By C.K. Varshney, , Environews (Newsletter of ISEB India) Vol. 13 No. 1 - January 2007

It is widely known that green plants play a critical role in global carbon cycle by sequestering carbon dioxide from the atmosphere and converting it into organic compounds by using solar energy through the process of photosynthesis and releasing oxygen as a by product. In addition to oxygen plants from their green leaves have been shown to emit a number of complex organic compounds collectively called volatile organic compounds (VOCs). VOCs are a complex mixture of carbon; hydrogen compounds containing chemical species (excluding elemental carbon, carbon monoxide, and carbon dioxide), which are volatile at normal temperature and pressure. In precise terms VOCs are those organic compounds whose vapor pressure range from 0.13 kPa to 101.3 kPa at 293K. VOCs also include oxygenated, halogenated and sulphur containing hydrocarbons. VOCs are basically grouped into methane and non-methane hydrocarbons (NMHCs). VOCs are emitted both from anthropogenic and natural sources. The important anthropogenic sources on NMVOCs include, fossil fuel combustion, processing of organic chemicals and organic wastes. From anthropogenic sources globally 103 Tg NMVOCs are emitted yearly. The author and his co-workers at Jawaharlal Nehru University (JNU) have estimated that from India about 8 million tonnes of NMVOCs are emitted per annum.