Nicolas Nova's blog points us to MetPhoMod: the METeorology and atmospheric PHOtochemistry mesoscale MODel project (and don't blame me for the funky capitalization, that's what they use) in Switzerland. MetPhoMod is a 3D visualization tool for modeling meteorology and atmospheric chemistry -- that is, smog. MetPhoMod was used to study pollution patterns in Europe in the late 1990s, with a particular focus on the air chemistry over Grenoble and over the Swiss canton of Obwalden. The illustration at right is from work done in 1996 looking at smog patterns in Athens.
What makes this application interesting is the fact that it's free software, under a GPL license. The source code (as well as binaries for Solaris, AIX, Linux and Windows) can be found on the download page. A set of test data as well as data from a 1993 Swiss Plateau study are also available. The technical reference explains the theory and math behind the latest version of the app. MetPhoMod is complex stuff, clearly not meant for casual play, but I'm always happy to see these sorts of simulations made more widely available.