Forest plantations in the UK are often established on seasonally waterlogged peaty gley soils which often require site preparation (drainage and mounding) to lower the water table and prepare planting positions. Substantial changes in the physical environment of peaty gley soils can accompany site preparation including fluctuations in soil temperature and soil moisture. These and other changes can all affect soil properties and decomposition processes and well as the dynamics of CO2, CH4 and N2O. A field experiment was established at Harwood Forest (NE England) to investigate the effects of three site management practices (drainage, mounding and fertilisation) frequently used for afforestation and replanting on peaty gley soils in the UK on soil properties and various of C and N, environmental variables (soil temperature, water content and water table height) and emissions of CO2, CH4 and N2O. The relationship between GHG emissions and environmental variables was also examined. The experiment was laid out in a factorial split-plot design. Drainage decreased C and N concentration in the 10 cm soil layer. The soil bulk density in the 0 to 20 cm soil layer was increased by mounding. Drainage and fertilisation increased soil CO2 efflux, whereas mounding did not affect soil CO2 efflux. All three practices affected soil CH4 fluxes with drainage reducing the fluxes and mounding and fertilisation increasing the fluxes. Nitrous oxide emissions were significantly affected by mounding and fertilisation, with mounding decreasing emissions and fertilisation increasing emissions. Soil temperature was the main environmental factor controlling soil respiration in this site. Over the two years study drainage and fertilisation increased the total greenhouse budget by 13.1% and 97.9%, while mounding caused a reduction of−17.6%. Drainage plus mounding reduced the total greenhouse budget by 6.9%, while drainage plus mounding plus fertilisation increased the total greenhouse budget by 101.8%. There is a potential for up-scaling GHG emissions from newly drained peaty gley for inclusion in the UK Land Use Land-Use Change and Forestry (LULUCF) Greenhouse Gas Inventory. However up-scaling and evaluation of the net emissions requires high quality data from different sites newly drained for afforestation. More studies are needed if net fluxes from newly drained sites are to the included in the LULUCF Greenhouse Gas Inventory.

This thesis applies, evaluates and compares methods for estimating exposure to traffic-related pollution within a GIS environment. The methods were used in two contrasting case studies; Greater London and Sheffield, where they were selected on basis of data availability and resolution. The methods used in this research were CALINE3, DMRB, ADMS-Urban and ISC3 (air pollution dispersion models), kriging and co-kriging (spatial interpolation), SAVIAH (regression method) and traditional exposure indicators. Calculated estimates were validated by comparing them to monitored NO2 data. In the Sheffield case study the best methods were then used to analyse relationships between traffic-related pollution and respiratory health. Evaluation of the performance of the various methods found that none of the methods used in Greater London worked very well, although ISC3 and kriging tended to give more reliable results. In Sheffield DMR.B and SAVIAH gave the best estimates of monitored pollution levels. Traditional exposure indicators were only used in Sheffield of which ‘density of main roads within 150 metres’, ‘traffic flow within 150 metres’ and ‘HGV flow within 150 metres’ provided the most reliable estimates. In general, the quality of all exposure measures was highly dependent on the quality of input data. This is largely due to the fact that most variation of traffic-related pollution occurs close to main roads. In Greater London the quality of data was clearly inadequate. In Sheffield, where data was of a higher quality, results were better. No substantial or significant associations were found between the exposure measures and health outcome in the Sheffield case study. In Sheffield, this research also showed that passive sampling of NO2 provided a reliable measure of relative levels of air pollution across an urban area. It also showed that none of the models were able to detect raised NO2 concentrations due to accumulation of pollution from the city, as a result of wind direction. The results of this research show that, although the methods used here can help in the investigation of relationships between traffic-related pollution and health, there is a major need to improve methods for modelling exposure to air pollution. An important development could be to link different models together within a GIS environment, in order to improve the ability to use available information and exploit the different capabilities of the models. In order to detect the effects of traffic-related pollutants on chronic health, estimates are needed across large populations. Linkage of the methods applied here, would be particularly useful to model spatial and temporal variations in these types of studies

In the year 2000, croplands covered about 12% of the Earth’s ice-free land surface. Through cropland management, humankind momentarily appropriates about 25% of terrestrial ecosystem productivity. Not only are croplands a key element of human food supply, but also bear potential in increased carbon (C) uptake when best-practice land management approaches are adopted. A detailed assessment of the impact of land use on terrestrial ecosystems can be achieved by modelling, but the simulation of crop C cycling itself is a relatively new discipline. Observational data on crop net ecosystem exchange (NEE) are available only recently, and constitute an important tool for model development, diagnosis, and validation. Before crop functional types (CFT) had been introduced, however, large-scale biogeochemical models (BGCM) lacked crop-specific patterns of phenology, C allocation, and land management. As a consequence, the influence of cropland C cycling on biosphere-atmosphere C exchange seasonality and magnitude is currently poorly known. To date, no regional assessment of crop C cycling and yield formation exists that specifically accounts for spatially and temporally varying patterns of sowing dates within models. In this thesis, I present such an assessment for the first time. In the first step (chapter 2), I built a crop C mass balance model (SPAc) that models crop development and C allocation as a response to ambient meteorological conditions. I compared model outputs against C flux and stock observations of six different sites in Europe, and found a high degree of agreement between simulated and measured fluxes (R2 = 0.83). However, the model tended to overestimate leaf area index (LAI), and underestimate final yield. In a model comparison study (chapter 3), I found in cooperation with further researchers that SPAc best reproduces observed fluxes of C and water (owed to the model’s high temporal and process resolution), but is deficient due to a lack in simulating full crop rotations. I then conducted a detailed diagnosis of SPAc through the assimilation of C fluxes and biometry with the Ensemble Kalman Filter (EnKF, chapter 4), and identified potential model weaknesses in C allocation fractions and plant hydraulics. Further, an overestimation of plant respiration and seasonal leaf thickness variability were evident. Temporal parameter variability as a response to C flux data assimilation (DA) is indicative of ecosystem processes that are resolved in NEE data but are not captured by a model’s structure. Through DA, I gained important insights into model shortcomings in a quantitative way, and highlighted further needs for model improvement and future field studies. Finally, I developed a framework allowing for spatio-temporally resolved simulation of cropland C fluxes under observational constraints on land management and canopy greenness (chapter 5). MODIS (Moderate Resolution Imaging Spectroradiometer) data were assimilated both variationally (for sowing date estimation) and sequentially (for improved model state estimation, using the EnKF) into SPAc. In doing so, I was able to accurately quantify the multiannual (2000-2006) regional C flux and biometry seasonality of maize-soybean crop rotations surrounding the Bondville Ameriflux eddy covariance (EC) site, averaged over 104 pixel locations within the wider area. Results show that MODIS-derived sowing dates and the assimilation of LAI data allow for highly accurate simulations of growing season C cycling at locations for which groundtruth sowing dates are not available. Through quantification of the spatial variability in biometry, NEE, and net biome productivity (NBP), I found that regional patterns of land management are important drivers of agricultural C cycling and major sources of uncertainty if not appropriately accounted for. Observing C cycling at one single field with its individual sowing pattern is not sufficient to constrain large-scale agroecosystem behaviour. Here, I developed a framework that enables modellers to accurately simulate current (i.e. last 10 years) C cycling of major agricultural regions and their contribution to atmospheric CO2 variability. Follow-up studies can provide crucial insights into testing and validating large-scale applications of biogeochemical models.

This study investigated the use of optical remote sensing for estimating leaf and canopy scale light use efficiency (LUE) and carbon exchange. In addition, a new leaf level model capable of predicting dynamic changes in apparent reflectance due to chlorophyll fluorescence was developed. A leaf level study was conducted to assess the applicability of passive remote sensing as a tool to measure the reduction, and the subsequent recovery, of photosynthetic efficiency during the weeks following transplantation. Spectral data were collected on newly planted saplings for a period of 8 weeks, as well as gas exchange measurements of LUE and PAM fluorescence measurements. A set of spectral indices, including the Photochemical Reflectance Index (PRI), were calculated from the reflectance measurements. A marked depression in photosynthetic rate occurred in the weeks after outplanting followed by a gradual increase, with recovery occurring in the later stages of the experimental period. As with photosynthetic rate, there was a marked trend in PRI values over the study period but no trend was observed in chlorophyll based indices. The study demonstrated that hyperspectral remote sensing has the potential to be a useful tool in the detection and monitoring of the dynamic effects of transplant shock. Relationships between hyperspectral reflectance indices, airborne carbon exchange measurements and satellite observations of ground cover were then explored across a heterogeneous Arctic landscape. Measurements were collected during August 2008, using the University of Edinburgh’s research aircraft, from an Arctic forest tundra zone in northern Finland as part of the Arctic Biosphere Atmosphere Coupling at Multiple Scales (ABACUS) study. Surface fluxes of CO2 were calculated using the eddy covariance method from airborne data that were collected from the same platform as hyperspectral reflectance measurements. Airborne CO2 fluxes were compared to MODIS vegetation indices. In addition, LUE was estimated from airborne flux data and compared to airborne measurements of PRI. There were no significant relationships between MODIS vegetation indices and airborne flux observations. There were weak to moderate (R2 = 0.4 in both cases) correlations between PRI and LUE and between PRI and incident radiation. A new coupled physiological radiative transfer model that predicts changes in the apparent reflectance of a leaf, due to chlorophyll fluorescence, was developed. The model relates a physically observable quantity, chlorophyll fluorescence, to the sub leaf level processes that cause the emission. An understanding of the dynamics of the processes that control fluorescence emission on multiple timescales should aid in the interpretation of this complex signal. A Markov Chain Monte Carlo (MCMC) algorithm was used to optimise biochemical model parameters by fitting model simulations of transient chlorophyll fluorescence to measured reflectance spectra. The model was then validated against an independent data set. The model was developed as a precursor to a full canopy scheme. To scale to the canopy and to use the model on trans-seasonal time scales, the effects of temperature and photoinhibition on the model biochemistry needs to be taken into account, and a full canopy radiative transfer scheme, such as FluorMOD, must be developed.

There are few published direct measurements of the atmosphere-surface exchange of volatile organic compounds (VOCs), particularly for biogenic VOCs (BVOCs). Global modelling of atmospheric chemistry and transport of BVOCs has large uncertainties due to the very small number of measurements in tropical regions, which are responsible for half the global BVOC emissions. This thesis presents direct measurements of concentrations and ecosystem fluxes of BVOCs in different regions (Tropics, Mediterranean) using the approach of virtual disjunct eddy covariance (vDEC) combined with proton transfer reaction mass spectrometry (PTR-MS) – a real-time BVOC sensor. The field measurements also included methodological developments of the vDEC/PTR-MS approach, which will be of value to the wider flux measurement community. A novel approach to determining the lag time between the vertical wind measurement and the air concentration measurement has been developed that will greatly reduce the uncertainty in the derived flux measurements. In the laboratory, the selectivity of PTR-MS was investigated by designing an alternating drift-voltage mode (AD-PTR-MS) to discriminate between structural isomers detected at the same m/z channel, with monoterpenes used as model compounds. The results of the measurements, particularly from the rainforest and oil palm plantations in Borneo, are novel and therefore provide important experimental constraints on models of atmospheric emissions, chemistry and transport. For example, although parameters which work reasonably well can be derived for model algorithms for the emission of isoprene from the rainforest, their performance over oil palms was less good, because of circadian controls of emissions from oil palms. However, the larger problem is the measured basal emission rates (BERs) which are significantly smaller than those used by default in the global MEGAN model. Another novel finding was the high deposition velocities of MVK and MACR (isoprene first order oxidation products) which at the oil palm plantation commonly exceeded 1 cm s-1; this result has implications for atmospheric modelling. The successful field results relied on significant developments in software for data acquisition and processing, and operational optimisation of the PTR-MS instruments in the extreme humidity encountered during the fieldwork in Borneo.

Nitrogen (N) fluxes show a substantial variability at the landscape scale. Emissions are transferred by atmospheric, hydrological and anthropogenic dispersion between different landscape elements or ecosystems, e.g. farms, fields, forests or moorland. These landscape N fluxes can cause impacts to the environment, such as loss of biodiversity. The aim of this study is to illustrate how landscape N fluxes can be quantified by integrating atmospheric and fluvial fluxes in a Scottish landscape of 6 km x 6 km that contains intensively managed poultry farming, extensively managed beef and sheep farming, semi-natural moorland and woodland. Atmospheric ammonia (NH3) emissions of two deep pit free range layer poultry houses were estimated by high time-resolution measurements of NH3 concentrations and meteorological variables downwind of layer poultry houses and the application of an inverse Gaussian plume model. Atmospheric NH3 concentrations and deposition fluxes across the study landscape were studied at a resolution of 25 m x 25 m. The approach combined a detailed landscape inventory of all farm activities providing high resolution NH3 emission estimates for atmospheric dispersion modelling and an intensive measurement programme of spatial NH3 concentrations for verifying modelled NH3 concentrations. The spatially diverse emission pattern resulted in a high spatial variability of modelled mean annual NH3 concentrations (0.3 to 77.9 μg NH3 m-3) and dry deposition fluxes (0.1 to >100 kg NH3-N ha-1 yr-1) within the landscape. Annual downstream fluxes and variation in spatial concentration of dissolved inorganic nitrogen (NH4 + and NO3 -) and dissolved organic nitrogen (DON) were studied in the two main catchments within the study landscape (agricultural grassland vs. semi-natural moorland catchment). The grassland catchment was associated with an annual downstream total dissolved nitrogen (TDN) flux of 14.4 kg N ha-1 yr-1, which was 66% higher than the flux of 8.7 kg ha-1 yr-1 from the moorland catchment. This difference was largely due to the NO3 - flux being one order of magnitude higher in the grassland catchment. The contribution of DON to the TDN flux varied between the catchments with 49% in the grassland and 81% in the moorland catchment. Fluvial and atmospheric N fluxes were combined to derive N budgets of the two catchments. Agricultural activities accounted for the majority of N input to the catchments, with atmospheric deposition also playing a significant role, especially in the moorland catchment. Both catchments showed large stream export fluxes compared to their net import which suggests that their capacity of N storage is limited. This thesis quantifies major N fluxes in a study landscape and shows their large spatial variability. Agricultural activities dominate landscape N dynamics. The work demonstrates the importance of considering landscape N variability when attempting to reduce the environmental impact of agricultural activities.

The Maptaphut Industrial Estate is located on the Gulf of Thailand, Rayong Province. The area, which has been designated as a main centre for the petrochemical industry currently occupies 16 sq km and comprises petrochemical plants, chemical and fertilizer plants, refineries, construction plants, and steel industry; there are also residential and commercial areas (IEAT, 2004). There is a significant population around the site, with 24,000 inhabitants in the immediate vicinity according to Jadsri et a/ (2006). The estate has been held responsible for deaths and hospital admissions due to leaks and accidents dating back as far as 1997. Whilst the environmental and health and safety performance of the estate as a whole has significantly improved over recent years, there are still significant outpatient admission rates to Maptaphut hospital for respiratory illness, as recently reported by Jadsri et al. (2006), raising the question of whether local emissions are significantly contributing to ill health, or whether general background concentrations of pollutants from nearby road sources and from Rayong City are the main contributions. The main aim of this research, therefore, was to accurately model the dispersion of pollutants from the estate, and to attempt to quantify the health impacts of these emissions. The specific objectives of this study were to (a) to characterise meteorological conditions in the Maptaphut area; (b) to develop a multiple linear regression statistical model to characterise and predict atmospheric pollutant concentrations in Maptaphut; (c) to investigate the relationship between air pollution and ill health in Maptaphut using a multiple linear regression statistical model; (d) to evaluate the effectiveness of Gaussian and Computational Fluid Dynamics atmospheric dispersion modelling software packages in predicting ground level pollutant concentrations at points around the industrial estate and (e) to use the results of the dispersion modelling studies to assess the contribution of the industrial estate to the overall atmospheric pollutant load in the Maptaphut area, and from published health impact factors, to assess the overall health impact of the estate. The first objective was to characterise the environmental status, trend, and impacts of air pollution during the period 1998 to 2007. The estate is located in the coastal area; thus, the role of the sea-land breeze has a significant role in the dispersion of air pollutants harmfulness. Data collected for the Maptaphut Industrial Estates area, including regional, temporal and spatial considerations included: meteorological data from 100-metres tall meteorological mast; ambient air quality data from three ambient air quality monitoring stations; industrial emissions data; traffic volume on nearby major roads; and outpatient admissions data at the Maptaphut and Rayong hospitals. Comparisons with the ambient air quality in the Bangkok area were made, and the daily and yearly trends in concentrations of the main air pollutants were analysed. Multiple linear regression models correlating pollutant concentrations with respiratory outpatient admissions rates showed that 03, PMio and NO were statistically significant determinants. The overall correlation had a coefficient of Determination (R2) of 41.4% for one week average data, increasing to 51.2% when air temperature and %RH were included. Accumulation effect of pollutants up to four weeks period exposure does not appear to have an effect. A basic health impact analysis study using the ADMS modelled concentrations and the WHO AirQ tool, along with default risk factors, showed that emissions from the Maptaphut industrial estate account for almost all of the NO2 and SO2 related respiratory illness and between 10 and 27% of the PMio related admissions; this actually represents less than 2% of the total respiratory admissions for this area.

Le cobalt est un métal de transition essentiel pour la croissance du phytoplancton, et en particulier pour les cyanobactéries qui ont un besoin absolu pour cet élément. En étant l'atome central de la cobalamine (vitamine B12), le cobalt est aussi indirectement essentiel aux eucaryotes marins qui ne synthétisent pas cette vitamine. Cet élément peut se substituer au zinc et au cadmium au sein de la carbonique anhydrase, l’enzyme permettant la fixation du dioxyde de carbone dans la cellule phytoplanctonique. Il pourrait intervenir également dans l’activation de l’alcaline phosphatase. De par ses implications biologiques, le cobalt pourrait jouer un rôle important dans le cycle océanique du carbone. Cependant, les connaissances du cycle biogéochimique du cobalt en milieu marin sont encore largement limitées. Ce travail de thèse de doctorat s’inscrit dans le cadre du programme international GEOTRACES au sein duquel le cobalt y est désigné comme un élément clé de la biogéochimie marine. Au cours de ces travaux, l’un des plus larges jeux de données, rapporté à ce jour, incluant les différentes fractions du cobalt (soluble, dissous, particulaire, spéciation organique) a été produit. Les données recueillies proviennent d’échantillons collectés au sein de domaines océaniques contrastés. Une stratégie de prélèvement à haute résolution et à grande échelle a été mise en place dans diverses régions océaniques du monde lors de campagnes à la mer. Ainsi pour la première fois, une cartographie du cobalt dissous (DCo) et particulaire (PCo) a pu être définie pour l’ensemble de l’Atlantique Ouest, ainsi que des bassins Méditerranéens et de la Mer Noire. Ce jeu de données a pu être produit par l’utilisation de différentes techniques d’analyses (Flow-Injection-Analysis and Chemiluminescence detection ; Voltamétrie, SF-ICP-MS) aux limites de détections basses permettant la détermination de cet élément, présent dans l’eau de mer à des concentrations de l’ordre du pico-molaire (10-12 M). Le cobalt est en effet l’un des micro-nutritifs le moins abondant dans l’eau de mer. Les concentrations les plus faibles en DCo ont été observées dans les eaux oligotrophes de l’Atlantique Ouest (< 15 pM) alors que les plus élevées sont enregistrées dans la couche supérieure des eaux sulfidiques de la Mer Noire (> 5 nM). La distribution verticale du cobalt dissous variait selon les systèmes biogéochimiques. Ainsi, le profil vertical est de type nutritif comme les phosphates dans les eaux de surface de l’océan Atlantique. Les concentrations y augmentent avec la profondeur, jusqu’à un maximum relatif dans les eaux intermédiaires, puis décroissent dans l’océan profond. Ce comportement contraste avec le profil observé pour l’ensemble des bassins de la Mer Méditerranée. Dans cette mer, les fortes concentrations en DCo mesurées en surface (100-300 pM) diminuent en effet avec la profondeur. En Mer Noire, la distribution verticale varie selon les conditions d’oxygénation des eaux. Les concentrations y sont extrêmement élevées par comparaison aux autres systèmes marins. […] / No

La microflore joue un rôle majeur dans la mobilité des éléments métalliques et métalloïdes dans les sols. L’activité bactérienne globale d’oxydation de l’AsIII en AsV tend à diminuer la toxicité et la mobilité de l’arsenic (As) dans les sols, cependant l’effet de la matière organique (MO) sur cette activité n’a pas été déterminé jusqu’à présent. Il est important de répondre à cette question car sur des sites pollués, un apport de MO peut être préconisé dans le cadre d’opérations de phyto-stabilisation. Par ailleurs, dans un contexte de pollution diffuse, les pratiques agricoles d’amendement des sols pourraient avoir un impact sur le transfert d’As. L’objectif de ce projet de thèse était donc de quantifier l’influence de la MO sur la spéciation de l’As par la microflore de sols pollués, et les conséquences de ce processus sur la mobilité du métalloïde. L’influence de la MO sur la spéciation de l’As a été évaluée (1) au niveau physiologique et moléculaire, sur l’activité de deux souches pures et (2) au niveau global, par l’évaluation de l’activité d’oxydation de l’AsIII par les communautés microbiennes de sols pollués et des incubations de sols. L’effet de la nature même de la MO a été examiné à travers la comparaison de substrats simples et complexes. Les expériences réalisées avec les souches de Thiomonas delicata et Herminiimonas arsenicoxydans ont montré un effet négatif de la MO sur la vitesse spécifique d’oxydation de l’AsIII. L’extrait de levure (EdL) induit une diminution de l’expression du gène aioA codant pour la grande sous-unité de l’arsénite-oxydase permettant l’oxydation de l’arsenic, avec les deux souches pures. Au niveau plus global des communautés microbiennes de sols, l’activité AsIII-oxydantes a été évaluée sur 8 sols pollués par de l’As. Les mesures ont été effectuées dans des milieux de cultures contenant différentes concentrations de MO. Deux MO complexes ont été comparées : l’EdL et une mixture synthétique de molécules organiques (SMOM) dont la composition a été inspirée par les caractéristiques de la MO de sols réels (rapport C/N, contenu en groupes fonctionnels). Des corrélations ont été recherchées entre les caractéristiques des sols et la constante de vitesse d’oxydation de l’AsIII par la microflore, avec et sans ajout de MO. La vitesse d’oxydation de l’AsIII par la microflore des sols semble limitée par la MO disponible, et cette limitation est levée par un apport de 0,08 g.L-1 de C apporté sous forme d’EdL ou de SMOM. Lorsque l’apport de MO s’élève à 0,4 g.L-1 de C, des résultats divergents sont observés : l’EdL est moins inhibiteur que la SMOM. Enfin, une expérience a été réalisée dans le but d’évaluer l’influence combinée de l’activité microbienne et de l’apport de SMOM sur la mobilisation de l’As présent dans quatre sols pollués, incubés au laboratoire en suspension. Une mobilisation dans la phase aqueuse de l’As présent dans les sols pollués est observée en présence de SMOM et de microorganismes actifs. Ce travail de thèse apporte un éclairage sur le rôle important joué par le métabolisme de la MO au sein du cycle biogéochimique de l’As, phénomène devant être pris en compte lors des études visant à optimiser la remédiation des sites pollués / The soil microflora plays a major role in the mobilization of metals and metalloids in soils. The global bacterial oxidation of AsIII to AsV tends to decrease the toxicity and mobility of arsenic in soils. The effect of organic matter (OM) on bacterial AsIII oxidation in presence of oxygen and its potential impact on the behavior of arsenic in non-saturated soils has not been determined up to date. However, supply of OM on polluted sites can be proposed in the context of a phytostabilization operation. Furthermore, agricultural soils affected by diffuse As pollution may be fertilized by organic amendments that could impact arsenic transfer. The objective of the present PhD thesis was to quantify the influence of OM on the speciation of As by the polluted soil microflora and the consequences of this process on arsenic mobility. The influence of OM on the speciation of As was evaluated (1) at the physiological and molecular levels on two pure strains and (2) at global level by AsIII oxidation measurements by microbial communities from polluted soils and on soils incubations. The effect of the nature of OM was considered through the comparison of simple and complex substrates. The experiments with Thiomonas delicata and Herminiimonas arsenicoxydans showed a negative effect of OM on the specific AsIII oxidation rate. Yeast extract (YE) induced a decrease of aioA gene (encoding for the big subunit of arsenite oxidase responsible for AsIII oxidation) expression with both pure strains. At the level of soils microbial communities, AsIII oxidizing activity were measured on 8 As-polluted soils. Measurements were realized in culture media containing different concentrations of OM. Two complex OMs were compared: YE and a synthetic mixture of organic matters (SMOM) whose composition was inspired from soils OM characteristics (C/N ratio and proportion of functional groups). Correlations were searched between soils characteristics and AsIII bio-oxidation rate constants with and without added OM. Results indicate that AsIII oxidation rate by the soil microflora was limited by available OM and this limitation was removed by the addition of 0.08 g L-1 of organic C as YE or SMOM. When the addition of OM reached 0.4 g L-1 of C, divergent results were observed: YE was less inhibiting than SMOM. Finally, an experiment was carried out to evaluate the combined influence of microbial activity and SMOM addition on As mobilization from polluted soils incubated as slurries at laboratory scale. A mobilization of As present in the polluted soils was observed in presence of both SMOM and active microorganisms. This PhD thesis enlightens the important role played by OM metabolism within the biogeochemical cycle of As, which should be given consideration in the context of polluted site remediation

The complexity of the processes whereby organic species are degraded in the atmosphere prevents many of the individual species (intermediates or products) from being unambiguously identified. Laboratory work necessarily focuses therefore on studies of idealised proxies with the aim of increasing general understanding of the physical and chemical processes which occur on particles and the types of species which they produce. Studies of the ubiquitous proxy oleic acid have resulted in the development of complex reaction schemes describing the various products and intermediates. These schemes include a diverse range of reactions and rates, thus highlighting the complications associated even with a relatively simple system. This thesis describes novel experimental studies designed to increase understanding of heterogeneous ozonolysis reactions of organic species in the aerosol phase using infrared spectroscopy as the principal analytical method. Reactions have been studied in solution (supported by off-line mass spectrometry), in thin films and in aerosols. The sensitivity of the infrared technique has also enabled the kinetics of reactions in thin films and aerosols to be followed. These methods were applied to both single- and mixed-component systems. Product studies successfully identified a number of primary and secondary species in the ozonised systems, with the secondary products formed from association reactions of the Criegee Intermediates with other species present (including self-reaction). In the mixed organic system these products were found to have originated from both a single reactant and from cross reactions between moieties from two different reactants. At low relative humidity, the ozonolysis reaction rates were monitored through the loss of the reactant species by infrared spectroscopy in the thin film and aerosol phase to give reactive uptake coefficients (gamma). At high relative humidity, the formation of products was followed. For the single-component thin films, the values obtained were gamma = 7.8 x 10-5 for stilbene and gamma = 2.0 x 10-7 for anthracene. In thin mixed films of oleic acid and stilbene, segregation occurred which prevented the effect of mixing upon the rate to be measured. A reactive uptake of gamma = 6.8 x 10-5 was obtained, identical to that of pure oleic acid. In the particle phase, the functional form of the reaction kinetics was found to be dependent on the type of particle. Pure stilbene and mixed oleic/stilbene aerosols were highly reactive and it proved necessary to treat reactive uptake coefficients under both diffusion-limited and surface-only reaction scenarios. For stilbene, the values obtained were gamma = 1.5 x 10-3 and gamma = 5.3 x 10-3 respectively. Spectral limitations in the mixed system meant that only the reaction of stilbene could be followed, giving gamma = 4.4 x 10-3 and gamma = 10.0 x 10-3 respectively. The enhanced rate in the mixture was attributed to secondary reactions. Anthracene and oleic acid coated particles were treated using a Langmuir-Hinshelwood mechanism from which the parameters KO3 (ozone partitioning coefficient) and kImax (maximum pseudo-first-order rate coefficient) could be extracted. For anthracene ozonolysis KO3 = 1.4 x 10-16 cm3 molecule-1 and kImax = 3.5x10-2 s-1. For oleic acid coated onto ammonium sulfate aerosols, values obtained were KO3 = 2.35 x 10-15 cm3 molecule-1 and kImax = 0.56 s-1 at low RH% and KO3 = 1.71 x 10-16 cm3 molecule-1 and kImax =0.33 s-1 at high RH%. The reduction in reactivity with increased RH% is principally attributed to the effect of surface polarity on ozone absorption.