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RESUMO Foram padronizados os graus de lesões dos sacos aéreos em perus com aerossaculite, associadas com a presença de isolados de enterobactérias nesses órgãos. Um total de 110 amostras de sacos aéreos de perus machos com aerossaculite foi coletado para o estudo. Durante o processo de abate, as amostras foram coletadas por meio de swabs e submetidas a três métodos de armazenamento (imediato, congelado ou pré-incubado após congelamento) para posterior comparação das suas eficiências de isolamento. Os gêneros da família Enterobacteriaceae foram identificados pelas séries bioquímicas EPM, MILi e citrato de Simmons. O crescimento bacteriano ocorreu em 43,64% das amostras. Neste estudo, quatro padrões de lesões de aerossaculite foram identificados de acordo com as características patológicas dos sacos aéreos. Os principais gêneros de enterobactérias identificadas foram: Escherichia coli, Citrobacter, Proteus, Edwardsiella, Morganella, Kluyvera, Salmonella e Klebsiella. Foi observado que os graus padronizados como 3 e 4 apresentaram maior variedade de gêneros bacterianos. O armazenamento imediato apresentou maior porcentagem de positividade, 41,82%, no entanto o pré-incubado após congelamento se apresentou mais eficaz em relação à quantidade de colônias. ABSTRACT The degrees of air sac lesions in turkeys with airsacculitis were standardized, associated with the presence of Enterobacteriaceae isolated from these organs. A total of 110 samples of air sacs from male turkeys with airsacculitis were collected and analyzed. During the slaughtering process, the sample collection was done using swabs and submitted to three storage methods (immediate, frozen, or pre incubated after freezing) for further comparison of their isolated efficiency. The bacterial genera of the family Enterobacteriaceae were identified biochemical series EPM, MILi and Simmons citrate. Bacterial growth occurred in 43.64% of samples. In this study, four patterns of aerossaculitis lesions were identified according to the pathological characteristics of air sacs. The frequencies of the Enterobacteriaceae isolated identified in the samples were: Escherichia coli, Citrobacter, Proteus, Edwardsiella, Morganell, Kluyvera, Salmonella and Klebsiella. Otherwise, it was observed that the levels already standardized as level three and four showed higher variety of genus. The immediate storage showed higher percentage of positivity at 41.82%, however, the pre incubated after freezing showed more efficiency in relation to the quantity of colonies.

Emissions of Biogenic Volatile Organic Compounds (BVOCs) observed during 2007 from an experimental Pinus taeda plantation in Central North Carolina are compared with model estimates from the Model of Emissions of Gases and Aerosols from Nature (MEGAN) version 2.1. Relaxed eddy accumulation (REA) estimates of 2-methyl-3-buten-2-ol (MBO) fluxes are a factor of 3-4 higher than MEGAN estimates. MEGAN monoterpene emission estimates were a factor of approximately two higher than REA flux measurements. MEGAN β-caryophyllene emission estimates were within 60% of growing season REA flux estimates but were several times higher than REA fluxes during cooler, dormant season periods. The sum of other sesquiterpene emissions estimated by MEGAN was several times higher than REA estimates throughout the year. Model components are examined to understand these discrepancies. Measured summertime leaf area index (LAI) (and therefore foliar biomass) is a factor of two higher than assumed in MEGAN for the P. taeda default. Increasing the canopy mean MBO emission factor from 0.35 to 1.0mgm(-2)h(-1) also reduces MEGAN vs. REA flux differences. This increase is within current MBO emission factor uncertainties. The algorithm within MEGAN which adjusts isoprene emission estimates as a function of the temperature and light of the previous 24h seems also to improve the seasonal MEGAN MBO correlation with REA fluxes. Including the effects of the previous 240h, however, seems to degrade temporal model correlation with fluxes. Monoterpene and sesquiterpene composition data from the REA are compared with MEGAN2.1 estimates and also branch enclosure and needle extract data collected at this site. To our knowledge, the flux data presented here are the first reported for MBO and sesquiterpenes from a P. taeda ecosystem.

MONTES (>Woodlands>) was a multidisciplinary international field campaign aimed at measuring energy, water and especially gas exchange between vegetation and atmosphere in a gradient from short semi-desertic shrublands to tall wet temperate forests in NE Spain in the North Western Mediterranean Basin (WMB). The measurements were performed at a semidesertic area (Monegros), at a coastal Mediterranean shrubland area (Garraf), at a typical Mediterranean holm oak forest area (Prades) and at a wet temperate beech forest (Montseny) during spring (April 2010) under optimal plant physiological conditions in driest-warmest sites and during summer (July 2010) with drought and heat stresses in the driest-warmest sites and optimal conditions in the wettest-coolest site. The objective of this campaign was to study the differences in gas, water and energy exchange occurring at different vegetation coverages and biomasses. Particular attention was devoted to quantitatively understand the exchange of biogenic volatile organic compounds (BVOCs) because of their biological and environmental effects in the WMB. A wide range of instruments (GC-MS, PTR-MS, meteorological sensors, O3 monitors,. .) and vertical platforms such as masts, tethered balloons and aircraft were used to characterize the gas, water and energy exchange at increasing footprint areas by measuring vertical profiles. In this paper we provide an overview of the MONTES campaign: the objectives, the characterization of the biomass and gas, water and energy exchange in the 4 sites-areas using satellite data, the estimation of isoprene and monoterpene emissions using MEGAN model, the measurements performed and the first results. The isoprene and monoterpene emission rates estimated with MEGAN and emission factors measured at the foliar level for the dominant species ranged from about 0 to 0.2mgm-2h-1 in April. The warmer temperature in July resulted in higher model estimates from about 0 to ca. 1.6mgm-2h-1 for isoprene and ca. 4.5mgm-2h-1 for monoterpenes, depending on the site vegetation and footprint area considered. There were clear daily and seasonal patterns with higher emission rates and mixing ratios at midday and summer relative to early morning and early spring. There was a significant trend in CO2 fixation (from 1 to 10mgCm-2d-1), transpiration (from1-5kgCm-2d-1), and sensible and latent heat from the warmest-driest to the coolest-wettest site. The results showed the strong land-cover-specific influence on emissions of BVOCs, gas, energy and water exchange, and therefore demonstrate the potential for feed-back to atmospheric chemistry and climate. •We present a multidisciplinary biosphere-atmosphere field campaign.•We measured a gradient from semi-desertic shrublands to wet temperate forests.•A wide range of instruments and vertical platforms were used.•Land cover strongly influenced emissions of BVOCs and gas, energy and water exchange.•Vegetation has strong potential for feed-back to atmospheric chemistry and climate. © 2013 Elsevier Ltd., We are indebted to the Spanish government projects CONSOLIDER INGENIO MONTES (CSD2008-00040), and CGL2010-17172 and the Catalan government project SGR2009-458. NCAR is sponsored by the U.S. National Science Foundation. The research was also partially funded by the Italian Ministry for Research and University under the project CarboItaly (FISR funds). RS was partially supported by a postdoctoral grant from Fundación Ramón Areces.

38 páginas, 10 figuras, 1 tabla., The capacity for volatile isoprenoid production under standardized environmental conditions at a certain time (ES, the emission factor) is a key characteristic in constructing isoprenoid emission inventories. However, there is large variation in published ES estimates for any given species partly driven by dynamic modifications in ES due to acclimation and stress responses. Here we review additional sources of variation in ES estimates that are due to measurement and analytical techniques and calculation and averaging procedures, and demonstrate that estimations of ES critically depend on applied experimental protocols and on data processing and reporting. A great variety of experimental setups has been used in the past, contributing to study-to-study variations in ES estimates. We suggest that past experimental data should be distributed into broad quality classes depending on whether the data can or cannot be considered quantitative based on rigorous experimental standards. Apart from analytical issues, the accuracy of ES values is strongly driven by extrapolation and integration errors introduced during data processing. Additional sources of error, especially in meta-database construction, can further arise from inconsistent use of units and expression bases of ES. We propose a standardized experimental protocol for BVOC estimations and highlight basic meta-information that we strongly recommend to report with any ES measurement. We conclude that standardization of experimental and calculation protocols and critical examination of past reports is essential for development of accurate emission factor databases., We thank the European Science Foundation (VOCBAS and INTROP programs) for travel support. The authors’ studies on BVOCs have been funded by the Estonian Ministry of Science and Education (grant SF1090065s07), the Estonian Science Foundation (grant 7645), European Commission through European Regional Fund (the Center of Excellence in Environmental Adaptation), the US National Science Foundation and the US Environmental Protection Agency, the Spanish Ministry of Science (grants CGL2006-04025/BOS and Consolider-Ingenio Montes CSD2008-00040), the Catalan Department of Science (grant SGR 2009-458), and the Max Planck Society. U. N., A. A., and R. K. M. ¨ acknowledge support from the Human Frontier Science Program.

A fast two-dimensional gas chromatography (GC-MS) method that uses heart-cutting and thermal extraction (TE) and requires no chemical derivatization was developed for the determination of anhydro-sugars in fine aerosols. Evaluation of the TE-GC-GC-MS method shows high average relative accuracy (≥90%), reproducibility (≤10% relative standard deviation), detection limits of less than 3 ng/μL, and negligible carryover for levoglucosan, mannosan, and galactosan markers. TE-GC-GC-MS- and solvent extraction (SE)-GC-MS-measured levoglucosan concentrations correlate across several diverse types of biomass burning aerosols. Because the SE-GC-MS measurements were taken 8 years prior to the TE-GC-GC-MS ones, the stability of levoglucosan is established for quartz filter-collected biomass burning aerosol samples stored at ultra-low temperature (−50 °C). Levoglucosan concentrations (w/w) in aerosols collected following atmospheric dilution near open fires of varying intensity are similar to those in biomass burning aerosols produced in a laboratory enclosure. An average levoglucosan-mannosan-galactosan ratio of 15:2:1 is observed for these two aerosol sets. TE-GC-GC-MS analysis of atmospheric aerosols from the US and Africa produced levoglucosan concentrations (0.01–1.6 μg/m3) well within those reported for aerosols collected globally and examined using different analytical techniques (0.004–7.6 μg/m3). Further comparisons among techniques suggest that fast TE-GC-GC-MS is among the most sensitive, accurate, and precise methods for compound-specific quantification of anhydro-sugars. In addition, an approximately twofold increase in anhydro-sugar determination may be realized when combining TE with fast chromatography.

During two field campaigns (OP3 and ACES), which ran in Borneo in 2008, we measured large emissions of estragole (methyl chavicol; IUPAC systematic name 1-allyl-4-methoxybenzene; CAS number 140-67-0) in ambient air above oil palm canopies (0.81 mg m−2 h−1 and 3.2 ppbv for mean midday fluxes and mixing ratios respectively) and subsequently from flower enclosures. However, we did not detect this compound at a nearby rainforest. Estragole is a known attractant of the African oil palm weevil (Elaeidobius kamerunicus), which pollinates oil palms (Elaeis guineensis). There has been recent interest in the biogenic emissions of estragole but it is normally not included in atmospheric models of biogenic emissions and atmospheric chemistry despite its relatively high potential for secondary organic aerosol formation from photooxidation and high reactivity with OH radical. We report the first direct canopy-scale measurements of estragole fluxes from tropical oil palms by the virtual disjunct eddy covariance technique and compare them with previously reported data for estragole emissions from Ponderosa pine. Flowers, rather than leaves, appear to be the main source of estragole from oil palms; we derive a global estimate of estragole emissions from oil palm plantations of ~0.5 Tg y−1. The observed ecosystem mean fluxes (0.44 mg m−2 h−1) and mean ambient volume mixing ratios (3.0 ppbv) of estragole are the highest reported so far. The value for midday mixing ratios is not much different from the total average as, unlike other VOCs (e.g. isoprene), the main peak occurred in the evening rather than in the middle of the day. Despite this, we show that the estragole flux can be parameterised using a modified G06 algorithm for emission. However, the model underestimates the afternoon peak even though a similar approach works well for isoprene. Our measurements suggest that this biogenic compound may have an impact on regional atmospheric chemistry that previously has not been accounted for in models and could become more important in the future due to expansion of the areas of oil palm plantation.

There is growing evidence that organo-nitrogen compounds may constitute a significant fraction of the aerosol nitrogen (N) budget. However, very little is known about the abundance and origin of this aerosol fraction. In this study, the concentration of organic nitrogen (ON) and major inorganic ions in PM2.5 aerosol were measured at the Duke Forest Research Facility near Chapel Hill, NC, during January and June of 2007. A novel on-line instrument was used, which is based on the Steam Jet Aerosol Collector (SJAC) coupled to an on-line total carbon/total nitrogen analyzer and two on-line ion chromatographs. The concentration of ON was determined by tracking the difference in concentrations of total nitrogen and of inorganic nitrogen (determined as the sum of N-ammonium and N-nitrate). The time resolution of the instrument was 30 min with a detection limit for major aerosol components of ~0.1 μg m−3. Nitrogen in organic compounds contributed ~33% on average to the total nitrogen concentration in PM2.5, illustrating the importance of this aerosol component. Absolute concentrations of ON, however, were relatively low (

Reactive gases and aerosols are produced by terrestrial ecosystems, processed within plant canopies, and can then be emitted into the above-canopy atmosphere. Estimates of the above-canopy fluxes are needed for quantitative earth system studies and assessments of past, present and future air quality and climate. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) is described and used to quantify net terrestrial biosphere emission of isoprene into the atmosphere. MEGAN is designed for both global and regional emission modeling and has global coverage with ~1 km2 spatial resolution. Field and laboratory investigations of the processes controlling isoprene emission are described and data available for model development and evaluation are summarized. The factors controlling isoprene emissions include biological, physical and chemical driving variables. MEGAN driving variables are derived from models and satellite and ground observations. Tropical broadleaf trees contribute almost half of the estimated global annual isoprene emission due to their relatively high emission factors and because they are often exposed to conditions that are conducive for isoprene emission. The remaining flux is primarily from shrubs which have a widespread distribution. The annual global isoprene emission estimated with MEGAN ranges from about 500 to 750 Tg isoprene (440 to 660 Tg carbon) depending on the driving variables which include temperature, solar radiation, Leaf Area Index, and plant functional type. The global annual isoprene emission estimated using the standard driving variables is ~600 Tg isoprene. Differences in driving variables result in emission estimates that differ by more than a factor of three for specific times and locations. It is difficult to evaluate isoprene emission estimates using the concentration distributions simulated using chemistry and transport models, due to the substantial uncertainties in other model components, but at least some global models produce reasonable results when using isoprene emission distributions similar to MEGAN estimates. In addition, comparison with isoprene emissions estimated from satellite formaldehyde observations indicates reasonable agreement. The sensitivity of isoprene emissions to earth system changes (e.g., climate and land-use) demonstrates the potential for large future changes in emissions. Using temperature distributions simulated by global climate models for year 2100, MEGAN estimates that isoprene emissions increase by more than a factor of two. This is considerably greater than previous estimates and additional observations are needed to evaluate and improve the methods used to predict future isoprene emissions.

We present the physical and chemical characterization of particulate matter (PM 2.5 ) emissions from simulated agricultural fires (AFs) of surface residuals of two major grain crops, rice ( Oryza sativa ) and wheat ( Triticum aestivum L.). The O 2 levels and CO/CO 2 ratios of the open burn simulations are typical of the field fires of agricultural residues. In the AF plumes, we observe predominantly accumulation mode (100–1000 nm) aerosols. The mean PM 2.5 mass emission factors from replicate burns of the wheat and rice residuals are 4.7±0.04 and 13.0±0.3 g kg −1 of dry biomass, respectively. The combustion-derived PM emissions from wheat are enriched in K (31% weight/weight, w/w) and Cl (36% w/w), whereas the PM emissions from rice are largely carbonaceous (84% w/w). Molecular level gas chromatography/mass spectrometry analysis of PM 2.5 solvent extracts identifies organic matter that accounts for as much as 18% of the PM mass emissions. A scarcity of detailed PM-phase chemical emissions data from AFs required that comparisons among other biomass combustion groups (wildfire, woodstove, and fireplace) be made. Statistical tests for equal variance among these groups indicate that the degree to which molecular emissions vary is compound dependent. Analysis of variance testing shows significant differences in the mean values of certain n -alkane, polycyclic aromatic hydrocarbon (PAH), oxy -PAH, and sugar marker compounds common to the biomass combustion types. Individual pairwise comparisons of means at the combustion group level confirm this result but suggest that apportioning airborne PM to these sources may require a more comprehensive use of the chemical emissions fingerprints. Hierarchical clustering of source test observations using molecular markers indicates agricultural fuels as distinct from other types of biomass combustion or biomass species. Rough approximations of the total potential PM 2.5 emissions outputs from the combustion of the wheat and rice surface residues are given. This agricultural activity could significantly contribute to emissions inventories at regional, national, and global geographic levels.

Microbial biomass, nitrifiers and denitrifiers in surface soil (0–10 cm) were quantified in a riparian zone restoration project at Coweeta, North Carolina, USA. Four treatments are included in this study: (1) a degraded (+N) riparian zone with continued compaction, vegetation removal, and nutrient addition (mow, roll, and nutrient addition); (2) a degraded ( −N) riparian zone with continued compaction and vegetation removal, but without nutrient addition (mow and roll only); (3) a restored riparian area (no grazing, cessation of manure and N fertilizer application and re-vegetation with natural regrowth for 2 years); and (4) reference riparian zone (no riparian zone degradation has occurred within the last 10 years). Mean microbial biomass C increased from winter (316 mg kg −1 ) to summer (593 mg kg −1 ), and decreased from summer to fall (265 mg kg −1 ). There were no significant changes in microbial biomass C with the cessation of manure and chemical fertilizer application in the degraded − N plot and with re-vegetation in the restored plot as compared to the degraded + N plot. Microbial biomass C level in the restored plot was comparable to that in the reference plot for most seasons. Restored plots had significant greater populations of denitrifiers than reference plots in the spring. Nitrifier numbers were lower in the degraded − N and restored plots than the degraded + N. Ammonium oxidizers in summer were more abundant (25,000 g −1 soil) in the degraded + N plot compared to (1000 g −1 soil) in the degraded − N and restored plots, and NO2 − oxidizers in the same period were more abundant (130,000 g −1 soil) in the degraded + N plot than that in the degraded − N and restored plots about (40,000 g −1 soil). The soil NO3 − concentrations were considerably lower in the degraded − N and restored plots than the degraded + N plot. Our results imply either cessation of manure and N fertilizer application or cessation of manure and N fertilizer and re-vegetation could contribute to restoration of degraded riparian zone through reducing numbers of nitrifiers. © 2003 Elsevier B.V. All rights reserved.

Fine particle matter with aerodynamic diameter2.5 microm (PM2.5) and gas-phase emissions from open burning of six fine (foliar) fuels common to fire-prone U.S. ecosystems are investigated. PM2.5 distribution is unimodal within the 10-450 nm range, indicative of an accumulation mode. Smoldering relative to flaming combustion shows smaller particle number density per unit time and median size. Over 100 individual organic compounds in the primarily carbonaceous (70% by mass) PM2.5 are chemically speciated by gas chromatography/mass spectrometry. Expressed as a percent of PM2.5 mass, emission ranges by organic compound class are as follows: n-alkane (0.1-2%), polycyclic aromatic hydrocarbon (PAH) (0.02-0.2%), n-alkanoic acid (1-3%), n-alkanedioic acid (0.06-0.3%), n-alkenoic acid (0.3-3%), resin acid (0.5-6%), triterpenoid (0.2-0.5%), methoxyphenol (0.5-3%), and phytosterol (0.2-0.6%). A molecular tracer of biomass combustion, the sugar levoglucosan is abundant and constitutes a remarkably narrow PM2.5 mass range (2.8-3.6%). Organic chemical signatures in PM2.5 from open combustion of fine fuels differ with those of residential wood combustion and other related sources, making them functional for source-receptor modeling of PM. Inorganic matter [PM2.5 - (organic compounds + elemental carbon)] on average is estimated to make up 8% of the PM2.5. Wavelength dispersive X-ray fluorescence spectroscopy and ion chromatography identify 3% of PM2.5 as elements and water-soluble ions, respectively. Compared with residential wood burning, the PM2.5 of fine fuel combustion is nitrate enriched but shows lower potassium levels. Gas-phase C2-C13 hydrocarbon and C2-C9 carbonyl emissions are speciated by respective EPA Methods T0-15 and T0-11A. They comprise mainly low molecular weight C2-C3 compounds and hazardous air pollutants (48 wt % of total quantified volatile organic carbon).

The Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen (BEACHON) project seeks to understand the feedbacks and inter-relationships between hydrology, biogenic emissions, carbon assimilation, aerosol properties, clouds and associated feedbacks within water-limited ecosystems. The Manitou Experimental Forest Observatory (MEFO) was established in 2008 by the National Center for Atmospheric Research to address many of the BEACHON research objectives, and it now provides a fixed field site with significant infrastructure. MEFO is a mountainous, semi-arid ponderosa pine-dominated forest site that is normally dominated by clean continental air but is periodically influenced by anthropogenic sources from Colorado Front Range cities. This article summarizes the past and ongoing research activities at the site, and highlights some of the significant findings that have resulted from these measurements. These activities include - soil property measurements; - hydrological studies; - measurements of high-frequency turbulence parameters; - eddy covariance flux measurements of water, energy, aerosols and carbon dioxide through the canopy; - determination of biogenic and anthropogenic volatile organic compound emissions and their influence on regional atmospheric chemistry; - aerosol number and mass distributions; - chemical speciation of aerosol particles; - characterization of ice and cloud condensation nuclei; - trace gas measurements; and - model simulations using coupled chemistry and meteorology. In addition to various long-term continuous measurements, three focused measurement campaigns with state-of-the-art instrumentation have taken place since the site was established, and two of these studies are the subjects of this special issue: BEACHON-ROCS (Rocky Mountain Organic Carbon Study, 2010) and BEACHON-RoMBAS (Rocky Mountain Biogenic Aerosol Study, 2011).

The Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen (BEACHON) project seeks to understand the feedbacks and inter-relationships between hydrology, biogenic emissions, carbon assimilation, aerosol properties, clouds and associated feedbacks within water-limited ecosystems. The Manitou Experimental Forest Observatory (MEFO) was established in 2008 by the National Center for Atmospheric Research to address many of the BEACHON research objectives, and it now provides a fixed field site with significant infrastructure. MEFO is a mountainous, semi-arid ponderosa pine-dominated forest site that is normally dominated by clean continental air, but is periodically influenced by anthropogenic sources from Colorado Front Range cities. This article summarizes the past and ongoing research activities at the site, and highlights some of the significant findings that have resulted from these measurements. These activities include: – soil property measurements, – hydrological studies, – measurements of high-frequency turbulence parameters, – eddy covariance flux measurements of water, energy, aerosols and carbon dioxide through the canopy, – biogenic and anthropogenic volatile organic compound emissions and their influence on regional atmospheric chemistry, – aerosol number and mass distributions, – chemical speciation of aerosol particles, – characterization of ice and cloud condensation nuclei, – trace gas measurements, and – model simulations using coupled chemistry and meteorology. In addition to various long-term continuous measurement, three focused measurement campaigns with state-of-the-art instrumentation have taken place since the site was established, and two of these are the subjects of this special issue: BEACHON-ROCS (Rocky Mountain Organic Carbon Study, 2010) and BEACHON-RoMBAS (Rocky Mountain Biogenic Aerosol Study, 2011).

Isoprene emissions from oak trees in the eastern USA play an important role in tropospheric ozone pollution. Oak trees (Quercus) emit an order of magnitude more isoprene than most other emitting tree species, and are by far the largest source of biogenic isoprene in the eastern US. We used Landsat TM data to measure oak tree abundance near Oak Ridge. Tennessee, to estimate fluxes of isoprene. The Landsat classification was performed using multi-date data: supervised classification techniques, and an iterative approach. Training sites were selected based on transect data, and ten vegetation classes were mapped. A supervised classification algorithm called the Spectral Angle Mapper was used to classify the data. Empirical vegetation emission data were used to estimate the isoprene flux from each of the vegetation classes. The resultant isoprene flux maps were compared with concentrations measured in the field, and a good correspondence was observed. We also compare the Landsat classification with three other landcover schemes including the USGS’s Global Landcover Classification, which is based on AVHRR data. Results from these landcover classifications are used as input for models that predict tropospheric ozone production and are used to investigate ozone control strategies.

Nonmethane hydrocarbons are ubiquitous trace atmospheric constituents yet they control the oxidation capacity of the atmosphere. Both anthropogenic and biogenic processes contribute to the release of hydrocarbons to the atmosphere. In this manuscript, the state of the science concerning biosynthesis, transport, and chemical transformation of hydrocarbons emitted by the terrestrial biosphere is reviewed. In particular, the focus is on isoprene, monoterpenes, and oxygen-ated hydrocarbons. The generated science during the last 10 years is reviewed to explain and quantify hydrocarbon emissions from vegetation and to discern impacts of biogenic hydrocarbons on local and regional atmospheric chemistry. Furthermore, the physiological and environmental processes controlling biosynthesis and production of hydrocarbon compounds are reported on. Many advances have been made on measurement and modeling approaches developed to quantify hydrocarbon emissions from leaves and forest ecosystems. A synthesis of the atmospheric chemistry of biogenic hydrocarbons and their role in the formation of oxidants and aerosols is presented. The integration of biogenic hydrocarbon kinetics and atmospheric physics into mathematical modeling systems is examined to assess the contribution of biogenic hydrocarbons to the formation of oxidants and aerosols, thereby allowing us to study their impacts on the earth's climate system and to develop strategies to reduce oxidant precursors in affected regions.

During the summer of 1992, isoprene emissions were measured in a mixed deciduous forest near Oak Ridge, Tennessee. Measurements were aimed at the experimental scale-up of emissions from the leaf level to the forest canopy to the mixed layer. Results from the scale-up study are compared to different canopy models for determining the leaf microclimate as input to isoprene emission algorithms. These include (1) no canopy effects, (2) a simple vertical scaling canopy model with a leaf energy balance, and (3) a numerical canopy model which accounts for leaf-sun geometries, photosynthesis, respiration, transpiration, and gas transport in the canopy. Initial evaluation of the models was based upon a standard emission rate factor of 90 μgC g-1 hr-1 (0.42 nmol g-1 s-1) taken from leaf cuvette measurements and a biomass density factor of 203 g m-2 taken from biomass surveys and a flux footprint analysis. The results indicated that predicted fluxes were consistent among the models to within approximately ±20%, but that the models overestimated the mean flux by about a factor of 2 and overestimated the maximum observed flux by 30 to 50%. Adjusting the standard emission factor and biomass density each downward by 20% yielded predicted means approximately 20% greater than the observed means and predicted maxima approximately 25% less than the observed maxima. Accounting for changes in biomass density as a function of direction upwind of the tower improved the overall model performance.

Des catalyseurs Pd-Pt/Al 2 O 3 ont ete prepares par reactions de surface controlees. La reduction des ions PtCl 6 2- peut se faire en utilisant comme reducteur l'hydrogene preadsorbe sur un catalyseur monometallique parent Pd/Al 2 O 3 (recharge), ou le palladium metallique lui-meme (reaction redox directe). Deux precurseurs (Pd(NH 3 ) 4 Cl 2 and Pd(Acac) 2 ) ont ete utilises pour preparer le catalyseur parent 1% Pd/Al 2 O 3 . La charge en platine est de l'ordre de 0,13-0,14%. La caracterisation des catalyseurs a ete faite par chimisorption d'hydrogene, spectroscopie infrarouge d'adsorption de CO (comme molecule sonde) et E.X.A.F.S. Les deux methodes de preparation menent a differents depots du platine, quel que soit le catalyseur parent. En utilisant de l'hydrogene preadsorbe, le platine peut se deposer en decoration sur les sites de faible coordination (coins, aretes,...) des particules de palladium. Par reaction redox directe, le depot des atomes de platine a lieu preferentiellement sur les plans (111) des particules de palladium. Toutefois un phenomene de frittage peut etre observe, specialement pendant le traitement sous hydrogene en milieu aqueux. Ce frittage est exalte par la presence d'ions chlorures.

The capacity for volatile isoprenoid production under standardized environmental conditions (ES), the emission factor) is a key characteristic in constructing isoprenoid emission inventories. However, there is large variation in published ES estimates for any given species, and this variation leads to significant uncertainties in emission predictions. We review the sources of variation in ES that are due to measurement and analytical techniques and calculation and averaging procedures. This review demonstrates that estimations of ES critically depend on applied experimental protocols and on data processing and reporting. A great variety of experimental setups has been used in the past, contributing to study-to-study variations in ES estimates. We suggest that past experimental data should be distributed into broad quality classes depending on whether the data can or cannot be considered quantitative based on rigorous experimental standards. Apart from analytical issues, the accuracy of ES values is strongly driven by extrapolation and integration errors introduced during data processing. Additional sources of error, especially in meta-database construction, can further arise from inconsistent use of units and expression bases of ES. We propose a standardized experimental protocol for BVOC estimations and highlight basic meta-information that we strongly recommend to report with any ES measurement. We conclude that standardization of experimental and calculation protocols and critical examination of past reports is essential for development of accurate emission factor databases.

The properties of three-way automotive PtRh/Al 2 O 3 CeO 2 catalysts prepared either by coimpregnation of the two noble metals (CI catalysts) or by a newly devised technique of successive impregnations with an intermediate reducing treatment (SI catalysts) were investigated for the oxidation of a propane—propene mixture under lean conditions and for the CO + NO reaction. After high-temperature aging, bimetallic CI catalysts are far less active than SI catalysts for propane oxidation. On the other hand, they show comparable activities for propene oxidation and reaction CO + NO. The characterization of bimetallic catalysts by TPR and FT-IR experiments suggests that the coimpregnation leads to an intimate interaction between platinum and rhodium while rhodium added by successive impregnations with a reduction step after platinum impregnation would be selectively deposited onto cerium oxide surface in the vicinity of platinum particles, avoiding the formation of Pt/Rh alloy.

RhCu bimetallic catalysts were prepared by catalytic reduction under hydrogen of Cu2+ on Rh/Al2O3 parent catalysts, and were characterized using infrared spectroscopy of adsorbed carbon monoxide and hydrogenolysis of methylcyclopentane. Significant changes in the IR spectra as well as in the reactivity were observed upon addition of copper to Rh only if Rh/Al2O3 was well dispersed. This suggests that copper is selectively deposited on Rh surface atoms with a low coordination number. Comparison of methylcyclopentane conversion and IR spectral results for RhS and RhCu showed that charge transfer could take place from Rh atoms at the phase boundary to sulfur and from copper to partially oxidized rhodium.

Multimetallic catalysts exhibit some interesting properties which cannot be expected from the individual components alone. Some spectacular changes in activity and selectivity have been reported, resulting from the addition of a second metal to metallic catalysts [l-6]. The consequent changes were attributed in terms of “ligand (or electronic )” and “ensemble (or geometric)” effects. The concept of the “ensemble effect” is based on the assumption that adsorption or catalytic activation steps require more than one surface atom. On the other hand, the “ligand effect” concept is based on the assumption that the electronic properties, and so the catalytic properties, of a metallic surface atom are influenced by its surroundings and by the nature of the neighbouring metallic atoms. The frequency of the infrared band of adsorbed carbon monoxide can be altered by alloying and such shifts are considered to be evident of the occurrence of a ligand effect [ 71. Several surface species of carbon monoxide absorption on supported rhodium were detected by IR spectroscopy. The dominant ones are linearly bonded carbon monoxide (adsorbing at 2040-2076 cm-‘), the bridged for (adsorbing at 1845-1920 cm-l) and the gem dicarbonyl, Rh(CO),, (yielding bands at 2090-2105 and 2022-2032 cm-’ corresponding to the symmetrical and antisymmetrical vibrations [ 8-91. If the formation of linearly and bridged-bonded carbon monoxide species is ascribed to adsorption on a metallic rhodium surface, it is generally accepted that the gem dicarbonyl species is formed on isolated Rh’ sites. The most probable route for the formation of such positively charged rhodium is the oxidation of rhodium atoms by the OH groups of the support during carbonylation [lo]. The purpose of this note is to define by IR studies, the role of copper deposition on Rh/Al& catalysts, by studying the modifications induced by carbon monoxide adsorption on Rh/A1203 and Rh-Cu/AlzO, catalysts. A series of Rh/A1203 was prepared by exchanging the support (RhBne-Poulenc GFS C alumina) with an aqueous solution of rhodium chloride. The metal

Localized estimates of biogenic volatile organic compound (BVOC) emissions are important inputs for photochemical oxidant simulation models. Since forest tree species are the primary emitters of BVOCs, it is important to develop reliable estimates of their areal coverage and BVOC emission rates. A new system is used to estimate these emissions in the Atlanta area for specific tree genera at hourly and county levels. The U.S. Department of Agriculture, Forest Service Forest Inventory and Analysis data and an associated urban vegetation survey are used to estimate canopy occupancy by genus in the Atlanta area. A simple canopy model is used to adjust photosynthetically active solar radiation at five vertical levels in the canopy. Lraf temperature and photosynthetically active radiation derived from ambient conditions above the forest canopy are then used to drive empirical equations to estimate genus level emission rates of BVOCs vertically through forest canopies. These genera-level estimates are then aggregated to county and regional levels for input into air quality models and for comparison with (1) the regulatory model currently used and (2) previous estimates for the Atlanta area by local researchers. Estimated hourly emissions from the three approaches during a documented ozone event day are compared. The proposed model yields peak diurnal isoprene emission rates that are over a factor of three times higher than previous estimates. This results in total BVOC emission rates that are roughly a factor of two times higher than previous estimates. These emissions are compared with observed emissions from forests of similar composition. Possible implications for oxidant events are discussed.

In this paper, we present two years of seasonal nitric oxide (NO), ammonia (NH3), and nitrous oxide (N2O) trace gas fluxes measured in a recovering riparian zone with cattle excluded and adjacent riparian zone grazed by cattle. In the recovering riparian zone, average NO, NH3, and N2O fluxes were 5.8, 2.0, and 76.7 ng N m(-2) S(-1) (1.83, 0.63, and 24.19 kg N ha(-1) y(-1)), respectively. Fluxes in the grazed riparian zone were larger, especially for NO and NH3, measuring 9.1, 4.3, and 77.6 ng N m(-2) S(-1) (2.87, 1.35, and 24.50 kg N ha(-1) y(-1)) for NO, NH3, and N2O, respectively. On average, N2O accounted for greater than 85% of total trace gas flux in both the recovering and grazed riparian zones, though N2O fluxes were highly variable temporally. In the recovering riparian zone, variability in seasonal average fluxes was explained by variability in soil nitrogen (N) concentrations. Nitric oxide flux was positively correlated with soil ammonium (NH4+) concentration, while N2O flux was positively correlated with soil nitrate (NO3-) concentration. Ammonia flux was positively correlated with the ratio of NH4+ to NO3-. In the grazed riparian zone, average NH3 and N2O fluxes were not correlated with soil temperature, N concentrations, or moisture. This was likely due to high variability in soil microsite conditions related to cattle effects such as compaction and N input. Nitric oxide flux in the grazed riparian zone was positively correlated with soil temperature and NO3- concentration. Restoration appeared to significantly affect NO flux, which increased approximately 600% during the first year following restoration and decreased during the second year to levels encountered at the onset of restoration. By comparing the ratio of total trace gas flux to soil N concentration, we show that the restored riparian zone is likely more efficient than the grazed riparian zone at diverting upper-soil N from the receiving stream to the atmosphere. This is likely due to the recovery of microbiological communities following changes in soil physical characteristics.

Publisher Summary This chapter discusses biophysical feedbacks among plants that produce volatile organic compounds (VOCs) and the overlying atmosphere. The potential for feedbacks among global environmental change, phytogenic hydrocarbons, and associated atmospheric chemistry requires coordinated research efforts. In particular, new research is required to ascertain the way environmental changes occurring at the global scale might affect VOC emissions from ecosystems to the atmosphere. This research should take into account (1) warming from increased greenhouse gas concentrations and from other perturbations, (2) elevated carbon dioxide (CO 2 ) levels, (3) increased deposition of nitrogen, and (4) the conversion of land from unmanaged to managed ecosystems. An environmental change that is occurring locally and across the globe and that may be of great relevance to biogenic VOC production is the increased deposition of reactive nitrogen. The chapter, therefore, proposes a framework of vegetation controlled atmosphere dynamics consisting of three linked feedback loops, operating on different time scales. Feedback Loop I represents the vegetation-nocturnal temperature feedback. Feedback Loop II comprises VOC conversion to aerosols on which water vapor condensation occurs. For Loop III, it is proposed that with elevated nocturnal temperatures, neo-tropical plant species become more successful at higher latitudes with photosynthetic and VOC production capabilities over a longer portion of a year.

[1] Mixing ratios of isoprene, methyl vinyl ketone (MVK), and methacrolein (MACR) were determined continuously during an 8-day period in the summer of 1998 at a rural forested site located within the University of Michigan Biological Station (UMBS). The measurements were obtained as part of the Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET) study. Fluxes of isoprene were concurrently measured at a nearby tower (AmeriFlux, located 132 m north-northeast of the PROPHET tower). Following the study, 1-km-resolution emission estimates were derived for isoprene within a 60-km radius of the tower using forest density estimates (Biogenic Emissions Inventory System (BEIS3) model). Measured isoprene fluxes at the site compared well with modeled isoprene fluxes when using BEIS3 and a detailed leaf litter-fall data set by tree species from the UMBS site. Mean midday (1000–1400 LT) mixing ratios for isoprene, MACR, and MVK were 1.90 ± 0.43, 0.07 ± 0.01, and 0.14 ± 0.04 ppbv, respectively. Median midday mixing ratios of these compounds were 1.96 ± 0.26, 0.06 ± 0.02, and 0.10 ± 0.02 ppbv, respectively. Ratios of the isoprene oxidation products to isoprene are understood in the context of previous laboratory and field measurement studies of these compounds and a simple consecutive reaction scheme model. Results of the model indicate that the air masses studied represented relatively fresh emissions with a photochemical age of measured isoprene between 3.6 and 18 min, which is significantly less than the photochemical lifetime of isoprene (τ = 45 min at [OH] = 3.35 × 106 molecules cm−3). Thus a large portion of the isoprene that reaches the manifold has not had time to react completely with OH, yielding lower than expected ratios based on model calculations that do not explicitly take this into account. A rapid decrease in isoprene mixing ratios was observed soon after sunset, followed by a slower decay throughout the rest of the night. Emission maps were generated indicating that isoprene fluxes are highest in the immediate vicinity of the tower compared to the surrounding area of the site. Thus vertical diffusion and advection from the surrounding region are postulated to cause the observed initial rapid decrease in isoprene at the site. The second isoprene decay may be due to chemistry and/or dynamics, but the effects cannot be separated with the available data.

Biogenic emissions of volatile organic compounds {VOC) from forests play an important role in regulating the atmospheric trace gas composition including global tropospheric ozone concentrations. However, more information is needed on VOC emission rates from different forest regions of the world to understand regional and global impacts and to implement possible mitigation strategies. The mixed deciduous and coniferous forests of northern Wisconsin, USA were predicted to have significant VOC emission rates because they are comprised of many genera (i.e. Picea, Populus, Quercus, Salix) known to be high VOC emitters. In July 1993, a study was conducted on the Chequamegon National Forest near Rhinelander, WI to identify and quantify VOC emitted from major trees, shrubs, and understory herbs in the mixed northern forests of this region. Emission rates were measured at various scales -at the leaf level with cuvettes, the branch level with branch enclosures, the canopy level with a tower based system, and the landscape level with a tethered balloon air sampling system. Area-average emission rates were estimated by scaling, using biomass densities and species composition along transects representative of the study site. Isoprene (C5H8) was the primary VOC emitted, although significant quantities of monoterpenes (C10H16) were also emitted. The highest emission rates of isoprene (at 30C and photosynthetically active radiation of 1000 umolm-2s-1) were from northern red oak (Quercus rubra. > 110 ug(C)g-1h-1): aspen (Populus tremuloides. > 77): willow (Salix spp.. > 54): and black spruce (Picea mariamz. > 101. Emission rates of hybrid poplar clones ranged from 40 to 90 ug(C)g-1h-1 at 25C: those of Picea provenances were generally

Biogenic volatile organic compounds (BVOCs) were measured on tethered balloon platforms in 11 deployments between 1985 and 1996. A series of balloon sampling packages have been used to describe boundary layer dynamics, BVOC distribution, chemical transformations of BVOCs, and to estimate BVOC emission rates from terrestrial vegetation. Measurements indicated a slow decrease of concentration for BVOCs with altitude in the mixed layer when sampling times were greater than average convective turnover time; surface layer concentrations were more variable because of proximity to various emission sources in the smaller surface layer footprint. Mixed layer concentrations of isoprene remained fairly constant in the middle of the day, in contrast to canopy-level isoprene concentrations, which continued to increase until early evening. Daytime emissions, which increase with temperature and light, appear to be balanced by changes in entrainment and oxidation. Daytime measurements of methacrolein and methyl vinyl ketone, reaction products of the atmospheric oxidation of isoprene, showed fairly constant ratio to each other with altitude throughout the mixed layer. BVOC emission flux estimates using balloon measurements and from the extrapolation of leaf level emissions to the landscape scale were in good agreement.

Continuous measurements of whole canopy isoprene emissions over an entire growing season are reported from Harvard Forest (42°32′N, 72°11′W). Emissions were calculated from the ratio of observed CO2 flux and gradient multiplied by the observed hydrocarbon gradients. In summer 1995, 24-hour average emissions of isoprene from June 1 through October 31 were 32.7×1010 molecules cm−2 s−l (mg C m−2 h−l = 2.8 × 1011 molecules cm−2 s−1), and the mean midday mixing ratio was 4.4 ppbv at 24 m. Isoprene emissions were zero at night, increased through the morning with increasing air temperature and light, reached a peak in the afternoon between the peaks in air temperature and light, and then declined with light. Isoprene emissions were observed over a shorter seasonal period than photosynthetic carbon uptake. Isoprene emission was not detected from young leaves and reached a peak rate (normalized for response to measured light and temperature conditions) 4 weeks after leaf out and 2 weeks after emissions began. The normalized emission rate remained constant for approximately 65 days, then decreased steadily through September and into October. Total isoprene emissions over the growing season (42 kg C ha−1 yr−1) were equal to 2% of the annual net uptake of carbon by the forest. Measured isoprene emissions were higher than the Biogenic Emission Inventory System-II model by at least 40% at midday and showed distinctly different diurnal and seasonal emission patterns. Seasonal adjustment factors (in addition to the light and temperature factors) should be incorporated into future empirical models of isoprene emissions. Comparison of measured isoprene emissions with estimates of anthropogenic volatile organic compound emissions suggests that isoprene is more important for ozone production in much of Massachusetts on hot summer days when the highest ozone events occur.

The role of biogenic hydrocarbons on ozone modeling has been a controversial issue since the 1970s. In recent years, changes in biogenic emission algorithms have resulted in large increases in estimated isoprene emissions. This paper describes a recent algorithm, the second generation of the Biogenic Emissions Inventory System (BEIS2). A sensitivity analysis is performed with the Regional Acid Deposition Model (RADM) to examine how increased isoprene emissions generated with BEIS2 can influence the modeling of elevated ozone concentrations and the response of ozone to changes to volatile organic compound (VOC) and nitrogen oxide (NOx) emissions across much of eastern North America. Increased isoprene emissions are found to produce a predicted shift in elevated ozone concentrations from VOC sensitivity to NOx sensitivity over many areas of eastern North America. Isoprene concentrations measured near Scotia, Pennsylvania, during the summer of 1988 are compared with RADM estimates of isoprene and provide support for the veracity of the higher isoprene emissions in BEIS2, which are about a factor of 5 higher than BEIS1 during warm, sunny conditions. Copyright 1998 by the American Geophysical Union.

Isoprene is usually the dominant natural volatile organic compound emission from forest ecosystems, especially those with a major broadleaf deciduous component. Here we report isoprene emission model performance versus leaf and canopy level isoprene emission measurements made at the Duke University Research Forest near Chapel Hill, North Carolina. Emission factors, light and temperature response, canopy environment models, foliar mass, leaf area, and canopy level isoprene emission were evaluated in the field and compared with model estimates. Model components performed reasonably well and generally yielded estimates within 20% of values measured at the site. However, measured emission factors were much higher in early summer following an unusually dry spring. These decreased later in the summer but remained higher than values currently used in emission models. There was also a pronounced decline in basal emission rates in lower portions of the canopy which could not be entirely explained by decreasing specific leaf weight. Foliar biomass estimates by genera using basal area ratios adjusted for crown form were in excellent agreement with values measured by litterfall. Overall, the stand level isoprene emissions determined by relaxed eddy accumulation techniques agreed reasonably well with those predicted by the model, although there is some evidence for underprediction at ambient temperatures approaching 30°C, and overprediction during October as the canopy foliage senesced. A "Big Leaf" model considers the canopy as a single multispecies layer and expresses isoprene emission as a function of leaf area rather than mass. This simple model performs nearly as well as the other biomass-based models. We speculate that seasonal water balance may impact isoprene emission. Possible improvements to the canopy environment model and other components are discussed.

Natural volatile organic compound (VOC) fluxes were measured in three U.S. woodlands in summer 1993. Fluxes from individual leaves and branches were estimated with enclosure techniques and used to initialize and evaluate VOC emission model estimates. Ambient measurements were used to estimate above canopy fluxes for entire stands and landscapes. The branch enclosure experiments revealed 78 VOCs. Hexenol derivatives were the most commonly observed oxygenated compounds. The branch measurements also revealed high rates of isoprene emission from three genera of plants (Albizia, Chusqua and Mahonia) and high rates of monoterpene emission from three genera (Atriplex, Chrysthamnus and Sorbus) for which VOC emission rates have not been reported. Measurements on an additional 34 species confirmed previous results. Leaf enclosure measurements of isoprene emission rates from Quercus were substantially higher than the rates used in existing emission models. Model predictions of diurnal variations in isoprene fluxes were generally within +/- 35% of observed flux variations. Measurements with a fast response analyzer demonstrated that 60 min is a reasonable time resolution for biogenic emission models. Average daytime stand scale (hundreds of m) flux measurements ranged from about 1.3 mg C m(-2) h(-1) for a shrub oak stand to 1.5-2.5 mg C m(-2) h(-1) for a mixed forest stand. Morning, evening and nighttime fluxes were less than 0.1 mg C m(-2) h(-1). Average daytime landscape scale (tens of km) flux measurements ranged from about 3 mg C m(-2) h(-1) for a shrub oak-aspen and rangeland landscape to about 7 mg C m(-2) h(-1) for a deciduous forest landscape. Fluxes predicted by recent versions (BEIS2, BEIS2.1) of a biogenic emission model were within 10 to 50% of observed fluxes and about 300% higher than those predicted by a previous version of the model (BEIS).

Regional estimates of biogenic volatile organic compound (BVOC) emissions are important inputs for models of atmospheric chemistry and carbon budgets. Since forests are the primary emitters of BVOCs, it is important to develop reliable estimates of their areal coverage and BVOC emission rate. A new system is developed to estimate these emissions for specific tree genera at hourly and county level resolution. The U.S. Department of Agriculture, Forest Service Forest Inventory and Analysis Eastwide Database is used to describe the areal extent, species composition, and tree diameter distributions of United States forests. Horizontal canopy occupancy by genera is then estimated as a function of diameter at breast height. Growing season peak foliar masses are derived from the empirical literature for canopies of deciduous and coniferous genera. A simple canopy model is used to adjust photosynthetically active solar radiation at five vertical levels in the canopy. Leaf temperature and photosynthetically active radiation derived from ambient conditions above the forest canopy are then used to drive empirical equations to estimate genus level emission rates of BVOCs vertically through forest canopies. These genera level estimates are then aggregated to regional levels for comparison with the regulatory model currently used and for input intomore » air quality models. The proposed model yields isoprene emission rate estimates for specific countries that are 5 to 10 times higher (and total BVOC emission rates that are 3 to 5 times higher) than the Environmental Protection Agency BVOC emission rate model currently used. Emission estimates of isoprene and monoterpenes from the new system compare favorably with rates measured at various forested sites in the United States.« less

Etude de l'influence du support, de la temperature de calcination et du pH de la solution d'impregnation sur la reduction a temperature programmee et sur la dispersion du catalyseur Cu/Al 2 O 3

A study by dielectric polarization, microcalorimetry, and infrared spectrometry has allowed us to demonstrate the role played by the halogen in interactions between a series of chlorinated and brominated derivatives of methane (considered as types of halogenated anesthetics) and two tertiary amides taken as models for an element of the membranes of the nervous cells. The inert organic solvent used was cyclohexane. The interactions are of the hydrogen bonding and (or) halogen bonding types.

The catalytic behaviour of two series of rhodium/alumina catalysts in carbon monoxide—hydrogen reactions was investigated. Chemisorption, titration and IR spectroscopy of chemisorbed carbon monoxide were used to characterize the catalysts. The first series which consisted of well-reduced and variously dispersed samples (dispersion 7%

Cette etude complete les resultats d’une etude anterieure, consacree a l’interpretation de l’influence des solvants chlores sur la stabilite des complexes par liaison hydrogene, interpretation quantitative basee sur la mise en evidence par polarisation dielectrique, d’interactions base-solvant chlore.On examine ici l'importance des corrections que pourrait apporter la prise en consideration des valeurs des coefficients d’activite, determinees a cet effet dans le cadre de cette etude. On recherche egalement, a l’aide de methodes spectrometriques (UV et IR) une confirmation de l’existence des interactions base-solvant chlore.