Aerosol particles affect the Earth’s climate, although their impact is associated with large uncertainties. Primary marine aerosol represents a significant fraction of the global aerosol budget considering the Earth’s 70-percentage coverage by oceans. They are produced when bubbles burst at the ocean surface and can consist of sea salt, organic matter and bacteria. An experimental approach was here used to investigate the primary marine aerosol production from the bubble-bursting mechanism using water from four different geographical locations. The main findings include: Similar and stable aerosol number size distributions at all locations, centered close to 0.2 μm. Largely varying aerosol organic fractions, both with size and location. Clear tendency for increased water temperature to negatively influence the aerosol production. No covariance between surface water chlorophyll α and aerosol production on a 10-minute time scale, although decreased aerosol production was observed at times of elevated phytoplankton activity on longer time scales. Mainly external mixtures of sea salt and organics was observed. A high tendency for colony-forming marine bacteria to use bubble-bursting to reach the atmosphere. A clear diurnal cycle in aerosol production was found for both laboratory produced aerosol and in-situ aerosol fluxes, probably biologically driven. The first near coastal sea spray fluxes with limited fetch and low salinity. While the primary marine aerosol spectral shape is stable, emission concentration varies with environmental parameters. Above that, the organic fraction of the aerosol varies largely between locations. This shows that observations of primary marine aerosol emissions not necessarily can be applied to large time- or spatial scales. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: In press. Paper 3: Manuscript. Paper 4: Manuscript.

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Les Composés Organiques Volatils (COV) jouent un rôle important dans la chimie de l'atmosphère et participent à la formation de polluants secondaires comme l'ozone et les aérosols organiques. Les émissions biogéniques de COV dominent d'un facteur dix les émissions anthropiques à l'échelle globale mais leur caractérisation à l'échelle régionale est incertaine. Les progrès en modélisation de la chimie atmosphérique passent par l'amélioration des inventaires d'émissions, ce qui nécessite des mesures de flux in situ. Ces travaux portent sur l'étude des émissions de COV biogéniques par les végétations méditerranéennes dans le cadre du programme ChArMEx (Chemistry and Aerosol Mediterranean Experiment) qui vise à concentrer les efforts scientifiques sur l'étude de la chimie et des aérosols de l'atmosphère du bassin méditerranéen. La méthode Eddy Covariance (EC) permet de quantifier directement les échanges d'espèces chimiques entre la surface et l'atmosphère. Cette méthode constitue une référence pour les mesures de flux mais n'est applicable qu'à un nombre limité d'espèces car elle requiert la mesure rapide (~ 0,1 s) et simultanée de la concentration du composé étudié ainsi que de la vitesse du vent vertical. Afin d'élargir le champ de mise en œuvre de cette technique d'autres solutions dérivées de l'EC ont été proposées, dont la méthode Disjunct Eddy Covariance (DEC) qui a pour particularité de réduire la contrainte sur la mesure rapide de l'espèce chimique tout en gardant une précision acceptable sur le calcul du flux. Dans le cadre de ces travaux de thèse un système de prélèvement a été développé pour mettre en œuvre la mesure de flux de COV par la méthode DEC. Ce dispositif appelé MEDEE (Mesures par Échantillonnage Disjoint des Échanges d'Espèces en trace) repose sur une technologie nouvelle qui permet une capture rapide d'un échantillon d'air et assure son transfert à pression constante vers un analyseur connecté en ligne. Il est composé de deux "seringues mécaniques" actionnées par des vérins électriques dont le fonctionnement est alterné pour alimenter en continu l'analyseur. Trois électrovannes disposées à l'entrée de chaque réservoir dirigent le flux d'air en fonction du cycle de fonctionnement. L'ensemble du système est cadencé par un microcontrôleur avec une précision à la milliseconde. Le système de prélèvement a été réalisé en matériaux inertes chimiquement pour éviter la dégradation de l'échantillon et être compatible avec les espèces en trace réactives. MEDEE a été testé et validé pour les mesures de flux au sol et en avion lors de deux campagnes de terrain. Le système MEDEE a ainsi permis, lors de deux campagnes de mesures pendant les étés 2010 et 2011 au-dessus d'une forêt de chênes pubescents, de mesurer les flux d'isoprène grâce à un couplage avec un analyseur adapté (Fast Isoprene Sensor). Un réseau de neurones artificiels (RNA) a ensuite été utilisé pour déterminer une paramétrisation des flux d'isoprène en fonction des paramètres environnementaux à partir des observations des campagnes de mesures. La modélisation des émissions d'isoprène a été validée pour les conditions environnementales rencontrées. Cette paramétrisation servira dans un modèle de chimie atmosphérique à l'étude de l'impact des émissions de COV biogéniques sur la qualité de l'air.

Net ecosystem carbon dioxide exchange (NEE) was measured using the eddy covariance (EC) technique at a wetland tundra-sedge fen near Churchill, Manitoba, Canada during two consecutive growing seasons (2007 and 2008). Mean daily NEE at the fen (DOY 157-254) was -3.5 (± 0.26 S.E.) g CO2 m-2 d-1 in 2007 and -4.6 (± 0.36) g CO2 m-2 d-1 in 2008. The fen was a net carbon dioxide (CO2) sink during both the 2007 and 2008 growing seasons of -343 (± 79) and -450 (± 87) g CO2 m-2, respectively. Mean air temperature during the summer (June 1-August 31) was about 1°C greater than the historical average (1971-2000) in 2007 and about 2°C greater in 2008. Growing season precipitation was 107.5 mm below normal in 2007 and 359.5 mm above normal in 2008. These data suggest that if future climate change brings warmer temperatures and near-to-above average precipitation maintaining the water table near the surface, similar subarctic ecosystems will experience increased gross ecosystem productivity enhancing CO2 sequestration during the growing season.

The eddy-covariance method was used to measure net ecosystem productivity over three adjacent fields from 2009 to 2011: two annual cropping systems (oat-canola-oat and hay-oat-fallow) recently converted from perennial cropping, and a perennial hay/pasture. We compared the management practises, determined the net carbon budget, and examined the effects of inter-annual variability. Carbon accumulation began earlier in the spring and continued later in the fall at the perennial site, compared with the annual crop sites, due to a longer growing season and continual plant cover. Cumulative cropping season net ecosystem productivity at the perennial site ranged from 40 to 240 g C m^(-2) because of variable weather. Including harvest removals and manure additions, the perennial site gained 120 g carbon m^(-2) and the annual sites lost 240 and 415 g carbon m^(-2), respectively, over the 30-month period. This indicates that the annual cropping systems would decrease soil carbon at this location.

Net ecosystem carbon dioxide exchange (NEE) was measured using the eddy covariance (EC) technique at a wetland tundra-sedge fen near Churchill, Manitoba, Canada during two consecutive growing seasons (2007 and 2008). Mean daily NEE at the fen (DOY 157-254) was -3.5 (± 0.26 S.E.) g CO2 m-2 d-1 in 2007 and -4.6 (± 0.36) g CO2 m-2 d-1 in 2008. The fen was a net carbon dioxide (CO2) sink during both the 2007 and 2008 growing seasons of -343 (± 79) and -450 (± 87) g CO2 m-2, respectively. Mean air temperature during the summer (June 1-August 31) was about 1°C greater than the historical average (1971-2000) in 2007 and about 2°C greater in 2008. Growing season precipitation was 107.5 mm below normal in 2007 and 359.5 mm above normal in 2008. These data suggest that if future climate change brings warmer temperatures and near-to-above average precipitation maintaining the water table near the surface, similar subarctic ecosystems will experience increased gross ecosystem productivity enhancing CO2 sequestration during the growing season.

The eddy-covariance method was used to measure net ecosystem productivity over three adjacent fields from 2009 to 2011: two annual cropping systems (oat-canola-oat and hay-oat-fallow) recently converted from perennial cropping, and a perennial hay/pasture. We compared the management practises, determined the net carbon budget, and examined the effects of inter-annual variability. Carbon accumulation began earlier in the spring and continued later in the fall at the perennial site, compared with the annual crop sites, due to a longer growing season and continual plant cover. Cumulative cropping season net ecosystem productivity at the perennial site ranged from 40 to 240 g C m^(-2) because of variable weather. Including harvest removals and manure additions, the perennial site gained 120 g carbon m^(-2) and the annual sites lost 240 and 415 g carbon m^(-2), respectively, over the 30-month period. This indicates that the annual cropping systems would decrease soil carbon at this location.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Farming systems can act as a source or sink of atmospheric carbon, depending on the type of culture and soil management system adopted. This thesis presents a comparative study between the data obtained from two micrometeorological stations installed on the corn crop, in order to assess the impact of two tillage systems for corn (conventional tillage-CT and no-till-NT) in net ecosystem exchange of carbon fluxes (NEE). The flux were evaluated by the method of eddy covariance (EC), during the 156 days of maize. The results show that the two systems of planting corn act as drain CO2 −C and that there is a difference in the absorption ofCO2−C between the two planting systems with a NT with higher net exchange of carbon in the ecosystem in relation to CT . The biggest difference between the systems occurs in the first half cycle of corn, and after 40 days the cultures behave as a source of CO2−C, with higher values of CT issue at this time in relation to NT, and from then culture behaves as CO2−C drain. We conducted a study on the relative role of low-frequency and turbulent processes in the nocturnal boundary layer through the analysis of two-point correlations of wind components. Noting that the low-frequency processes dominate the two-point correlations in weak wind conditions, that the vertical two-point correlations of the spanwise component are negative at the very low time scale limit and that the statistical properties of the turbulent field are preserved horizontally over distances for which the two-points correlation have already been largely reduced. / Os sistemas agrícolas podem atuar como dreno ou fonte de carbono atmosférico, dependendo do tipo da cultura e do sistema de manejo do solo adotado. Este trabalho apresenta um estudo comparativo entre os dados obtidos a partir de duas estações micrometeorológicas instaladas sobre a cultura de milho, com o objetivo de avaliar o impacto de dois sistemas de semeadura de milho (preparo convencional-PC e plantio direto-PD) na troca líquida do ecossistema dos fluxos de carbono (NEE). Os fluxos foram avaliados pelo método de covariância de vórtices turbulentos (MCV), durante o período de 156 dias da cultura do milho. Os resultados obtidos mostram que os dois sistemas de cultivo de milho atuam como dreno de C−CO2 e que a há uma diferença quanto a absorção de C−CO2 entre os dois sistemas de plantio, com o PD apresentando maior troca líquida de carbono no ecossistema em relação ao PC. A maior diferença entre os sistemas ocorre na primeira metade do ciclo da cultura do milho, sendo que nos primeiros 40 dias as culturas se comportam como fonte de C−CO2, com o PC apresentando valores maiores de emissão neste período em relação ao PD, e a partir de então a cultura se comporta como dreno de C−CO2. Realizou-se um estudo sobre o papel relativo das baixa frequências e dos processos turbulentos na camada limite noturna através da análise de correlações de dois pontos das componentes do vento. Verificando-se que os processos de baixa frequência dominam as correlações de dois ponto em condições de vento fraco, que as correlações verticais de dois pontos da componente lateral do vento são negativas no limite de escala de tempo muito baixa e que as propriedades estatísticas do campo turbulento são preservadas horizontalmente ao longo de distâncias para os quais as correlações de dois pontos já foram largamente reduzidos.

Submitted by Lucienne Costa (lucienneferreira@ufcg.edu.br) on 2018-08-28T16:36:07Z No. of bitstreams: 1 CELINA CÂNDIDA FERREIRA RODRIGUES – DISSERTAÇÃO (PPGMET) 2018.pdf: 5069139 bytes, checksum: b64db0a7038e8010a2b92ce822daf969 (MD5) / Made available in DSpace on 2018-08-28T16:36:07Z (GMT). No. of bitstreams: 1 CELINA CÂNDIDA FERREIRA RODRIGUES – DISSERTAÇÃO (PPGMET) 2018.pdf: 5069139 bytes, checksum: b64db0a7038e8010a2b92ce822daf969 (MD5) Previous issue date: 2018-02-28 / CNPq / As florestas desempenham um papel importante na mitigação das mudanças climáticas, atuando como grandes armazenadoras de carbono por meio de sua produtividade primária. A produtividade primária bruta corresponde ao total de carbono fixado pela vegetação por meio do processo de fotossíntese. Neste sentido, o objetivo do trabalho foi avaliar a capacidade de fixação de carbono na bacia do rio Mogi-Guaçu, em especial nas áreas de cerrado e cana-de-açúcar no município de Santa Rita do Passa Quatro - SP, com base em estimativas efetivadas por meio de técnicas de sensoriamento remoto e proceder uma validação dos resultados segundo medidas realizadas pelo método da Eddy Coariance. Para a determinação da produtividade primária bruta foram determinados os balanços de radiação e energia por meio de imagens TM - Landsat 5 e OLI/TIRS - Landsat 8 utilizando a metodologia do SEBAL, para posterior comparação com a produtividade primária bruta do produto MOD17A2H e a estimada pelo método de eddy covariance. Foram selecionadas imagens sem presença de nuvens nos anos de 2005 e 2015, e empregadas as medições do fluxo de CO2 obtidas em duas torres micrometeorológicas instaladas em área de cana-de-açúcar e de Cerradão. As imagens Landsat proporcionaram maior concordância entre os dados de produtividade primária bruta em relação aos obtidos nas torres micrometeorológicas, diferentemente dos valores gerados com o MOD17A2H. A sazonalidade da produtividade primária bruta apresenta boa correspondência com os dados de precipitação pluviométrica registrados na área de estudo. O cerrado se comportou como sumidouro de carbono durante todo o ano, mesmo com precipitação abaixo da média, o que evidencia a necessidade de preservação deste bioma. / The forests play an important role in the mitigation of climate change by acting as large carbon sinks through their primary productivity. The gross primary productivity corresponds to the total carbon fixed by the vegetation through the photosynthesis process. In this way, the objective of this work was to evaluate the carbon fixation capacity in the Mogi-Guaçu river basin, especially in the cerrado and sugar cane areas in the municipality of Santa Rita do Passa Quatro - SP, based on estimates made by means of remote sensing techniques and validate the results according to measurements performed by the Eddy Coariance method. For the gross primary productivity determination, the radiation and energy balances were determined using TM - Landsat 5 and OLI / TIRS - Landsat 8 images using the SEBAL methodology, for further comparison with the gross primary productivity of the product MOD17A2H and the estimated by the eddy covariance method. Images were selected without clouds in the years 2005 and 2015, and measurements of the CO2 flux obtained in two micrometeorological towers installed in the area of sugarcane and Cerradão were used. The Landsat images provided greater agreement between the gross primary productivity data in relation to those obtained in the micrometeorological towers, unlike the values generated with the MOD17A2H. The seasonality of the gross primary productivity shows good correspondence with the rainfall data recorded in the study area. The cerrado has behaved as a carbon sink throughout the year, even with below-average precipitation, which it evidences the need for preservation of this biome.

abstract: Urbanization and woody plant encroachment, with subsequent brush management, are two significant land cover changes that are represented in the southwestern United States. Urban areas continue to grow, and rangelands are undergoing vegetation conversions, either purposely through various rangeland management techniques, or by accident, through inadvertent effects of climate and management. This thesis investigates how areas undergoing land cover conversions in a semiarid region, through urbanization or rangeland management, influences energy, water and carbon fluxes. Specifically, the following scientific questions are addressed: (1) what is the impact of different urban land cover types in Phoenix, AZ on energy and water fluxes?, (2) how does the land cover heterogeneity influence energy, water, and carbon fluxes in a semiarid rangeland undergoing woody plant encroachment?, and (3) what is the impact of brush management on energy, water, and carbon fluxes? The eddy covariance technique is well established to measure energy, water, and carbon fluxes and is used to quantify and compare flux measurements over different land surfaces. Results reveal that in an urban setting, paved surfaces exhibit the largest sensible and lowest latent heat fluxes in an urban environment, while a mesic landscape exhibits the largest latent heat fluxes, due to heavy irrigation. Irrigation impacts flux sensitivity to precipitation input, where latent heat fluxes increase with precipitation in xeric and parking lot landscapes, but do not impact the mesic system. In a semiarid managed rangeland, past management strategies and disturbance histories impact vegetation distribution, particularly the distribution of mesquite trees. At the site with less mesquite coverage, evapotranspiration (ET) is greater, due to greater grass cover. Both sites are generally net sinks of CO2, which is largely dependent on moisture availability, while the site with greater mesquite coverage has more respiration and generally greater gross ecosystem production (GEP). Initial impacts of brush management reveal ET and GEP decrease, due to the absence of mesquite trees. However the impact appears to be minimal by the end of the productive season. Overall, this dissertation advances the understanding of land cover change impacts on surface energy, water, and carbon fluxes in semiarid ecosystems. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2017