L. Torres

Diurnal and seasonal course of monoterpene emissions from Quercus ilex (L.) under natural conditions application of light and temperature algorithms

Abstract Quercus ilex is a common oak species in the Mediterranean vegetation and a strong emitter of monoterpenes. Since the short-term control of monoterpene emissions from this species involved both temperature and light, the usual exponential function of temperature may not be sufficient to model the diurnal and seasonal emission course. In the frame of the BEMA-project (Biogenic Emissions in the Mediterranean Area), we investigated the tree-to-tree, branch-to-branch, diurnal, and seasonal variability of monoterpene emissions from Q. ilex over one and a half years at Castelporziano (Rome, Italy). In addition, we checked the suitability of the model developed for isoprene by Guenther et al. (1991, 1993) to simulate the short- and long-term variations of monoterpene emissions from this particular species. We found that the tree-to-tree variability was rather small compared to the experimental error during air sampling acid analysis by diverse laboratories. The branch-to-branch variability was noticeable between sun- and shade-adapted branches only. 80% of total emissions were represented by α-pinene, β-pinene and sabinene, whose proportions were stable over the year and independent of light exposure. The emission factor (emission rate at 30°C and 1000 μmol photon m −2 s −1 ) estimated by the isoprene model or extrapolated from measurements was similar: it was about 22 μg g dw −1 h −1 for sun-exposed branches and 2.3 μg g dw −1 h −1 for shade-adapted branches. It was rather stable over the seasons except during leaf development. The diurnal and seasonal emission patterns from Q. ilex were simulated in a satisfying way by Guenthers algorithms especially if we excluded the laboratory variability. For shade-adapted branches, an emission factor 17 times lower had to be applied, but temperature and light responses were unchanged.

Isolation and preconcentration of volatile organic compounds from water

Abstract Methods for the isolation and/or concentration of volatile organic compounds from water samples for trace organic analysis by gas chromatography are reviewed. The following basic groups of methods are discussed: liquid-liquid extraction, adsorption on solid sorbents, extraction with gas (gas stripping and static and dynamic headspace techniques) and membrane processes. The theoretical bases of these methods are discussed. Experimental arrangements for the isolation and/or concentration of volatile compounds from water are presented and discussed with respect to their efficiency. The applicability of the described methods to the isolation and/or concentration of various organic compounds from waters of various origins is discussed.

Evaluation of the suitability of selected porous polymers for preconcentrations of volatile organic compounds

Abstract Breakthrough volumes on six porous polymers (Chromosorb 101, 103, 107 and Porapak N, Q, T) have been determined for vapours of 25 volatile organic compounds (amines, chlorinated hydrocarbons, etc.). The volumes were determined by a direct method, which seems to be simpler compared to the indirect estimation of breakthrough volume on the basis of such chromatographic parameters as retention volume, number of theoretical plates and peak width. The effect of the concentration of a model compound (acetone) in the gas mixtures on breakthrough volume was also determined on all investigated sorbents. The invetigations were carried out in a specially designed apparatus employing the method of diffusion tubes for the generation of model gaseous mixtures.

Diurnal variation in the concentration of α- and β-pinene in the landes forest (France)

Abstract The study deals with the identification and the determination of the main monoterpenes (α- and β-pinene) released by the pines in the Landes Forest in France. The measurements were taken after preconcentration using TENAX-GC and thermal desorption. The diurnal variation of atmospheric concentration of α- and β-pinene is established; it is less than 0.5 ppbV in the daytime and varies from 2 to 4 ppbV in the night-time. These variations are explained by the fact that the photochemical reactions and the turbulence phenomena to which the terpenes are exposed change quite radically from day to night. The terpene concentration, higher at 5 m than at 25 m, would seem to confirm the existence of a terpene source at ground level.

Estimating the emission of volatile organic compounds (VOC) from the French forest ecosystem

Abstract The present assessment of annual foliar emissions of non-methane volatile organic compounds (VOC) was carried out from a selection of 32 different varieties of trees representing 98% of the French forest. Experimental data were collected over a grid based on the 93 metropolitan departments (national districts). Specific emission potentials and foliar densities were individually assigned to each of the 32 species. Temperatures and light intensities were individually collected for all French departments. As far as possible, the specific emission factors taken into account in the algorithms used for calculating emission were characteristic of species growing in France or nearby. Average monthly and annual emissions of isoprene, monoterpenes and other volatile organic compounds (OVOC) were individually obtained for all departments and for France over the five-year period of the present investigation (1994–1998). The results indicate a periodical annual evolution of average emissions characterized by a rapid growth from March up to a maximum reached in July–August and followed by a net decrease in September–October. The emissions recorded during the months of July and August represent more than 50% of the annual values. Over the whole country, isoprene appears as the most abundant species, with an emission of 457 kt yr −1 , followed by monoterpenes, 350 kt yr √-1 and OVOC, 129 kt yr −1 , such values, respectively, representing 49, 37 and 14% of the total emission. The level of VOC emissions of biogenic origin in France is 50% lower than that of anthropogenic sources. As a whole, the results are affected by a rather large uncertainty, due to the importance of calculated corrective factors, ranged between 4 and 7.

Passive dosimeters — an approach to atmospheric pollutants analysis

Abstract The paper presents a review of the passive methods of sampling of inorganic and organic atmospheric pollutants. The importance of these methods, enabling both evaluation of workplace personal exposure and area monitoring, has been discussed. Commercially available personal monitors, as well as devices under further laboratory investigation have been described. Fundamental theoretical equations describing the operation of both passive devices based on diffusion through an air gap to a layer of collective media and passive devices with permeable membranes have been put forward. Presented and discussed herein are papers dealing with the investigation of the applicability of these devices under laboratory and field conditions, as well as with the comparison of passive monitors with active devices (e.g., detector tubes).

Preconcentration of Atmospheric Terpenes on Solid Sorbents

Abstract Hydrocarbons emitted by vegetation, such as isoprene and monoterpenes, seem to play an important role in atmospheric chemistry. A better estimation of their biogeochemical cycle requires that the levels be testable at any time. The extremely low concentration of these chemicals in the atmosphere necessitates a preconcentration step at the time of smpling. This enrichment was done on 13 solid adsorbents (Tenax GC and TA, Chromosorb 101, 103, 105 and 107, Porapak R and Q, XAD-2, 4 and 7, Ambersorb-XE-340 and Carbosphere). This study allowed us to determine the breakthrough volumes of isoprene and the principal monoterpenes on these adsorbents. Of the adsorbents tested, Tenax GC and TA were those the best adapted to the desorption of compounds as reactive as the terpenes.

Preconcentration and analysis of atmospheric isoprene and monoterpenes System automation

Abstract As part of a study on terpene hydrocarbons in the biosphere-atmosphere exchange processes, an entirely automatic device has been elaborated for sampling, preconcentration and analysis of isoprene and the principal atmospheric monoterpenes. This device comprises mainly a gas chromatograph for analysis and a programmable controller for the management of the operations. It permits measurement of the concentration and flux rate of terpenes. Automatic and continuous cycles (sampling-analysis) were carried out over several days. They were characterized by a reproducibility lower than 1%; their analytical characteristics were quite acceptable.

Monoterpenes in air samples : European intercomparison experiments

Abstract An intercomparison experiment on preconcentration of monoterpenes from air samples was carried out by three European laboratories (Technische Universitat Munchen [TUM], Institut National Polytechnique de Toulouse [INP], Joint Research Center Isprs [JRC]) using Tenax porous polymer as an adsorbent. Sampling procedures, gas chromatographic analysis and standardisation methods differed in each laboratory and were compared in this study. Tenax adsorption tubes loaded with up to 10 monoterpenes (tricyclene, α-pinene, β-pinene, camphene, sabinene, myrcene, δ3-carene, p-cymene, 1,8-cineole and limonene) were created independently and exchanged for analysis between the working groups. For most monoterpenes the recoveries found by the different laboratories were 100%. The precision of analyses was better than 20%. Independent determinations of α-pinene mixing ratios in the air of the crown region in a natural spruce stand corresponded satisfactorily. Monoterpene emission rates of attached twigs in the sun...

Preconcentration of Volatile Sulphur Compounds on Solid Sorbents

Abstract The development of industry and urbanisation is at the origin of ever-increasing levels of anthropogenic pollution. Emissions of sulphur-containing compounds are partly composed of volatile organic compounds which add to those generated through natural processes. For low concentrations, direct assaying is problematic and a preconcentration step is necessary at the time of sampling. In order to select efficient solid sorbents for use in preconcentration of volatile organic sulphur-containing compounds, the breakthrough volumes of a certain number of mercaptans and sulphides have been determined on 9 porous polymers (Chromosorb 101, 103, 107,—Porapak Q, T, N,—XAD-4, XAD-7 and Tenax G.C.) and on Carbosphere. The breakthrough volumes were determined using a direct method with an apparatus based on diffusion tubes dynamically generating standard mixtures of carrier gas and sulphur-containing compounds.