Terrestrial vegetation releases vast quantities of volatile organic compounds (VOCs) to the atmosphere, of the order of 1 billion tons each year. Although of natural origin, biogenic VOCs (BVOCs) are central to our understanding of the role played by human activities in climate change and air quality issues. Most importantly, - they influence the oxidizing capacity of the atmosphere and therefore the abundance of e.g. the greenhouse gas methane, air quality compounds (e.g. carcinogenic benzene) and chemicals contributing to stratospheric ozone depletion (e.g. hydrochlorofluorocarbons); - in polluted areas, they participate to summertime (ozone smog) episodes, i.e. to the build-up of noxious pollutants, primarily ozone, due to the catalytic action of nitrogen oxides of anthropogenic origin; and - they are a source of Secondary Organic Aerosol (SOA) which makes up a substantial fraction of fine aerosols (i.e. particulate matter or PM).