C₅H₅, a colourless volatile liquid which is insoluble in water, soluble in alcohol, and very reactive because of its low vapour pressure and double bonds. From an atmospheric chemistry point of view, isoprene is emitted from trees and plants, globally on the order of teragrams (500 x 10¹² g) per year. This reactive, natural hydrocarbon may influence the oxidative/reductive balance in the biosphere where its concentrations are significant, in regions such as rainforests and large temporal forests. Most isoprene is directly emitted into the atmosphere from plant surfaces and some no doubt condenses on particulate matter. Emission rates from trees are positively correlated with leaf temperature and therefore, to a degree, time of day. Ultimately the carbon in isoprene is oxidised to carbon monoxide and finally carbon dioxide.