One of many conundrums in climate science is that atmospheric models underestimate the high masses of airborne organic aerosol particles, which spawn haze and clouds that block the penetration of solar radiation to Earth. Volatile organic compounds emitted by forests are thought to be an important source of some of these aerosols, but the exact mechanisms by which these molecules become solid particles have remained a mystery. An international research team led by Mikael Ehn of the University of Helsinki, in Finland, reports that rapid oxidation of forest volatiles, particularly terpenes such as α-pinene, may be an important mechanism for some of this mysterious aerosol production (Nature 2014, DOI: 10.1038/nature13032). Working in laboratory chambers that mimic the air above boreal forests, Ehn’s team showed that only a few oxidation reactions are required to condense α-pinene and other terpenes produced by the foliage to aerosol particles. The work “can only improve our predictive capability and potentially close the gap between bottom-up models and atmospheric observations,” notes University of Manchester climate chemist Gordon B. McFiggans in commentary about the work (Nature 2014, DOI: 10.1038/506442a).