Isoprene, formula CH₂=C(CH₃)−CH=CH₂, is an organic, industrial  chemical largely supplied by the petrochemical industry.

When released into in the atmosphere, some of it oxidises to molecules that dissolve in water droplets producing a bluish haze, from which mountains like the Blue Mountains(New South Wales, Australia) and Blue Ridge Mountains (Eastern USA) derive their names.

But the “poor” trees (see picture) are not the victim but the “polluter”. Natural isoprene emission, mostly from trees, accounts for about a third of all global hydrocarbon emissions.

In the lower atmosphere (the troposphere), isoprene is quickly oxidised by ozone (O₃) that finds its way down from the ozone layer of ozone 20-30 km above. Up there in the stratosphere, O₃ is generated by solar radiation with about an eight of it renewed every day. The ozone layer is really important, shielding us from UV radiation, but down here in the troposphere O₃ is harmful to humans animals and plants. While isoprene depletes tropospheric O₃, nitrogen oxides in polluted air (e.g. from vehicle emissions) react with isoprene oxidation products and other organic pollutants to generate more tropospheric O₃, a significant consequence industrial pollution.

Isoprene occursin most organisms. Plants produce it as a precursor for other “isoprenoids”, including the carotenoids we discussed recently (Leaf 30) and many otherphytochemicals. Plants that produce copious isoprene tend to be more stressresistant, probably due to very active synthesis of antioxidant isoprenoids.

Isoprene can polymerise in plants to form natural latex. Synthetic rubber is isoprene polymerised industrially with additives to harden it. Natural and synthetic rubber are used widely, providing shoe soles, car tyres, stoppers for drinks and pharmaceuticals, etc..

So next time you see blue haze, you can look down at your shoes, look up towards the ozone layer, or look at the trees that produce the isoprene.

SOURCES:

📖 “Isoprene, Wikipedia https://en.wikipedia.org/w/index.php?title=Isoprene&oldid=1081789356

📖 Ozone–oxygen cycle, Wikipedia, https://en.wikipedia.org/w/index.php?title=Ozone%E2%80%93oxygen_cycle&oldid=1056093050

📖 Sharkey TD, Wiberley AE, Donohue AR. Isoprene emission from plants: why and how. Ann Bot. 2008 Jan;101(1):5-18. , https://doi.org/10.1093/aob/mcm240

‍