Mark McCauley, a researcher at the University of Florida, says the air filters not only help provide important information on which species are present in a specific location, but also allow scientists to analyse "how changes in these species occur on geographical and temporal scales that would have been unforeseen until recently".

The regular monitoring provided by air filters is "unheard of in biodiversity science" and crucial to understanding species changes as it enables scientists to study the dynamics of animal populations and see how they are changing over time, says Clare.

Unlike single samples, such repeated measurements can "provide a really complete picture of what is happening in the area", says Clare. "You might detect the migration of a [particular] population, the arrival of a new species or a shifting landscape [due to] climate change."

The problem with current biodiversity monitoring is that there is no systematic method for doing it, says Littlefair. In the UK, for example, scientists rely heavily on data collected by "citizen scientists" to monitor species. This works for "charismatic species", such as butterflies and birds, but there are poor records for other species, such as fungi and nocturnal animals, which are less popular and more difficult to identify, she says.

"The great thing about environmental DNA from these [air quality] networks is that we can use it to go and look for any taxonomic group we want," says Littlefair.

But Clare warns that there are still "many unknowns", such as the impact of body size and activity on the DNA sampling. However, the assumption is that all species shed DNA and that "we should have equal probability of detecting something if it is within range," she says.

The new study is not the first to look at whether airborne particles can help identify species. A 2022 study by Clare and other scientists found that air in a zoo contains enough environmental DNA to identify the animals residing there. They analysed airborne DNA shed by animals, including breath, saliva, fur and faeces, and managed to detect 49 vertebrate species at Copenhagen Zoo.

Airborne DNA is a helpful tool for scientists as it allows them to detect "species that we cannot see are there", Kristine Bohmann, the study's lead author and a molecular ecologist at the University of Copenhagen, said when the study was published. It is also less resource-intensive and expensive than other biodiversity monitoring methods, which involve setting up camera traps or tracking footprints, she said.

Matthias Obst, an associate professor at the University of Gothenburg in Sweden, says there are several limitations when it comes to tracking biodiversity using air filters. These stations are often not operational in biodiverse places, he notes, and there is likely to be a much higher rate of false positives than in the case of conventional methods. The filters could, for example, capture DNA from a bird passing by or dust blown there by the wind.

"We must not get ahead of ourselves," he says. "Environmental DNA methods have great potential but there is little evidence in this article for an “biodiversity monitoring infrastructure."

Clare says filters aren’t just located in urban environments, but often found in national parks and biodiverse regions. She hopes the study will incentivise countries to set up stations in new locations of "significant ecological interest" and to preserve and archive the DNA captured by air filters.

"In many places environmental DNA [captured by air filters] is thrown away almost immediately. With this pilot study we have shown the ecological value of these samples, so we hope the data will be archived and studied," she says.

It may, Clare adds, prove an incredible treasure trove.