Chiral monoterpenes reveal forest emission mechanisms and drought responses.

Monoterpenes (CH) are emitted in large quantities by vegetation to the atmosphere (>100 TgC year), where they readily react with hydroxyl radicals and ozone to form new particles and, hence, clouds, affecting the Earth's radiative budget and, thereby, climate change. Although most monoterpenes exist in two chiral mirror-image forms termed enantiomers, these (+) and (-) forms are rarely distinguished in measurement or modelling studies. Therefore, the individual formation pathways of monoterpene enantiomers in plants and their ecological functions are poorly understood.