Isoprene emission from Indian trees

Transcription

1 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D24, 4803, doi: /2003jd003866, 2003 Isoprene emission from Indian trees C. K. Varshney and Abhai Pratap Singh School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, India Received 16 June 2003; revised 18 September 2003; accepted 24 September 2003; published 31 December [1] Isoprene is the most dominant non-methane volatile organic compound (NMVOC) emitted by plants. NMVOCs play an important role in regulating the composition of atmospheric trace gases including global concentration of tropospheric ozone. Our present knowledge about NMVOCs emission is mainly from studies on temperate tree species. So far information on biogenic NMVOCs emission from tropical tree species is limited. In this study, isoprene emission rates from 40 tropical Indian tree species belonging to 33 genera and 17 families were measured for the first time using a dynamic flow through enclosure chamber technique. The isoprene emission rate from plants (30 C and PAR 1000 mmolm 2 s 1 ) ranged from undetectable to 81.5 mgg 1 h 1 and values were found to be comparable with other studies on tropical tree species. Tree species screened for isoprene emission in the present study may be grouped into the four categories, proposed by Karlik and Winer [2001], namely, 18 species were negligible or BDL isoprene emitting (<1 mg g 1 h 1 ), 6 species were low emitting (1 to <10 mg g 1 h 1 ), 5 species were moderate emitting (10 to <25 mg g 1 h 1 ), and 11 species were high isoprene emitting (25 mg g 1 h 1 ). Maximum isoprene emission rate (81.5 mg g 1 h 1 ) was observed in the case of Dalbergia sissoo Linn. It was interesting to find that Citrus limon Linn., Citrus reticulata Linn., Citrus sinensis Linn., Grevillea robusta A. Cunn., and Morus alba Linn., which were earlier reported as BDL or non isoprene emitters in US [Winer et al., 1998; Karlik and Winer, 2001] were found to be appreciably high isoprene emitters ( mg g 1 h 1 ) in the present study. INDEX TERMS: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 Atmospheric Composition and Structure: Pollution urban and regional (0305); 0368 Atmospheric Composition and Structure: Troposphere constituent transport and chemistry; 0399 Atmospheric Composition and Structure: General or miscellaneous; KEYWORDS: nonmethane volatile organic compound, tropical trees, isoprene emission Citation: Varshney, C. K., and A. P. Singh, Isoprene emission from Indian trees, J. Geophys. Res., 108(D24), 4803, doi: /2003jd003866, Introduction [2] Non-methane volatile organic compounds [NMVOCs] play an important role in determining the oxidizing capacity and aerosol burden of the atmosphere [Fehsenfeld et al., 1992]. They exert a strong influence on chemical composition of the atmosphere and on global climate change [Hewitt and Street, 1992; Steinbrecher et al., 1997]. There are many sources of the atmospheric NMVOCs. Isoprene emission from vegetation is the world s largest known source of non-methane volatile organic compounds, which represents a direct transfer of reactive carbon from plants to the atmosphere. It is estimated that over 90 per cent of isoprene emissions are from vegetation [Guenther et al., 1995]. Isoprene is highly reactive NMVOCs having atmospheric lifetime of 0.2 days. The oxidation of isoprene in the atmosphere (a) produces large quantities of CO [Zimmerman et al., 1978]; organic acids [Chameides et al., 1992] and ozone [Jacob and Copyright 2003 by the American Geophysical Union /03/2003JD Wofsy, 1988] (b) increases the lifetime of methane in the atmosphere [Wuebbles et al., 1989]. Isoprene emission from vegetation is influenced by many factors, including ambient temperature [Tingey et al., 1979], sun light [Harley et al., 1996], CO 2 concentration [Monson and Fall, 1989], genetics [Monson et al., 1994], leaf development, growth stage of plants [Monson et al., 1994; Street et al., 1996], phenological events [Robertson et al., 1995], time of the day and the season [Guenther, 1997]. Accordingly, NMVOCs emission from plants is highly sensitive to land cover (plants composition and dominance) and environmental conditions. Most of the studies on the biogenic NMVOCs emission are from trees of temperate region. However, according to Guenther et al. [1996, 1999], at least 50 per cent of the global annual isoprene fluxes are from tropical ecosystems. Measurements on VOC emission from tropical tree species are limited [Guenther et al., 1996; Lerdau and Keller, 1997; Klinger et al., 1998; Keller and Lerdau, 1999; Kuhn et al., 2002; Geron et al., 2002; Harley et al., 2003] and they are altogether lacking from the Indian subcontinent. Accord- ACH 24-1

2 ACH 24-2 VARSHNEY AND SINGH: ISOPRENE EMISSION FROM INDIAN TREES ingly, it is difficult to make an assessment of VOC emission for the Indian subcontinent. This study reports isoprene emission from 40 tropical tree species of India. 2. Experimental Methodology [3] Forty tree species widely occurring throughout the Indian subcontinent belonging to 33 genera and 17 families were selected for this study (see Table 1). Five to eight year old saplings of individual tree species were obtained from local commercial nurseries and maintained in the earthen pots containing fertile garden soil mixed with organic manure in the ecological garden. Plants were watered at regular intervals Sampling Methods and Program [4] A dynamic flow through enclosure system as employed previously by Winer et al. [1983] and Street et al. [1996], was used for emission measurements. The enclosure chamber was constructed from 0.25 mm transparent polycorbonate sheet measuring approximately cm 3. The enclosure chamber was equipped with a fan and inlet and outlet ports suitable for introduction of matrix air and withdrawal of analytical samples respectively. The enclosure was carefully fitted around the stem of tree sapling in order to minimize any effect from rough handling. Air was passed through enclosure chamber at a rate of 20 l/min and this flow was maintained for 20 minutes prior to sampling. Samplings were carried out for 10 minutes as described by Winer et al. [1983] at a rate of 0.10 l/min from enclosure on to Tenax TA (200 mg)/carboseive (100 mg) II solid adsorbent [Obtained from Supelco Inc. Bellefonte, PA]. The packed Tenax TA/carboseive tubes were preconditioned by heating at 300 C for several hours with continuos purge of nitrogen. After sampling Tenax tubes were sealed with Teflon ferrules and stored at 4 C and the samples were analysed within 30 minutes. [5] For each individual species 6 8 samples were taken at stretch over 3 5 days during day light hours between 9.0 am 5.30 pm. Most of the samples were taken between 9.0 am 11.0 am and 3.0 pm 5.30 pm in order to avoid high temperature build up inside chamber. Temperature and photosynthetically active radiation (PAR) were measured both inside and outside the chamber with the help of thermometer and Li Cor Quantum sensor (Model LI-185) respectively. Inlet and outlet airflow rates of enclosure chamber were measured by calibrated rotameter Gas Chromatographic Analytical Methods [6] A Nucon gas chromatograph (Model 5765, Nucon Engineers, Okhla, New Delhi) with a fused silica capillary column (length: 30 m, id: 0.53 mm, bonded phase BP-I, Alltech Associates, Dearfield, IL, USA) connected with flame ionization detector (FID) was used for isoprene determination. Compounds were desorbed at 280 C for 8 minutes onto a Tenax TA/carboseive by a thermal desorber injection system attached with the GC. The initial oven temperature was maintained at 40 C for 5 minutes, then increased to 180 C at a rate of 5 C/min for 5 minutes thereafter temperature increased at a rate of 15 C upto 250 C and maintained for 10 minutes. N 2 was used as carrier gas and the flow rate was maintained at 8 ml/min, the injection temperature was 230 C and detector temperature was 250 C. Isoprene in the samples was determined with the help of a standard calibration plot prepared from the standard isoprene obtained from Fluka/Sigma-Aldrich, USA. Gas phase standard was prepared by serial dilution of isoprene liquid chemical standard in 500 ml round flask fitted with screw cap syringe sampling ports. The precision and accuracy of the GC/FID system were about 4 per cent as determined by repeated measurements of the standard gas. The lower detection limit of analytical system was 2 ppb (v/v) for isoprene Dry Foliar Biomass Determination [7] After the emission flux measurements were completed, the entire branch, which has been enclosed in the chamber, was harvested, and the leaves were stripped off the stems and then dried in an oven at 70 C to a constant weight Normalilizing Emission Rates [8] Measured isoprene emission rates were normalised to PAR and temperature of 1000 mmolm 2 s 1 and 30 C, respectively, using the algorithm proposed by Guenther et al. [1993] and subsequently modified by Guenther [1997]. [9] In this algorithm, isoprene emission rates are described as I ¼ MR=C L :C T I is normalized isoprene emission rate (mgg 1 h 1 ) predicted at temperature T (K) and PAR L (mmolm 2 s 1 ) and MR is measured emission rate. [10] The two variables C L and C T are respectively light and temperature coefficients derived from experimental measurements on Eucalyptus, Sweet gum, Aspen, and Velvet bean and are defined by C L ¼ a:c L1 :L= 1 þ a 2 1=2 þ L Where L was the PAR (mmolm 2 s 1 ) C L1 was an empirical coefficient (1.067) and a was an empirical coefficient (0.0027) C T is calculated as follows: C T = exp {CT 1 (T Ts) (R.Ts.T) 1 }/ exp {C T2.(T Tm) (R.Ts.T) 1 } Where T was the leaf temperature in degrees Kelvin R was a gas constant (8.314 JK 1 mol 1 ), Ts was the normalizing temperature in degrees Kelvin Tm was an empirical coefficient (314 K), C T1 was an empirical coefficient (95,000 J mol 1 ), and C T2 was an empirical coefficient (230,000 J mol 1 ) The leaf temperature was not measured. Hence the temperature of the well-mixed air inside the enclosure was used to normalize the emission rates. 3. Results and Discussion [11] Mean isoprene emission rate (30 C and PAR 1000 mmolm 2 s 1 ) of individual tree species along with average temperature, PAR and the number of emission samples for each species are given in Table 1. The mean

3 VARSHNEY AND SINGH: ISOPRENE EMISSION FROM INDIAN TREES ACH 24-3 Table 1. Mean Isoprene Emission Rate (mg g 1 h 1 ) From Forty Indian Tree Species Scientific Name Local Name Isoprene Emission Rate No. of Enclosure Run Avg. Temp., C Avg. PAR, mmolm 2 s 1 Anacardiaceae Mangifera indica Linn. Aam 26.0 ± Bignoniaceae Heterophragma adenophyllum Benth & Hook. Maronfali 0.50 ± Kigelia pinnata DC. Kigelia 1.0 ± a Bombacaceae Ceiba petendra Linn. Ceiba BDL a Chorisia speciosa St. Hill. Kuregia BDL a Salmalia malabarica DC. Semul 4.20 ± Casuarinaceae Casuarina equisetifolia Linn. Vilayti- Jhau 20.4 ± a Combretaceae Terminalia arjuna Roxb. Arjun BDL Terminalia bellirica Roxb. Bahera BDL Ehretiaceae Cordia obliqua Willd. Lasoora 1.50 ± a Fabaceae Butea monosperma Lamk. Dhak ± a Dalbergia sissoo Linn. Shisham 81.5 ± Pongamia pinnata Linn. Papari 33.0 ± Lauraceae Cinnamomum tamala T.Nees & E. Berm. Tejpat 27.1 ± a Cinnamomum zeylanicum Bereyn. Dalchini BDL a Meliaceae Azadirachta indica A.Juss. Neem BDL a Melia azedarach Linn. Buckain BDL a Chukrasia tabularis A.Juss. Chikrasi BDL Mimosaceae Acacia nilotica Willd. Desi babool BDL a Albizzia lebbeck Linn. Siras 0.66 ± a Pithecellobium dulce Roxb. Jangal Zalebi 21.5 ± a Moraceae Ficus benghalensis Linn. Bargad 37.0 ± F. glomerata Roxb. Gular 47.6 ± F. infectoria Willd. Pilkhan 52.0 ± F. religiosa Linn. Peepal 76.5 ± Morus alba Linn. Sahtoot 21.6 ± Myrtaceae Eucalyptus globulus Labill. Safeda 55.6 ± a Psidium guajava Linn. Amrood 31.5 ± a Syzygium jambolanum DC. Jamun 25.0 ± Proteaceae Grevillea robusta A. Cunn. Silk-Oak 16.2 ± a Rutaceae Aegle marmelos Linn. Bel BDL Citrus reticulata Santara 0.92 ± Citrus limon Linn. Nimbu 0.61 ± Citrus sinensis Linn. Mausambi 0.70 ± Murraya koenigii Linn. Meethi Neem BDL Rhamnaceae Zizyphus jujuba Lamk. Ber 1.65 ± Sapotaceae Manilkara hexandra Roxb. Khirni BDL Achras zapota Linn. Chiku 38.0 ± a Sterculiaceae Sterculia alata Roxb. Estercolia BDL a Pterospermum acerifolium Willd. Knakchampa 1.20 ± a Emission measurements in summer months (April, May, June). Values without footnotes indicate measurements during Autumn ( Sept., Oct., Nov. months). BDL: below detection limit.

4 ACH 24-4 VARSHNEY AND SINGH: ISOPRENE EMISSION FROM INDIAN TREES Table 2. A Comparison of the Observed Isoprene Emission Rates From Six Tree Species With the Values Reported in Literature Scientific Name Local Name Present Study, mg g 1 h 1 Literature Data, mg g 1 h 1 Reference Acacia nilotica Desi Babool BDL BDL Harley et al. [2003] Citrus limon Nimbu 0.6 BDL Winer et al. [1989] Citrus sinensis Mausambi 0.7 BDL Winer et al. [1992] Ceiba petendra Ceiba BDL 0.0 Klinger et al. [1998] Eucalyptus globulus Safeda Street et al. [1997] 57.0 Evans et al. [1982] 28.0 Pio et al. [1996] Grevillea robusta Silk oak Winer et al. [1998] Morus alba Sahtoot 21.6 a 0.0 b Karlik and Winer [2001] BDL, below detection limit. a Isoprene emission rate values for fruit-bearing Morus alba. b Isoprene emission rate values for fruitless Morus alba. isoprene emission rates varied from undetectable to 81.5 ± 30.7 mg g 1 h 1. Maximum isoprene emission rate was observed in the case of Dalbergia sissoo Linn. [12] Tree species screened for isoprene emission in the present study may be grouped into the four categories, proposed by Karlik and Winer [2001], namely, 18 species were negligible or BDL isoprene emitting (<1 mg g 1 h 1 ), 6 species were low emitting (1 to <10 mg g 1 h 1 ), 5 species were moderate emitting (10 to <25 mg g 1 h 1 ), and 11 species were high isoprene emitting (25 mg g 1 h 1 ). Based upon above criteria 45 per cent of the species were non-detectable emitters, 15 per cent low, another 12.5 per cent moderate and the remaining 27.5 per cent were high emitters. [13] Out of the total 40 tree species screened during this study, isoprene emission from 34 tree species has been reported for the first time including the first report for any species of family Ehretiaceae. Accordingly, family Ehretiaeceae represents a new addition to the known list of 122 isoprene emitting plants families [Harley et al., 1999]. Only for seven species, out of the 40-tree species isoprene emission values have been reported in literature [Evans et al., 1982; Winer et al., 1989; Winer et al., 1992; Street et al., 1997; Klinger et al., 1998; Winer et al., 1998; Karlik and Winer, 2001; Harley et al., 2003]. Isoprene emission rates of these seven species have been compared with the values reported in the literature (Table 2). It may be observed that Citrus limon Linn., Citrus sinensis Linn., Grevillea robusta A. Cunn., and Morus alba Linn., earlier reported as negligible or BDL isoprene emitters [Winer et al., 1998; Karlik and Winer, 2001] were found to be relatively high isoprene emitters ( mg g 1 h 1 ) in the present study. It may be pointed out that in our investigation fruit bearing variety of Morus alba plants were taken, whereas values reported by Karlik and Winer [2001] were for the fruitless variety of Morus alba. Discrepancies in isoprene emission in respect of some plant species have been also observed by other workers [Kesselmeier et al., 1996, 1998; Geron et al., 2002]. For example, all North American oaks were reported as high isoprene emitters, in contrast to European oaks, which were found to be non emitters [Kesselmeier et al., 1996, 1998]. Similarly, Geron et al. [2002] have reported Pentaclenthra macroloba (Willd.) and Zygia longifolia (Humb. & Bonpl.) as significant isoprene emitters in Costa Rica; in comparison to this their counter part African populations were reported as non emitters [Klinger et al., 1998; Rasmussen, 1978]. In case of Eucalyptus globulus, apart from our study, values reported for by Evans et al. [1982], Pio et al. [1996], Street et al. [1996] show considerable variation (Table 2). These variation may be on account of a differences in plants genetic make up [Monson et al., 1994], physiological status, leaf age [Monson et al., 1994; Steinbrecher et al., 1997], leaf nitrogen status [Harley et al., 1994], or due to variation in the experimental methodology employed to measure emission rate. The observed variation in isoprene emission among populations of the same species is quite interesting and needs to be explored further to ascertain the underlying cause and the ecological significance. A large inter and intraspecies variation in isoprene emission rates was observed during the study (Table 1). Maximum intraspecies, i.e., plant to plant, variation was observed in Dalbergia sissoo. [14] The following five families namely, Anacardiaceae, Casuarinaceae, Fabaceae, Moraceae, Myrtaceae, and Proteaceae were found to be moderate to high isoprene emitter on the basis of limited number of taxa of each families screened during the study. On other the hand, Bignoniaceae, Bombacaceae, Ehretiaceae, Rutaceae, and Sterculiaceae were found to be negligible or low isoprene emitters. Isoprene emission was found to be below detection limit (BDL) in all species belonging to family Combretaceae and Meliaceae. Certain families such as Bombacaceae, Fabaceae, Lauraceae, Mimosaceae, Moraceae, Myrtaceae and Sapotaceae exhibited a wide variation of isoprene emission rates (see Table 1). [15] Benjamin et al. [1996] have proposed a taxonomic method for assigning specific isoprene emission rates at family and genus levels. Measured isoprene emission rates were compared with the specific isoprene emission rates assigned by Benjamin et al. [1996] (Table 3). Isoprene emission rates assigned at genus level were within ±50 per cent of the measured isoprene emission rates. However, differences between the measured emission rates and the assigned values at the family level were >50 per cent (see Table 3). In light of these observations, emission rates values assigned at genus level appear more representative in contrast to the family level assignment, not withstanding inter species variation. [16] A direct comparison of the results of this study with the published data is difficult because the published reports pertain to the measurements of atmospheric levels of isoprene in the tropical forests [Kesselmeier et al., 2000; Crutzen et al., 2000; Kuhn et al., 2002; Holzinger et al., 2002]. Moreover, the reported species are also different. However, an attempt has been made to compare values

5 VARSHNEY AND SINGH: ISOPRENE EMISSION FROM INDIAN TREES ACH 24-5 Table 3. A Comparison of Isoprene Emission Rates (mg g 1 h 1 ) Observed in the Present Study With Specific Emission Rate Assigned by Taxonomic Method [Benjamin et al., 1996] Scientific Name P.S. A.R.F. Difference Between P.S. and A.R.F, % A.R.G. Difference Between P.S. and A.R.G, % Heterophragma adenophyllum NA - Kigelia pinnata NA - Mangifera indica NA - Cinnamomum tamala NA - Cinnamomum zeylanicum BDL NA - Syzygium jambolanum NA - Acacia nilotica BDL ND Albizzia lebbeck NA - Pithecelobium dulce NA - Ficus benghalensis 37.0 NA Ficus glomerata 47.6 NA Ficus infectoria 52.0 NA Eucalyptus globulus P.S., present study; A.R.F., assigned rate at family; A.R.G., assigned rate at genus; ND, no difference; NA, not available; BDL, below detection limit. reported in respect of identical species/genus (Table 4). The values obtained in the present study were in reasonable agreement with the literature data (Table 4). Guenther et al. [1991] have reported leaf to leaf and plant to plant variations of about ±50% for isoprene because of the errors/ uncertainties involved in emission measurements due to differences in sample size, sampling and analysis techniques. In view of the above considerations, data reported in the present study and literature values given in tables may be regarded as indicative of the emission characteristics of different plant species. [17] Many of the tree species viz. Albizzia lebbeck, Ceiba petendra, Dalbergia sissoo, Eucalyptus globulus, Ficus benghalensis, Ficus glomerata, Ficus infectoria, Ficus relegiosa, Grevillea robusta, Heterophragma adenophyllum, Kigelia pinnata, Morus alba, Pithecellobium dulce, Pongamia pinnata, Terminalia arjuna and Syzygium jambolanum included in the present study have been preferentially selected for avenue plantation and green belt development in urban and industrial areas in India. Among these, Dalbergia sissoo, Eucalyptus globulus, Ficus benghalensis, Ficus glomerata, Ficus infectoria, Ficus relegiosa, Grevillea robusta, Morus alba, Pithecellobium dulce, Pongamia pinnata, Syzygium jambolanum are high isoprene emitters. Prevalence of high isoprene emitting species in avenue plantations and green belt development has obvious repercussion for urban air quality. The high values of ground level ozone reported for the urban/peri-urban environment of Delhi [Varshney and Aggarwal, 1992; Singh et al., 1997; Varshney and Rout, 1998], appears to be largely on account of wide spread plantations of high VOC emitting tree species in urban areas. In view of the implication of high isoprene emitting species for air quality, it is important that isoprene-emitting potential should also be given serious consideration along with other features while selecting tree species for planting in urban and industrial areas. 4. Summary and Conclusions [18] This study reports, for the first time, measurements of isoprene emission rates of 40 tropical tree species from the Indian subcontinent. The isoprene emission rates (30 C and 1000 mmolm 2 s 1 ) ranged from non-detectable to 81.5 mgg 1 h 1. A large inter-species variation in isoprene emission rate was observed. Among tree species examined, 27.5% were high emitters, 12.5% were moderate emitters, 15% were low emitters, and remaining 45% were BDL/ negligible emitters. [19] Construction of biogenic VOC emission model requires emission factors for each individual species of Table 4. A Comparison Between Isoprene Emission Rates Observed in the Present Study With Values Reported in Literature for Tropical Trees Belonging to Same Species/Genus Scientific Name Present Study Isoprene Emission Rate, mgcg 1 h 1 Scientific Name/Reference Literature Data Isoprene Emission Rate, mgcg 1 h 1 Acacia nilotica BDL Acacia nilotica/harley et al. [2003] BDL Albizzia lebbeck 0.58 Albizzia crass/klinger et al. [2002] <1 Ceiba petendra BDL Ceiba petendra/klinger et al. [1998] BDL Chukresia tabularis BDL Chukresia tabularis/klinger et al. [2002] <1 Dalbergia sissoo Dalbergia fusca/klinger et al. [2002] 70 Dalbergia melanoxylon/klinger et al. [2002] 39.0 Ficus glomerata Ficus stuhlmannii/harley et al. [2003] 31.9 Ficus infectoria Ficus ingens/harley et al. [2003] 74.4 Kigelia pinnata BDL Kigelia africana/harley et al. [2003] BDL Manilkara hexendra BDL Manilkara ochisia/harley et al. [2003] BDL Sterculia alata BDL Sterculia murex/harley et al. [2003] BDL Zizyphus jujuba 1.45 Zizyphus mucronata/guenther et al. [1996] <0.88

6 ACH 24-6 VARSHNEY AND SINGH: ISOPRENE EMISSION FROM INDIAN TREES the landscape. However, it is not feasible to measure emission rate of each and every species particularly in the tropical ecosystem on account of high species diversity. Consequently, actual VOC emission data on many species remains unavailable. To overcome this hurdle, Benjamin et al. [1996] have proposed a method of assigning emission rate on genus and family basis to plant species, for which emission rates are not known. Subsequently, many of the workers have used the taxonomic approach of Benjamin et al. [1996] for assigning emission rates to unexplored species for constructing regional or global emission inventories [Guenther et al., 1994; Geron et al., 1995; Rasmussen and Khalil, 1997]. The results of this study show that emission rate assignment to a particular species at family level may suffer from >50% uncertainty. However, assignment at genus level is relatively more dependable (<50% uncertainty). The measurements reported in this study contribute to the VOC emission database on tropical tree species that will be of help in preparing regional VOC emission inventory. [20] Acknowledgments. A fellowship provided by University Grant Commission, Government of India, New Delhi, to Mr. Abhai Pratap Singh is gratefully acknowledged. References Benjamin, M. T., M. Sudol, L. Bloch, and A. M. Winer, Low-emitting urban forests: A taxonomic methodology for assigning isoprene and monoterpene emission rates, Atmos. Environ., 30, , Chameides, W. L., et al., Ozone precursor relationships in the ambient atmosphere, J. Geophys. Res., 97, , Crutzen, P. J., et al., High spatial and temporal resolution measurements of primary organics and their oxidation products over the tropical forests of Surinam, Atmos. Environ., 34, , Evans, R. C., D. T. Tingey, M. L. Gumpertz, and W. F. Burns, Estimates of isoprene and monoterpenes emission rates in plants, Bot. Gaz., 143, , Fehsenfeld, F., J. Calvert, R. 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7 VARSHNEY AND SINGH: ISOPRENE EMISSION FROM INDIAN TREES ACH 24-7 Tingey, D. T., M. Manning, L. C. Grothaus, and W. F. Burns, The influence of light and temperature on isoprene emission rates from live oak, Plant Phys., 47, , Varshney, C. K., and M. Aggarwal, Ozone pollution in the urban atmosphere of Delhi, Atmos. Environ., 26B, , Varshney, C. K., and C. Rout, Ethylene diurea (EDU) protection against ozone injury in Tomato plants at Delhi, J. Environ. Contamin. Toxico., 61, , Winer, A. M., D. R. Fitz, and P. R. Miller, Investigation of the role of natural hydrocarbons in photochemical smog formation in California, Final Rep. to the Calif. Air Resour. Board, Contract AO , 267 pp, Calif. Air Resour. Board, Riverside, Calif., Winer, A. M., J. Arey, S. M. Aschmann, R. Atkinson, W. D. Long, C. L. Morrison, and O. M. Olszyk, Hydrocarbon emissions from vegetation found in California s Central Valley, Contract A , prepared for California Air Resour. Board, by Statewide Air Pollut. Res. Cent., Riverside, Calif., Winer, A. M., J. Arey, S. M. Aschmann, R. Atkinson, W. D. Long, C. L. Morrison, and O. M. Olszyk, Emission rates of organic compounds from agricultural and natural vegetation found in California Central Valley, Atmos. Environ., 14, , Winer, A. M., J. Karlik, J. Arey, and Y. J. Chung, Biogenic hydrocarbon inventories for California: Generation of essential databases, Final Rep. to the Calif. Air Resour. Board, Contract , Calif. Air Resour. Board, Riverside, Calif., Wuebbles, D., K. Grant, P. Connell, and J. Penner, The role of atmospheric chemistry in climate change, J. Air Poll. Control Ass., 39, 22 28, Zimmerman, P. R., R. B. Chatfield, J. Fishman, P. J. Crutzen, and P. L. Hanst, Estimates on the production of CO and H 2 from the oxidation of hydrocarbon emissions from vegetation, Geophys. Res. Lett., 5, , A. P. Singh and C. K. Varshney, School of Environmental Sciences, Jawaharlal Nehru University, New Delhi , India. (ckvarshney@ hotmail.com)