You've seen it when flying into major cities the world over: a haze over the city. It is caused by aerosol particles, but scientists don't know all the details of the complex chemistry involved. At Pacific Northwest National Laboratory, Dr. Alla Zelenyuk and her team took on a specific part of that haze: originated from isoprene. After being released by the trees and shrubs, isoprene reacts in the atmosphere and becomes assorted chemicals, including IEPOX (isoprene epoxydiols). The team found that IEPOX is a major player in producing aerosols from isoprene and that particle size, certain coatings, and acidity influence how IEPOX behaves.