Pluto really fascinates me, nearly as much as Titan. I think the action of UV radiation on methane in presence of nitrogen creates Tholins, a class of compounds which contain a wide array of organic molecules. These are probably the compounds mentioned in the article.

Did you know that because these molecules are under the form of an aerosol, in suspension in the atmosphere, they diffuse light as the molecules in the air do on Earth? In other word, the sky seen from Pluto would be like that of Earth on a Sunny day: Blue.

You can actually see it if you look closely at the haze on the pic: It’s blue.