. He then did the same for the 33 days spent in levels 3 and 2.
"This is a more valid approach than comparing air quality directly prior to lockdown with air quality during lockdown, as air quality can be very variable from one day to the next," he says.
"This is due to differences in meteorology such as air temperature and wind speed and also differences in emissions from vehicles during a public holiday, for example.
"In New Zealand, air quality varies strongly with season, with the worst air quality experienced during the winter months when it gets colder and we experience more calm inversion type conditions coupled with a big increase in the number of woodburners operating."