National Oceanic and Atmospheric Administration scientists in Boulder were initially surprised when they discovered high concentrations of nitryl chloride in the local air at night: The pollutant is typically found in coastal areas, not the dry, high desert (Daily Camera). “During winter nights, scientists believe that nitrogen oxide pollutants–released from tail pipes and coal-burning power plants, among other sources–react with chlorine compounds found on the surface of particles suspended in the air,” the paper writes.

But now the scientists have a plan for studying the pollutant, which they believe is contributing to Denver’s brown cloud, thanks to “a government chemistry project launched Tuesday that uses a 985-foot-tall tower to sniff out a nasty new element of smog” (Denver Post).