C. Boissard

Screening of 18 Mediterranean plant species for volatile organic compound emissions

Abstract Eighteen tree and shrub species were screened for emissions of isoprene and other volatile organic compounds (VOCs) at three locations at Castelporziano (Italy) using a bag-enclosure sampling method followed by GC analysis. Thirty emitted compounds were identified. Temperature sensitivity of emissions of monoterpenes varied between species. Strong temperature dependencies were found for isoprene emissions. For monoterpene-emitting plant species with greatest ground cover in the dunes and macchia habitats, α-pinene, β-pinene and sabinene appeared to be the most frequently and abundantly emitted compounds. Isoprene was the major emission from the shrub species screened in the forest. Emissions from four dominant plant species were scaled up to estimate total fluxes from the dunes and macchia over a daytime period. Species with greatest biomass but low emission rates made a substantial contribution to total emissions.

Volatile organic compounds (VOCs) emitted from 40 Mediterranean plant species : VOC speciation and extrapolation to habitat scale

Forty native Mediterranean plant species were screened for emissions of the C5 and C10 hydrocarbons, isoprene and monoterpenes, in five different habitats. A total of 32 compounds were observed in the emissions from these plants. The number of compounds emitted by different plant species varied from 19 (Quercus ilex) to a single compound emission, usually of isoprene. Emission rates were normalised to generate emission factors for each plant species for each sampling event at standard conditions of temperature and light intensity. Plant species were categorised according to their main emitted compound, the major groups being isoprene, α-pinene, linalool, and limonene emitters. Estimates of habitat fluxes for each emitted compound were derived from the contributing plant species’ emission factors, biomass and ground cover. Emissions of individual compounds ranged from 0.002 to 505 g ha−1 h−1 (camphene from garrigue in Spain in autumn and isoprene from riverside habitats in Spain in late spring; respectively). Emissions of isoprene ranged from 0.3 to 505 g ha−1 h−1 (macchia in Italy in late spring and autumn; and riverside in Spain in late spring; respectively) and α-pinene emissions ranged from 0.51 to 52.92 g ha−1 h−1 (garrigue in Spain in late spring; and forest in France in autumn; respectively). Habitat fluxes of most compounds in autumn were greater than in late spring, dominated by emissions from Quercus ilex, Genista scorpius and Quercus pubescens. This study contributes to regional emission inventories and will be of use to tropospheric chemical modellers.

Effect of habitat and age on variations in volatile organic compound (VOC) emissions from Quercus ilex and Pinus pinea

A dynamic branch enclosure was used to measure emission rates of volatile organic compounds (VOCs) under field conditions from two common native Mediterranean species, Quercus ilex and Pinus pinea. In addition to α-pinene, β-pinene, sabinene, limonene and cineole, a suite of lesser known compounds were tentatively identified including cis- and trans-ocimene, cis- and trans-linalool oxide and sabinaketone. Emissions of isoprene from Quercus ilex were insignificant in comparison to those of the monoterpenes and were not detected from Pinus pinea. Variability in emission rates between two habitats, the forest and the dunes, were assessed for Quercus ilex. Temperature sensitivities of emissions and total summed emission rates from Quercus ilex were clearly related to environmental conditions. Emission rates from Pinus pinea showed great variability, but differences between normalised mean emission rates from mature forest and young plantation trees may be significant. Existing emission rate models were found to inadequately describe the observed data.

Field studies of isoprene emissions from vegetation in the northwest Mediterranean region

During the Biogenic Emissions in the Mediterranean Area (BEMA) project field campaigns (1993 - 1997), 40 native Mediterranean plant species were screened for emissions of isoprene and monoterpenes using a branch enclosure sampling method with subsequent gas chromatographic-flame ionization detector (GC-FID) and GC-mass selective detector (MS) analysis. Thirteen species emitted more than 0.5 μg (C) g−1 dw h−1 isoprene at 30°C and 1000 μmol m−2 s−1 photosynthetically active radiation (PAR), of which nine species emitted more than 20 μg (C) g−1 dw h−1. Emissions of isoprene were strongly correlated with temperature and PAR, and were reasonably well predicted by existing algorithms. There was little intraspecies and day to day variation in base emission rates. In general, median base emission rates were higher in summer compared to autumn for most species. Significant difference in aggregated habitat base emission rates was found between dunes, garrigue, woodland, and riverside sample sites. Although considerable unexplained variability in base emission rates remains to be explored, first estimates of base emission rates for Mediterranean shrublands are presented here.

Biogenic emissions of volatile organic compounds from gorse (Ulex europaeus): Diurnal emission fluxes at Kelling Heath, England

Volatile organic compound (VOC) emission fluxes from Gorse (Ulex europaeus) were measured during May 30–31, 1995 at Kelling Heath in eastern England by using bag enclosure and gradient methods simultaneously. The enclosure measurements were made from branches at different stages of physiological development (flowering, after flowering, and mixed). Isoprene was found to represent 90% of the total VOC emissions, and its emission rates fluctuated from 6 ng (g dwt)−1 h−1 in the early morning to about 9700 ng(g dwt)−1 h−1 at midday. Averaged emission rates standardized to 20°C were 1625, 2120, and 3700 ng (g dwt)−1 h−1 for the new grown, “mixed,” and flowering branch, respectively. Trans-ocimene and α-pinene were the main monoterpenes emitted and represented, on average, 47.6% and 36.9% of the total monoterpenes. Other monoterpenes, camphene, sabinene, β-pinene, myrcene, limonene and γ-terpinene, were positively identified but together represented less than 1.5% of the total VOC emissions from gorse. Maximum isoprene concentrations in air at the site were measured around midday at 2 m (174 parts per trillion by volume, or pptv) and 6 m (149 pptv), and minimum concentrations were measured during the night (8 pptv at both heights). Mean daytime α-pinene air concentrations of 141 and 60 pptv at 2 and 6 m height were determined, but trans-ocimene concentrations were less than the analytical detection limit (4 pptv), suggesting rapid chemical removal of this compound from air. The isoprene fluxes calculated by the micrometeorological gradient method showed a pattern similar to that of those calculated by the enclosure method, with isoprene emission rates maximum at midday (100 μg m−2 h−1) and not detectable during the nighttime. Assessment of the fraction of the site covered by gorse plants enabled an extrapolation of emission fluxes from the enclosure measurements. When averaged over the 2 day experiment, isoprene fluxes of 29.8 and 27.8 μg m−2 h−1 were obtained from the gradient and the enclosure extrapolation respectively. These isoprene fluxes to the atmosphere represented between 0.12% and 0.35% of the net assimilated carbon (as CO2) uptake rate for gorse.

Measurement of carbon dioxide and hydrocarbon fluxes from a sitka spruce forest using micrometeorological techniques

CO2 and hydrocarbon fluxes from a sitka spruce forest were measured using a conditional sampling method, The method was used in two ways: (1) an automated system was used to monitor continuously the mixing ratio difference of total hydrocarbons and CO2 in sampling lines for updraught and downdraught air and (2) conditionally sampled updraught and downdraught air was passed through adsorption tubes, which subsequently were analyzed in the laboratory, to determine the fluxes of nonmethane hydrocarbons (NMHCs), Aerodynamic gradient measurements of NMHC fluxes were made over the same period. Method (1) produced a high temporal resolution data set of approximately 4 days of near-continuous fluxes. Marked diurnal trends in CO2 flux were evident. Peak daylight photosynthetic fluxes ranged from -30 to -90 mmol m(-2) h(-1). Smaller fluxes were noted during heavy rainfall and diminished photosynthetically active radiation, Nighttime respiration ranged from 0 to 10 mmol m(-2) h(-1). Total hydrocarbon fluxes were 3 orders of magnitude smaller. During hot, sunny conditions a total hydrocarbon flux of approximately 400 mu mol m(-2) h(-1) (CH4 equivalents) was observed, Fluxes of specific NMHC compounds, from method (2), ranged between 90 and 563 mu g m(-2) hour(-1). The annual carbon flux to Great Britains conifer forests was estimated to be 1.3 Mt using a simple upscaling model based on the observations of CO2 flux during the field experiment.

Emissions of VOCs from stressed and unstressed vegetation.

During 1989–1994 the emission rates of VOCs (primarily isoprene and monoterpenes) from various plant species were assessed by different sampling methods, including the use of excised plant material (leaf disc method) and a dynamic flowthrough branch enclosure, developed during the course of this work. Both stressed and unstressed plants have been studied.