We're not sure if this is genius or utter lunacy - actually, we think we've got a pretty good idea - but the Defense Department has decided that it wants to know how each major city in the US smells, in order to help detect chemical attacks.
The Defense Advanced Research Projects Agency (DARPA) says it's looking to sample and analyze atmospheric trace gases in selected urban areaS. It wants to create a 'map' of these chemical signatures.
The idea is that if a city is subjected to a chemical attack, DARPA will be able to detect it through a change in the way the city smells - so much easier to spot than people coughing, choking and dying.
"These maps will provide chemical concentration data for subsections of typical urban areas comprised of a mix of residential and commercial buildings, highways, public transportation, and utilities," it says.
The maps will even need to take account of how the chemical mix changes over time.
"For example, dry cleaners and fast food restaurants will have particular chemical signatures; however, these may only be present during operating hours," says DARPA.
And because all this is dependent on the weather, it says, "This task will also collect meteorological data consisting of at least wind speed, wind direction, turbulence, temperature, relative humidity, barometric pressure, cloud cover, and solar insolation."
It's looking for partners to help build models for the maps.