A significant silver lining of the Covid-19 lockdown for Christchurch is the dramatic improvement in the city's air quality.
Nitrous oxide levels alone have dropped by 78 percent, the most substantial decrease anywhere in New Zealand, according to the report from the National Institute of Water and Atmospheric Research (Niwa).
Dr Ian Longley's report, Changes in NZ Air Quality due to Covid-19 Level 4 Lockdown, also noted an eight percent decrease in particulate matter levels in Christchurch.
Particulate matter levels are linked to traffic exhaust, but also pick up sources such as road dust, smoke from burning wood and coal, and even natural sources like sea salt (predominantly in Auckland).
In most places, those levels have not significantly decreased and that prompted a warning in the Niwa report that National Environmental Standards could be breached. An increase in particulate matter could come from the new normal; an increase of unemployment, working from home and social distancing, which would increase the time people spend heating their homes.
Despite that potential rise in particulate matter emissions, the report noted the current "extended period of improved air quality is unprecedented".
Environment Canterbury (ECan) senior science analyst Teresa Aberkane said the reduction in concentrations of air pollutants during lockdown was presumably due to a decrease in road traffic.
With restrictions easing, the concentrations that had reduced were expected to go back to what they typically were at this time of year.
Woodburners in homes were the main contributor to air pollution in this region, Aberkane said.
The Niwa report said future emission levels would depend on factors such a move to public or active transport, as well as an increase in alternatives to traditional transport.