Isoprene Emission Potential Research Articles

Characteristics of isoprene emission from moso bamboo leaves in a forest in central Taiwan

The expansion of moso bamboo (Phyllostachys edulis) may potentially impact regional isoprene emissions. Modeling based on field measurements is an effective approach for assessing the potential impact of the moso bamboo expansion. The G93 algorithm is one of the most widely used models, however no studies have tested the applicability of the algorithm for moso bamboo isoprene emission. This study was undertaken to establish a model for reproducing moso bamboo isoprene emission fluxes. To this aim, this study examined 1) the isoprene emission ability of moso bamboo, and 2) its responses to environmental factors such as leaf temperature and light. We also tested 3) the reproducibility of the G93 algorithm for moso bamboo isoprene emission fluxes. This study used a chamber method with a modified photosynthesis system and carbon absorbents to quantify isoprene emitted from bamboo leaves in central Taiwan under the humid subtropical climate. First, we screened isoprene emission from 12 bamboo species, and the results confirmed that moso bamboo exhibited significant isoprene emission potential. Second, we measured isoprene emission fluxes from moso bamboo leaves with light controls every month from summer to spring. The isoprene emission fluxes increased with photosynthetic photon flux density (PPFD); under sufficient PPFD conditions, the seasonal changes in the isoprene emission fluxes were regulated by leaf temperature, and low isoprene emission fluxes were found in low leaf temperature conditions. Thirdly, overestimations were observed in the G93 algorithm with the original parameters in periods with leaf temperatures <23 °C. Using the G93 algorithm with site-specific parameters could improve the overestimation in the low-temperature period. This study suggests the necessity of parameterization in the G93 algorithm to reproduce the suppression of isoprene emission fluxes from moso bamboo leaves in the low-temperature period.

Isoprene emission potentials from European oak forests derived from canopy flux measurements: an assessment of uncertainties and inter-algorithm variability

Abstract. Biogenic emission algorithms predict that oak forests account for ∼ 70 % of the total European isoprene budget. Yet the isoprene emission potentials (IEPs) that underpin these model estimates are calculated from a very limited number of leaf-level observations and hence are highly uncertain. Increasingly, micrometeorological techniques such as eddy covariance are used to measure whole-canopy fluxes directly, from which isoprene emission potentials can be calculated. Here, we review five observational datasets of isoprene fluxes from a range of oak forests in the UK, Italy and France. We outline procedures to correct the measured net fluxes for losses from deposition and chemical flux divergence, which were found to be on the order of 5–8 and 4–5 %, respectively. The corrected observational data were used to derive isoprene emission potentials at each site in a two-step process. Firstly, six commonly used emission algorithms were inverted to back out time series of isoprene emission potential, and then an average isoprene emission potential was calculated for each site with an associated uncertainty. We used these data to assess how the derived emission potentials change depending upon the specific emission algorithm used and, importantly, on the particular approach adopted to derive an average site-specific emission potential. Our results show that isoprene emission potentials can vary by up to a factor of 4 depending on the specific algorithm used and whether or not it is used in a big-leaf or canopy environment (CE) model format. When using the same algorithm, the calculated average isoprene emission potential was found to vary by as much as 34 % depending on how the average was derived. Using a consistent approach with version 2.1 of the Model for Emissions of Gases and Aerosols from Nature (MEGAN), we derive new ecosystem-scale isoprene emission potentials for the five measurement sites: Alice Holt, UK (10 500 ± 2500 µg m−2 h−1); Bosco Fontana, Italy (1610 ± 420 µg m−2 h−1); Castelporziano, Italy (121 ± 15 µg m−2 h−1); Ispra, Italy (7590 ± 1070 µg m−2 h−1); and the Observatoire de Haute Provence, France (7990 ± 1010 µg m−2 h−1). Ecosystem-scale isoprene emission potentials were then extrapolated to the leaf-level and compared to previous leaf-level measurements for Quercus robur and Quercus pubescens, two species thought to account for 50 % of the total European isoprene budget. The literature values agreed closely with emission potentials calculated using the G93 algorithm, which were 85 ± 75 and 78 ± 25 µg g−1 h−1 for Q. robur and Q. pubescens, respectively. By contrast, emission potentials calculated using the G06 algorithm, the same algorithm used in a previous study to derive the European budget, were significantly lower, which we attribute to the influence of past light and temperature conditions. Adopting these new G06 specific emission potentials for Q. robur (55 ± 24 µg g−1 h−1) and Q. pubescens (47 ± 16 µg g−1 h−1) reduced the projected European budget by ∼ 17 %. Our findings demonstrate that calculated isoprene emission potentials vary considerably depending upon the specific approach used in their calculation. Therefore, it is our recommendation that the community now adopt a standardised approach to the way in which micrometeorological flux measurements are corrected and used to derive isoprene, and other biogenic volatile organic compounds, emission potentials.

Photosynthesis-dependent isoprene emission from leaf to planet in a global carbon-chemistry-climate model

Abstract. We describe the implementation of a biochemical model of isoprene emission that depends on the electron requirement for isoprene synthesis into the Farquhar–Ball–Berry leaf model of photosynthesis and stomatal conductance that is embedded within a global chemistry-climate simulation framework. The isoprene production is calculated as a function of electron transport-limited photosynthesis, intercellular and atmospheric carbon dioxide concentration, and canopy temperature. The vegetation biophysics module computes the photosynthetic uptake of carbon dioxide coupled with the transpiration of water vapor and the isoprene emission rate at the 30 min physical integration time step of the global chemistry-climate model. In the model, the rate of carbon assimilation provides the dominant control on isoprene emission variability over canopy temperature. A control simulation representative of the present-day climatic state that uses 8 plant functional types (PFTs), prescribed phenology and generic PFT-specific isoprene emission potentials (fraction of electrons available for isoprene synthesis) reproduces 50% of the variability across different ecosystems and seasons in a global database of 28 measured campaign-average fluxes. Compared to time-varying isoprene flux measurements at 9 select sites, the model authentically captures the observed variability in the 30 min average diurnal cycle (R2 = 64–96%) and simulates the flux magnitude to within a factor of 2. The control run yields a global isoprene source strength of 451 TgC yr−1 that increases by 30% in the artificial absence of plant water stress and by 55% for potential natural vegetation.

Isoprene function in two contrasting poplars under salt and sunflecks

In the present study, biogenic volatile organic compound (BVOC) emissions and photosynthetic gas exchange of salt-sensitive (Populus x canescens (Aiton) Sm.) and salt-tolerant (Populus euphratica Oliv.) isoprene-emitting and non-isoprene-emitting poplars were examined under controlled high-salinity and high-temperature and -light episode ('sunfleck') treatments. Combined treatment with salt and sunflecks led to an increased isoprene emission capacity in both poplar species, although the photosynthetic performance of P. × canescens was reduced. Indeed, different allocations of isoprene precursors between the cytosol and the chloroplast in the two species were uncovered by means of (13)CO2 labeling. Populus × canescens leaves, moreover, increased their use of 'alternative' carbon (C) sources in comparison with recently fixed C for isoprene biosynthesis under salinity. Our studies show, however, that isoprene itself does not have a function in poplar survival under salt stress: the non-isoprene-emitting leaves showed only a slightly decreased photosynthetic performance compared with wild type under salt treatment. Lipid composition analysis revealed differences in the double bond index between the isoprene-emitting and non-isoprene-emitting poplars. Four clear metabolomics patterns were recognized, reflecting systemic changes in flavonoids, sterols and C fixation metabolites due to the lack/presence of isoprene and the absence/presence of salt stress. The studies were complemented by long-term temperature stress experiments, which revealed the thermotolerance role of isoprene as the non-isoprene-emitting leaves collapsed under high temperature, releasing a burst of BVOCs. Engineered plants with a low isoprene emission potential might therefore not be capable of resisting high-temperature episodes.

Isoprene in poplar emissions: effects on new particle formation and OH concentrations

Abstract. Stress-induced volatile organic compound (VOC) emissions from transgenic Grey poplar modified in isoprene emission potential were used for the investigation of photochemical secondary organic aerosol (SOA) formation. In poplar, acute ozone stress induces the emission of a wide array of VOCs dominated by sesquiterpenes and aromatic VOCs. Constitutive light-dependent emission of isoprene ranged between 66 nmol m−2 s−1 in non-transgenic controls (wild type WT) and nearly zero (&lt;0.5 nmol m−2 s−1) in isoprene emission-repressed plants (line RA22), respectively. Nucleation rates of up to 3600 cm−3 s−1 were observed in our experiments. In the presence of isoprene new particle formation was suppressed compared to non-isoprene containing VOC mixtures. Compared to isoprene/monoterpene systems emitted from other plants the suppression of nucleation by isoprene was less effective for the VOC mixture emitted from stressed poplar. This is explained by the observed high efficiency of new particle formation for emissions from stressed poplar. Direct measurements of OH in the reaction chamber revealed that the steady state concentration of OH is lower in the presence of isoprene than in the absence of isoprene, supporting the hypothesis that isoprenes' suppressing effect on nucleation is related to radical chemistry. In order to test whether isoprene contributes to SOA mass formation, fully deuterated isoprene (C5D8) was added to the stress-induced emission profile of an isoprene free poplar mutant. Mass spectral analysis showed that, despite the isoprene-induced suppression of particle formation, fractions of deuterated isoprene were incorporated into the SOA. A fractional mass yield of 2.3% of isoprene was observed. Future emission changes due to land use and climate change may therefore affect both gas phase oxidation capacity and new particle number formation.

High within‐canopy variation in isoprene emission potentials in temperate trees: Implications for predicting canopy‐scale isoprene fluxes

Isoprene emission potential (ES) varies in tree canopies, and such variations have potentially major implications for predicting canopy level emissions. So far, quantitative relationships of ES with irradiance are missing, and interspecific variation in ES plasticity and potential effects on canopy level emissions have not been characterized. ES, foliage structural, chemical, and photosynthetic characteristics were studied relative to integrated within‐canopy daily quantum flux density (Qint) in temperate deciduous tree species Quercus robur, Populus tremula, Salix alba, and Salix caprea, and canopy isoprene emissions were calculated considering observed variation in ES and under different simplifying assumptions. Strong positive curvilinear relationships between nitrogen and dry mass per unit area, photosynthetic potentials and ES per area with Qint were observed. Structural, chemical, and photosynthetic traits varied 1.5‐fold to 4‐fold and ES per area 3‐fold to 27‐fold within the canopy. ES variation reflected accumulation of mesophyll cell layers and greater emission capacity of average cells. Species with largest structural and photosynthetic plasticity had greatest plasticity in ES. Relative to the simulation considering within‐canopy variation in ES, the bias from assuming a constant ES varied between −8% and +68%, and it scaled positively with ES plasticity. The bias of big‐leaf simulations varied between −22% and −35%, and it scaled negatively with ES plasticity. A generalized canopy response function of ES developed for all species resulted in the lowest bias between −11% and 6% and can be recommended for practical applications. The results highlight huge within‐canopy and interspecific variation in ES and demonstrate that ignoring these variations strongly biases canopy emission predictions.

A model for European Biogenic Volatile Organic Compound emissions: Software development and first validation

A grid-oriented Biogenic Emission Model (BEM) has been developed to calculate Non-Methane Volatile Organic Compound (NMVOC) emissions from vegetation in high spatial and temporal resolutions. The model allows the emissions calculation for any modeling domain covering Europe on the basis of: 1) the U.S. Geological Survey 1-km resolution land-use database, 2) a land-use specific, monthly isoprene, monoterpene and Other Volatile Organic Compound (OVOC) emission potentials and foliar biomass densities database, 3) temperature and solar radiation data provided by the mesoscale meteorological model MM5. The model was applied for Europe in 30-km spatial resolution for the year 2003. The European total emissions for 2003 consist of 33.0% isoprene, 25.5% monoterpenes and 41.5% OVOC. BEM results are compared with those from the well-documented global Model of Emissions of Gases and Aerosols from Nature (MEGAN). The BEM total emissions compare well with the MEGAN ones. In July 2003, the results of both models agree within a factor of 1.2 for total isoprene emissions and within a factor of 2 for total monoterpene emissions. The comparison of the spatial distributions of the July 2003 isoprene and monoterpene emissions calculated with BEM and MEGAN shows that, in the greater part of the study area, the differences are below the current uncertainty limit for the estimation of spatially-resolved biogenic VOC emissions in Europe being equal to about ±600 kg km −2 month −1. Differences that are above this limit are found mainly in the eastern European countries for isoprene and in the Mediterranean countries for monoterpenes.

Analysis of 1-deoxy- d-xylulose 5-phosphate synthase activity in Grey poplar leaves using isotope ratio mass spectrometry

Deoxy-xylulose phosphate synthase (DXS) catalyzes the first step of the methylerythritol phosphate (MEP) pathway and it might regulate the metabolic flux in plastidic isoprenoid biosynthesis. We developed a sensitive assay suitable for plant extracts that is based on the decarboxylation of labeled pyruvate (1- 13C)-PYR and detection of 13CO 2 by isotope ratio mass spectrometry. We tested our method investigating the DXS activity in poplar leaves. Apparent DXS activity showed Michaelis constants of 111 and 158 μM for glyceraldehyde phosphate and pyruvate, respectively; pH and temperature optima were found at pH 8.6 and 45 °C. DXS activity was inhibited when the competitive inhibitor β-fluoropyruvate was added to the reaction mixture. DXS activity strongly depended on leaf development with higher activity in young leaves and correlated fairly well with leaf isoprene emission potential. In mature poplar leaves, isoprene emission is the main metabolic sink of plastidic isoprenoid intermediates. Consequently, we found lower DXS activity in non-isoprene-emitting lines of poplar than in emitting plants as indicator of a lower demand of metabolic flux within the MEP pathway.

A biogenic volatile organic compound emission inventory for Hong Kong

Biogenic volatile organic compounds (BVOCs) in the atmosphere react to form ozone and secondary organic aerosols, which deteriorate air quality, affect human health, and indirectly influence global climate changes. The present study aims to provide a preliminary assessment of BVOC emissions in Hong Kong (HKSAR). Thriteen local tree species were measured for their isoprene emission potential. Tree distribution was estimated for country park areas based on field survey data. Plant emission data obtained from measurements and the literature, tree distribution estimation data, land use information, and meteorological data were combined to estimate annual BVOC emissions of 8.6×10 9 g C for Hong Kong. Isoprene, monoterpenes, and other VOCs contributed about 30%, 40%, and 30% of the estimated total annual emissions, respectively. Although hundreds of plant species are found in Hong Kong country parks, the model results indicate that only 10 tree species contribute about 76% of total annual VOC emissions. Prominent seasonal and diurnal variations in emissions were also predicted by the model. The present study lays a solid foundation for future local research, and results can be applied for studying BVOC emissions in nearby southern China and Asian regions that share similar climate and plant distributions.

Monoterpene and isoprene emissions from typical tree species in forests around Mexico City

The isoprenoid emission of sacred fir ( Abies religiosa (Kunth) Schltdl. & Cham.), patula pine ( Pinus patula Schiede, Schltdl. & Cham.) and net-leaf oak ( Quercus rugosa Née) was investigated in Mexico City during the years 2002 and 2003. Chemical compound specific emission factors were obtained for different months of the year. Net-leaf oak is an isoprene emitter whereas the other tree species emit monoterpenes. α -Pinene and linalool are the main compounds emitted from sacred fir and patula pine, respectively. In general, the emission of monoterpenes is temperature dependent, whereas α -pinene emission of sacred fir is controlled by light and temperature like the isoprene emission of net-leaf oak. All isoprenoids show a strong seasonality which is plant species specific. Emission factors for the conifers were high in October and low in April (sacred fir: 6.07 μ g C g - 1 dw h - 1 in October and 0.02 μ g C g - 1 dw h - 1 in April; patula pine: 4.22 μ g C g - 1 dw h - 1 in October and 1.13 μ g C g - 1 dw h - 1 in June). Isoprene emission potential of net-leaf oak was very variable in the different seasons with low source strengths in July (rainy season: 1.19 μ g C g - 1 dw h - 1 ) and November (cold/dry season: 18.50 μ g C g - 1 dw h - 1 ) but high in May (warm/dry season: 66.27 μ g C g - 1 dw h - 1 ). The results indicate that present biogenic emission inventories of the Mexico City area have to be revised by using the new emission factors of native tree species including the seasonal impact.

A highly spatially and temporally resolved inventory for biogenic isoprene and monoterpene emissions: Model description and application to Great Britain

An inventory describing the fluxes of the volatile organic compound (VOC), isoprene, and the class of VOCs, the monoterpenes, from the biosphere to the atmosphere has been constructed for Great Britain (GB). The controlling parameters were emission potentials from individual plant species, plant species distribution, biomass distribution, temperature, and light intensity. Species distribution and cover data from a national survey of vegetation in 1990 were used. A database of monthly biomass factors was compiled and a qualitative database of VOC emission potentials from vegetation species was updated to a quantitative form. This was used in conjunction with a taxonomic methodology to assign isoprene and monoterpene emission potentials to each plant species extant in GB. Hourly meteorological data for 1998 were calculated using a three‐dimensional nonhydrostatic meteorological mesoscale model (MM5) and these were used to predict the isoprene and monoterpene fluxes in GB in 1998 on a spatial scale of 12 × 12 km and with an hourly temporal resolution. Estimates of annual biogenic isoprene and monoterpene fluxes were 8 and 83 kt, respectively, for the model year. Picea sitchensis (Sitka spruce) is the dominant emitting species in GB, emitting approximately 40% of the annual isoprene and monoterpene fluxes. The dominant emitting regions in GB are coniferous forests in Scotland (isoprene and monoterpenes) and a Populus spp. (poplar) rich area in eastern England (isoprene). Overall uncertainty in the estimates is a maximum of a factor of 4. A sensitivity analysis of the model was used to study the impact of changes in vegetation cover and climate on VOC emission.

Seasonal variation of VOC concentrations above a boreal coniferous forest

Biogenic volatile organic compound (VOC) concentrations in ambient air were measured in Central Finland from April 2000 to April 2002. The concentrations of isoprene increased in May and declined in September, but the concentrations of its oxidation products, methacrolein and methyl vinyl ketone, remained at about 100 ppt level also after that suggesting they might have anthropogenic sources as well. The winter and summer mean midday concentrations of monoterpenes were 97 and 250 pptv, respectively. The winter concentrations of monoterpenes were unexpectedly high, but they can be explained by small, but existing, emissions from at least Picea abies and also by the much longer atmospheric lifetime of monoterpenes in winter than in summer. The hydroxyl and nitrate radical concentrations in Central Finland were calculated for the year 2000 using an observationally constrained photochemical box model. Using the calculated hydroxyl radical concentrations the atmospheric lifetime of α-pinene with respect to the OH reaction was estimated to be 50 times longer in December than in July. The nitrate and ozone reactions extend the atmospheric lifetime of α-pinene to 3–4 fold in winter in comparison with the summer lifetime. The mean afternoon (12–4 p.m.) emission potentials (at 30°C according to Guenther et al., J. Geophys. Res. 98 (1993) 12609) were 0.4, 0.2, 1.4, 0.7, 0.4, and 0.2 μg g −1 dry weight h −1 in January, April, May, June, July, and October, respectively. In summer the VOC emissions also included isoprene and sesquiterpenes. The highest isoprene emission potential was observed in June (1.3 μg g −1 dry weight h −1, (at T=30°C and PPFD=1000 μmol m −2 s −1 according to Guenther et al.) and the highest sesquiterpene emission potential in July (0.6 μg g −1 dry weight h −1, scaled to 30°C similarly to the monoterpenes).

Temporal variability in basal isoprene emission factor.

Seasonal variability in basal isoprene emission factor (&mgr;g C g(-1) h(-1) or nmol m(-2) s(-1), leaf temperature at 30 degrees C and photosynthetically active radiation (PAR) at 1000 &mgr;mol m(-2) s(-1)) was studied during the 1998 growing season at Duke Forest in the North Carolina Piedmont. Emissions from eight upper-canopy white oak (Quercus alba L.) leaves were measured periodically from the onset of isoprene emission on Day of Year (DOY) 119 (April 29) to leaf senescence in late October (DOY 299). Emissions from four leaves were measured under basal conditions with a controlled-environment cuvette system equipped with 10-ml gas-tight syringes and a reduction gas detector. Emissions from the other four leaves were measured under ambient conditions with the same system. Emission rates from the four leaves measured under ambient conditions were adjusted to basal conditions based on the PAR and leaf temperature algorithms of Guenther et al. (1993). The seasonal onset of isoprene emission was in agreement with previous studies where cumulative degree days from the date of the last spring frost were used to estimate bud break, leaf expansion, and increase in basal emission factor (EF). Between DOY 141 (May 21) and 240 (August 28), mean meteorological conditions 6 to 18 h prior to the EF measurements (ambient PAR and temperature) explained up to 78% of the variability in mean basal EF between measurement periods. Summertime mean isoprene emission potential was reached on DOY 141 (May 21) and was maintained until DOY 240 (August 28), when isoprene emission began to decline monotonically as leaf senescence approached. The mean value for leaves measured under ambient conditions and adjusted to basal conditions for DOY 141-240 was 75.6 &mgr;g C g(-1) h(-1) (74.2-79.1), whereas the mean value for leaves measured under basal conditions was 72.9 &mgr;g C g(-1) h(-1) (64.7-88.9). Between DOY 141 and 240, daily mean isoprene EFs varied from 54 to 96 &mgr;g C g(-1) h(-1) (27 to 49 nmol m(-2) s(-1)). In agreement with previous work at this and other sites, basal isoprene emission rates of fully exposed leaves at the crown apex of this tree were about 20% higher than those of the selected leaves. The length of the period prior to measurement of isoprene emission, during which meteorology was correlated with basal EF, appeared to be related to the timing and periodicity of meteorological change, and probably explains quantitative differences in the length of this period among studies. The empirical equation that we derived for this effect explained variability in midday EFs at the study site, but its general applicability remains to be tested. Strong diurnal changes in EF (as high as a factor of 2) are implied in this study, and should be examined further.

Isoprene synthase activity and its relation to isoprene emission in Quercus robur L. leaves

Pedunculate oak (Quercus robur L.) is known as a strong isoprene (2‐methyl‐1,3‐butadiene) emitter. Diurnal changes in isoprene emission were determined by branch enclosure measurements. In contrast to the diurnal cycle in emission rates, specific isoprene synthase activity in the leaves remained unchanged. Based on in vitro enzyme activity and its temperature dependency, an isoprene synthesis capacity at specific leaf temperatures was calculated. The comparison of these ‘leaf temperature‐dependent enzyme capacities’ and the measured emission rates revealed that the enzyme activity of isoprene synthase is comparable to the observed isoprene emission rates. In addition, variation in the isoprene synthase activity of the leaves due to changes in light intensity during leaf development was investigated. A 50% reduction of light intensity by shading of single branches reduced isoprene synthase activity by ≈ 60% compared with full sunlight. The calculation of isoprene synthesis capacities based on enzymatic data obtained under optimum reaction conditions, corrected for actual leaf temperature and related to leaf surface area, provides a sound basis for predicting the isoprene emission potential of plants.