Isoprene emission from tropical tree species P.K. Padhy * , C.K. Varshney School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110 067, India Received 20 October 2003; accepted 15 October 2004 Isoprene flux (diurnal and seasonal) from some tropical tree species was estimated and a regional comparison was made. Abstract Foliar emission of isoprene was measured in nine commonly growing tree species of Delhi, India. Dynamic flow enclosure technique was used and gas samples were collected onto Tenax-GC/Carboseive cartridges, which were then attached to the sample injection system in the gas chromatograph (GC). Eluting compounds were analysed using a flame ionisation detector (FID). Out of the nine tree species, isoprene emission was found in six species (Eucalyptus sp., Ficus benghalensis, Ficus religiosa, Mangifera indica, Melia azedarach, and Syzygium jambolanum), whereas, in the remaining three tree species (Alstonia scholaris, Azadirachta indica, and Cassia fistula) no isoprene emission was detected or the levels of emission were negligible or below the detection limit (BDL). Among six tree species, the highest hourly emission (10.2G6.8 mgg ÿ1 leaf dry weight, average of five seasons) was observed in Ficus religiosa, while minimum emission was from Melia azedarach (2.2G4.9 mgg ÿ1 leaf dry weight, average of five seasons). Isoprene emission (average of six species), over five seasons, was found to vary between 3.9 and 8.5 mgg ÿ1 leaf dry weight during the rainy season. In addition, significant diurnal variation in isoprene emission was observed in each species. The preliminary estimate made in this study on the annual biogenic VOC emission from India may probably be the first of its kind from this part of the world. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Biogenic emission; Isoprene; Plant emission; Volatile organic compounds 1. Introduction Volatile organic compounds (VOC) play an impor- tant role in atmospheric chemistry. High levels of VOC in the ambient environment of Delhi have been reported (Varshney and Padhy, 1998; Padhy and Varshney, 2000a,b). However, emission of VOC from different sources and their strength remain unknown. Vegetation constitutes a prominent natural source of VOC emis- sion. Regional as well as global scale VOC emission, from vegetation, may dominate over anthropogenic sources of emission (Guenther et al., 1995). In India, the VOC emission inventory is available for anthropogenic sources (Varshney and Padhy, 1999) however no data is available on VOC emission from natural sources. Among various VOC species, isoprene is an impor- tant component of non-methane hydrocarbons, emitted by leaves (Warneck, 1988). Isoprene emission has been reported from a number of taxonomically unrelated plant species, such as bryophytes, ferns, conifers and in many families of angiosperm (Harley et al., 1999). Estimates based on the studies carried out on temperate plants, show that the isoprene emission constitutes about 40% of all biogenic hydrocarbons emitted into the atmosphere from vegetation (Zimmerman et al., 1978). A significant amount of fixed carbon, typically * Corresponding author. Present address: Centre for Environmental Studies, Institute of Science, Visva-Bharati University, Santiniketan- 731 235, Birbhum, West Bengal, India. Fax: C91 03463 261268/ 262728. E-mail address: padhypk2003@yahoo.com (P.K. Padhy). 0269-7491/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2004.10.003 Environmental Pollution 135 (2005) 101–109 www.elsevier.com/locate/envpol