New particle formation in forests inhibited by isoprene emissions

Atmospheric chemistry: forest isoprene clears the air Terrestrial vegetation releases vast amounts of volatile organic compounds (VOCs) into the atmosphere, mainly isoprene and derivatives such as monoterpenes and sesquiterpenes, some familiar as the aroma of pine trees. It has been suggested that these compounds are involved in the formation of organic aerosols, which act as 'seeds' for cloud formation and hence as cooling agents via an effect on radiative forcing. Experiments in a plant chamber simulating forest conditions show that isoprene can significantly inhibit new particle formation owing to its high hydroxyl radical reactivity. This surprising result may explain the observed seasonality in the frequency of aerosol nucleation events, as terpene emissions peak in summer, when there are fewer nucleation events than in autumn and spring. This work suggests that an increase in the isoprene content of VOCs in response to climate or land use change might reduce the potential for the formation of new aerosol particles, introducing a previously unrecognized element of climate warming.