Lockdown emissions secrets lurking in the lawn
The striking carbon-cutting effect of last year’s lockdown has been captured in blades of grass – revealing some sites saw CO2 levels plummet by 80 per cent as roads emptied.
The dramatic dent that Covid-19 restrictions put in our emissions last year has already been shown in Stats NZ data and local air pollution studies – but one project took a different tack.
That was in using grass clippings to gauge the change – and recruiting families around the country to send in their backyard samples for testing.
“As grass grows, it absorbs carbon dioxide from the air and gains energy from it using chlorophyll and sunlight,” explained Dr Jocelyn Turnbull,
who leads GNS Science’s radiocarbon and greenhouse gas research team.
“The carbon stored in the plant provides a useful recording of the radiocarbon content of the CO2 that has been absorbed.”
“The grass samples are ‘natural samplers’ of local air – and testing them gives us a weekly average of fossil fuel CO2 emissions.”
But because grass clippings reflected only local conditions – they captured only the environment within a 100m sq range – results varied depending on how close the sample site was to big emission sources such as roads and factories.
Volunteers across the country were called on to take cuttings from the same patch of grass at weekly intervals, as the country moved from level 4 lockdown to level 1.
“It was important that the location was the same every time to ensure that each sample was only the past weeks’ growth.”
Volunteers joined a Facebook group to learn how to take samples and the science behind the project.
Eventually, about 110 citizen scientists posted in samples that had been cut, dated, then stored in freezers.
The results – released yesterday for Earth Day – were remarkable.
Sites across Wellington, Christchurch, Hamilton and Gisborne all showed a 75 to 80 per cent drop in emission during level 4, compared to level 1.
Central Auckland locations also showed a decrease in emissions during lockdown, but not nearly as significant as Wellington sites, where emissions fell from 40 to 60 per cent.
“What we expect that we’re seeing with these central Auckland sites is a mixture of emission sources, not just traffic,” Turnbull said.
“We’re picking up residential and commercial emissions too, which we don’t expect to have dropped as significantly during lockdown.”