Isoprene emitted by trees has long been thought to form aerosols in the atmosphere, but how it does so was unclear.
Fabien Paulot of the California Institute of Technology in Pasadena and his colleagues used chemical ionization mass spectrometry to monitor the photooxidation products resulting from the reaction of isoprene with hydroxyl radicals in an experimental environmental chamber. They found that isoprene initially forms hydroxyhydroperoxides. Surprisingly, further reaction with hydroxyl radicals results in the production of dihydroxyepoxides and reformation of the hydroxyls. These epoxides are readily taken up by acidic aerosols, forming tetraols and polymers.
The researchers estimate that these expoxides account for nearly 100 teragrams of carbon in the atmosphere every year. Further understanding of this secondary aerosol formation should help to improve models of atmospheric chemistry.