Although eDNA is already collected routinely from water, snow and soil, to gather information about biodiversity or to track contaminants or viruses, scientists have not typically monitored sources of DNA in air other than pollen and spores — robust packages designed to travel on the breeze.

But, in the early 2010s, various ecologists began to wonder whether air might contain useful DNA traces beyond those wrapped in such windborne bundles. In 2013, biologists Matt Clark at the Natural History Museum in London and Richard Leggett at the Earlham Institute in Norwich, UK, took air samples in a greenhouse and outside it.

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But it was the discovery of tiger DNA near Cambridge, UK, that alerted the wider community to airborne DNA’s potential. Elizabeth Clare at York University in Toronto, Canada, and Joanne Littlefair at University College London wanted to know whether they could find animal DNA in the air. They collected samples at a small zoo in Cambridgeshire, UK, reasoning that they would know the origin of any DNA they found, because the exotic animals were confined to the park.

In the laboratory, the researchers extracted the DNA from the samples, and amplified and sequenced it. They found that they could sniff out tigers 200 metres away from their enclosure, as well as many of the zoo’s other animals, their food — including chicken, horse and pig — and wildlife such as hedgehogs, bats and squirrels. In total, the samples contained DNA from 25 species of mammal and bird, including 17 kept at the zoo. Another study near Copenhagen Zoo, published at the same time, had similar findings.

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But it was a physicist who found a way to scale the method up. James Allerton, at the National Physical Laboratory in London, suggested that Clare examine samples taken by the UK Heavy Metals monitoring network, which has 25 air pumps, located in cities, in the countryside and at industrial sites.

The researchers studied samples from 15 of the network’s sites and, last year, published what they say is the world’s first national survey of terrestrial biodiversity using airborne eDNA. They found common UK animals, as well as exotic pets such as parrots and an invasive fish species, the silver carp (Hypophthalmichthys molitrix), that had not previously been reported in the region. From vertebrates to single-celled protists, they picked up 1,100 taxa.

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Ecologists are doing just that, documenting weekly, seasonal and cyclic fluctuations in the abundance of many species and matching these to climate variations. They have uncovered long-term community changes — the rise and fall in the abundance of pine trees because of changing forestry management, and a concomitant decline in other trees, mosses, lichens and fungi. They have tracked over time well-known co-variations between several species, such as those between flies and some bacteria, and found new ones.

Europe is dotted with radionuclide-detection stations, which could provide “an unprecedented opportunity to reconstruct ecological history and detect ongoing changes”, say Stenberg and his co-authors.

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But the idea of continuously collecting airborne DNA in public spaces troubles some scientists, who raise concerns similar to those about the sampling of DNA in waste water.

Breathe out on an evening walk and your DNA could waft into a discreetly placed urban sampler. Shotgun sequencing, using rapidly emerging, cheap, portable techniques that can generate the type of read-out that helps to identify individuals6, could produce results in the field, in near real time, says Duffy.

His team has shown this to be possible by sampling the air and unwashed windowpanes in Dublin and in Florida, from which they could distinguish between individuals of the same animal species. For ethical reasons, they did not try this type of sequencing for the human DNA that wound up in their samples, which is known as human genomic by-catch. But short-read analysis revealed human ancestries and some genetic diseases.