Kennaook

The cleanest air

The Cape Grim Baseline Air Pollution Station, now officially Kennaook/Cape Grim, began measurements on 1 April 1976, at first from a caravan. At the western end of Tasmania, the winds of the Roaring Forties bring air that has not touched land since South America or the Southern Ocean, so that it represents the background atmosphere of the Southern Hemisphere. The Bureau of Meteorology runs the station and CSIRO leads the atmospheric research, as part of the Global Atmosphere Watch.

The dual name, joining the palawa kani name Kennaook with Cape Grim, was formally adopted in 2021.

The Air Archive

In 1978 the station started to store samples of air in stainless steel tanks, the Cape Grim Air Archive, held at CSIRO's laboratory in Melbourne. When new techniques or new interests arise, such as a new greenhouse gas, scientists can go back to the archived air and measure what it held decades ago. Studies of the archive show how the concentrations of halocarbons, methane and nitrous oxide rose and, for ozone-depleting substances, began to fall after the Montreal Protocol.

The station measures carbon dioxide, methane, nitrous oxide, halocarbons, ozone, aerosols and radon, along with weather and radiation.

Fifty years

The station marked fifty years of measurement in 2026, one of the three baseline observatories in the world's long record of atmospheric composition alongside Mauna Loa and the South Pole. Its location demands careful procedure: a measurement is taken only when the wind blows from the clean sector, from the south-west over the ocean, and a record of every wind direction is kept.

What baseline means

A baseline station is defined by what it excludes: local sources, the influence of cities and the contamination of the sample. At Cape Grim, the air is selected when it arrives from the south-west sector over the ocean, and measurements that do not meet the criteria are flagged. That choice makes the data representative of a large region and comparable with other baseline stations at Mauna Loa and the South Pole. It also means that the station's record excludes events, such as local bushfire smoke, that its neighbours care about, which are recorded in separate data. The definition of baseline is part of the data.

Instruments and technologies

• Gas chromatographs and analysers Instruments that separate and measure trace gases such as methane, nitrous oxide and the halocarbons in air drawn through a sampling mast.
• Cape Grim Air Archive Stainless steel tanks filled with compressed air and stored for later measurement.
• Baseline selection A wind sector and a condensation-nuclei count flag the times when air is background rather than local.

Timeline

• 1976 Measurements begin on 1 April, first in a caravan.
• 1978 Archived air samples begin to be stored at CSIRO's Melbourne laboratory.
• 2021 Dual name Kennaook/Cape Grim formally adopted.
• 2026 Station marks 50 years of measurements.

Key lessons for observation today

• Keep a sample for the question you cannot yet ask The Air Archive lets scientists measure gases nobody measured at the time. Archiving physical samples is a way to build future capability.
• Define what the site represents A baseline station records only when the air is clean. The rule for what counts as a valid observation belongs in the metadata.
• Honour the place The station's dual name acknowledges the Indigenous custodians of the land. A site is part of a community, and its name is part of its record.

Sources

• CSIRO, 50 years measuring the world's cleanest air
• CSIRO, Kennaook/Cape Grim Baseline Air Pollution Station
• Wikipedia, Cape Grim