Atmospheric isoprene chemistry clarified

One of the key compounds emitted into the air by trees is isoprene. Once in the atmosphere, this common diene reacts with hydroxyl radicals and O₂ to produce six peroxy radical isomers. Those peroxy species affect air quality through reactions with nitrogen oxides and affect climate through reactions that form organic species able to condense into sunlight-reflecting aerosol particles. A new lab study digs into the complex and dynamic chemistry of isoprene-derived species, determining a comprehensive picture of their lifetimes and reaction rates (J. Am. Chem. Soc. 2017, DOI: 10.1021/jacs.6b12838). Alexander P. Teng, John D. Crounse, and Paul O. Wennberg of Caltech used an environmental chamber with mass spectrometry measurements to track yields of isomer-specific reaction products. The researchers found that the amounts of the peroxy radicals depend on their thermodynamic stability and the rate of hydrogen-shift intramolecular chemistry for two of the isomers. The results suggest that in typical atmospheric conditions β-hydroxyl peroxy radical isomers compose 95% of the radical pool, even though they are not initially formed in that proportion. In most prior laboratory studies, the peroxy radical pool reflected the nascent isomer distribution.