Ambient Air Non-Methane Volatile Organic Compound (NMVOC) Study Initiatives in India--a Review (Report‪)‬

1. Introduction Volatile organic compounds (VOC) are ubiquitous atmospheric species of both natural and anthropogenic sources. These are wide range of chemicals including aliphatic and aromatic hydrocarbons, alcohols, aldehydes, ketones, esters and halogenated compounds sharing the same characteristics of high volatility in the ambient environment and result in alteration of the chemistry of atmosphere. On the global scale natural emissions of nonmethane hydrocarbons (NMHCs) and VOCs exceed anthropogenic emissions. Among the natural sources, vegetation is the dominant source. Oceanic and microbial production of these species is minimal as compared to other sources of input. On the other hand, anthropogenic sources are the result of urbanization and industrialization. This rapid urbanization and industrialization, at some places in a most unorganized way, is the general picture in developing countries around the world. The main concern of VOCs is the role they play in the formation of ozone and photochemical smog and increased risk of cancer. Thereby it is quite evident that although in rural areas natural vegetation causes VOC emission, due to lower N[O.sub.x] concentration, O3 production is less; which is not the case in urban atmosphere, where due to the industrial and vehicular pollution the relative concentration of N[O.sub.x] reaches up to a level so that it easily contributes to production of O3 even in small concentration of NMHCs. In polluted areas with relatively high concentration of N[O.sub.x], photochemical oxidants of NMHCs, initiate a complex series of photochemical reactions that lead to the production of [O.sub.3] and other secondary oxidant pollutants [1]. The emission of VOCs thus have much more detrimental effect in urban areas and the percentage concentration of VOCs in ambient air, their source profile identification and effect on health due to exposure should be well understood to undertake a successful planning of metropolis or establishment of industrial belt.