Red Cabbage As Eruption Pollution Meter

One enterprising Icelander discovered a way to gauge levels of sulphur dioxide pollution, in a decidedly Icelandic way.

Sulphur dioxide from the Holuhraun eruption has been plaguing east Iceland for weeks now, and the noxious gas sometimes compels locals to stay indoors. When SO2 meters in the southeast town of Höfn í Hornafirði lost power on Monday night – during a time when SO2 levels were exceptionally high – one Icelander came up with a way to get an approximate idea of the presence of SO2 without the need for electricity, using a food dear to many Icelanders.

Vísir reports that chemist Sara Björk Sigurðardóttir, currently residing in Denmark, contacted her father Sigurður Mar Halldórsson, who lives in Höfn, with a proposal for detecting SO2 levels using nothing more than a plate of red cabbage (a traditional Sunday meal side, which goes exceedingly well with leg of lamb, sugar coated potatoes and canned peas).

Normally, the juice from braised red cabbage is violet. However, when exposed to a significant enough amount of acidity, the juice turns a brighter, pinkish purple. When sulphur dioxide comes in contact with water, it changes to sulphuric acid. Sara reasoned that the cabbage could therefore be used to detect the presence of SO2 in the air.

Following his daughter’s suggestion, Sigurður left a plate of braised red cabbage outside. Sure enough, the juice changed from violet to pinkish purple overnight.

While the experiment was successful, it cannot provide the detailed information of SO2 ppm that a sulphur dioxide meter can. Fortunately, the meters in Höfn have had their power restored.