No description available.

This PhD thesis investigates the transport and distribution of short-lived halogenated organic substances in the tropical tropopause layer (TTL) in the Pacific Ocean. Short-lived halocarbons are one of the major groups of the ozone depleting substances as they provide a source for the active halogens which decrease ozone in the atmosphere. The TTL serves as the primary gateway of tropospheric air to enter the stratosphere. The air which enters the stratosphere is distributed all over the globe. Thus, the research on which tropospheric air masses go into the TTL, its structure and composition and the transport within is crucial. This thesis uses the UK Meteorological Office Lagrangian particle dispersion model NAME to (i) support the flight planning activities and achieve the multi aircraft coordination in CAST, CONTRAST, ATTREX 2014 campaigns, and (ii) quantify the amount and distribution of short-lived halocarbons in the TTL, and explain differences in these vertical distributions and transport characteristics. The halocarbons of interest are methyl iodide (CH3I), bromoform (CHBr3) and dibromomethane (CH2Br2). A new NAME procedure was developed and operated successfully to provide routine simulations and near real-time products suitable for guiding the CAST, CONTRAST and ATTREX aircraft in order to achieve their mission scientific objectives, and to make coordinated measurements. NAME was used post-campaign to analyse distribution of short-lived halocarbons in the TTL, identify their source regions and transport timescales. A new approach is proposed to investigate the TTL composition in terms of the boundary layer air influence, and subsequently quantify CH3I, CHBr3 and CH2Br2 by estimating their boundary layer and background contribution. The sums of these modelled estimates are in good agreement with the ATTREX 2014 and 2013 CH3I, CHBr3 and CH2Br2 observations. The quantification of the contribution of short-lived bromocarbons to the active bromine in the TTL was achieved, and the results lie within the range of the recent literature studies. The final focus of this thesis is on how well NAME represents the particle displacement via convection. Convection is the major transport pathway for the short-lived halocarbons to reach the TTL. The role of convection in transporting CH3I, CHBr3 and CH2Br2 to the TTL is assessed using the new convection scheme in NAME. A validation of the performance of this scheme is provided, showing that it yields improved and more realistic representation of the particle displacement via convection.

The upper troposphere-lower stratosphere (UTLS) is a transition region between the troposphere and the stratosphere. During the boreal summer, the UTLS is dominated by large-scale anticyclonic circulations over the Asian and North American monsoon regions, exhibiting complex dynamical and chemical characteristics. Re-cent studies have emphasized the important role of the summer monsoon systemin stratosphere-troposphere exchange of water vapor and chemical species, which strongly influences the atmospheric chemistry and climate system. The transport in the UTLS region occurs in both directions, stratosphere-troposphere transport (STT)and troposphere-stratosphere transport (TST). For example, observational studies indicate localized maxima of tropospheric pollutants and stratospheric water vapor(SWV) in the UTLS, which are controlled by deep convection and large-scale circulation. Meanwhile, stratospheric ozone (O3) can fold into tropospheric air and entrain into the planetary boundary layer (PBL) via deep STT, and thus affect air quality at the surface. In this thesis, we aim at improving the understanding of the transport processes in the UTLS that are linked to monsoon dynamics using observations and modelling tools.<div><br></div><div>First, we investigate the TST transport in association with the Asian summer monsoon. We examine the simulation of SWV in the Community Earth System Model, version 1 with the Whole Atmosphere Community Climate Model as its atmospheric component [CESM1(WACCM)]. CESM1(WACCM) generally tends to simulate a SWV maximum over the central Pacific Ocean instead of over the Asian continent as observed, but this bias is largely improved in the high vertical resolution version. The high vertical resolution model with increased vertical layers in the UTLS is found to have a less stratified UTLS over the central Pacific Ocean compared with the low vertical resolution model. It therefore simulates a steepened potential vorticity gradient over the central Pacific Ocean that better closes the upper-level anticyclone and confines the SWV within the enhanced transport barrier.<br></div><div><br></div><div>We further study the transport pathways connecting the Northern Hemisphere sur-face and the North American (NA) UTLS by diagnosing Boundary Impulse Response idealized tracers implemented at the Northern Hemisphere surface during summer. In ensemble average, air masses enter the NA UTLS region above Central America, and then slowly mix into the higher latitudes. However, fast transport pathways with modal age around two weeks are evident in some tracer ensembles. For these rapid transport pathways, the tracers first reach the UTLS region over the eastern Pacific and the Gulf of Mexico as a result of enhanced deep convection and vertical advection, followed by horizontal transport over the United States by a strengthened UTLS anticyclone circulation.<br></div><div><br></div><div>To the end, we evaluate the downward transport of stratospheric O3via STT using simulation from a state-of-the-art chemistry climate model implemented with an artificial stratospheric ozone tracer (O3S). We find that O3transported from the stratosphere makes a significant contribution to the surface O3variability where back-ground surface O3exceeds 95thpercentile, especially over the western U.S. Maximum covariance analysis is applied to O3anomalies paired with stratospheric O3traceranomalies to identify the stratospheric intrusion and the underlying dynamical mechanism. The first leading mode corresponds to deep stratospheric intrusions in the western and northern tier of the U.S., and intensified north easterlies in the mid-to-lower troposphere along the west coast, which also facilitate the transport to the eastern Pacific Ocean. The second leading mode corresponds to deep intrusions over the Intermountain Regions. Both modes are associated with eastward propagating baroclinic systems, which are amplified near the end of the North Pacific storm tracks, leading to strong descents over the western United States.<br></div>

Fusarium head blight (FHB), caused by Fusarium graminearum, is a serious disease of wheat and barley that has caused several billion dollars in crop losses over the last decade in the United States. Spores of F. graminearum are released from corn and small grain residues left-over from the previous growing season and are transported long distances in the atmosphere before being deposited.  Current risk assessment tools consider environmental conditions favorable for disease development, but do not include spore transport. Long distance transport models have been proposed for a number of plant pathogens, but many of these models have not been experimentally validated. In order to predict the atmospheric transport of F. graminearum, the potential source strength (Qpot) of inoculum must be known.  We conducted a series of laboratory and field experiments to estimate Qpot from a field-scale source of inoculum of F. graminearum.  Perithecia were generated on artificial (carrot agar) and natural (corn stalk) substrates.  Artificial substrate (carrot agar) produced 15±0.4 perithecia cm-2, and natural substrate (corn stalk) produced 44±2 perithecia cm-2.  Individual perithecia were excised from both substrate types and allowed to release ascospores every 24 hours.  Perithecia generated from artificial (carrot agar) and natural (corn stalk) substrates released a mean of 104±5 and 276±16 ascospores, respectively.  A volumetric spore trap was placed inside a 3,716 m2 clonal source of inoculum in 2011 and 2012.  Results indicated that ascospores were released under field conditions predominantly (>90%) during the night (1900 to 0700 hours).  Estimates of Qpot for our field-scale sources of inoculum were approximately 4 billion ascospores per 3,716 m2.  Release-recapture studies were conducted from a clonal field-scale source of F. graminearum in 2011 and 2012. Microsatellites were used to identify the released clone of F. graminearum at distances up to 1 km from the source. Dispersal kernels for field observations were compared to results predicted by a Gaussian dispersal-based spore transport model.  In 2011 and 2012, dispersal kernel shape coefficients were similar for both results observed in the field and predicted by the model, with both being dictated by a power law function, indicating that turbulence was the dominant transport factor on the scale we studied (~ 1 km).  Model predictions had a stronger correlation with the number of spores being released when using a time varying q0 emission rate (r= 0.92 in 2011 and r= 0.84 in 2012) than an identical daily pattern q0 emission rate (r= 0.35 in 2011 and r= 0.32 in 2012).  The actual numbers of spores deposited were 3 and 2000 times lower than predicted if Qpot were equal to the actual number of spores released in 2011 and 2012, respectively. Future work should address estimating the actual number of spore released from an inoculated field during any given season, to improve prediction accuracy of the model.  This work should assist in improving current risk assessment tools for FHB and contribute to the development of early warning systems for the spread of F. graminearum. / Ph. D.

Stratosphere Troposphere exchange (STE) is important to study as it controls the chemical composition of the upper troposphere/lower stratosphere (UTLS) and thus the radiative balance of this region. STE also controls the transport of chemicals into the stratosphere which are vital to ozone depletion. The troposphere and the stratosphere have specific chemical characteristics and the transition region between these regions displays characteristics of both. Ozone and water vapour concentrations can be used as tracers for the characteristics of the troposphere and stratosphere. This thesis develops measures in tracer space, which allow the determination of the strength and depth of atmospheric mixing between the troposphere and the stratosphere in extratropical regions. The application of entropy as a measure of atmospheric mixing as introduced by Patmore and Toumi [2006], is improved in this study. This is a measure of how the ozone and water vapour mixing ratios vary as a result of mixing. An additional metric to give further information on the form of the mixing line in tracer space is also developed. This measure uses the ozone and water vapour mixing ratios at the boundaries of the transition region (BO3 and BH2O). This study uses data from ozonesondes and hygrometers, along with satellite data from the Atmospheric Infrared Sounder (AIRS). The ozone product from AIRS is also validated as part of this study. The entropy, BO3 and BH2O measures from this study, are successfully shown to detect regions of enhanced mixing in comparison studies. A key comparison shows that the measures developed in this study are able to produce comparable conclusions to higher resolution aircraft data, with regards to mixing. The separation of entropy, BO3 and BH2O, into different categories allows mixing processes to be assigned to some of the categories. Mixing is shown to have geographic preference, with some regions having significantly more mixing. Some categories have preference with regards to their location either poleward or equatorward of the jet stream. In addition, some information as to the direction of the vertical transport, whether stratosphere to troposphere or vice versa, is obtained.

Perfluoroalkyl acids (PFAAs) are man-made chemicals which have been observed in the global environment, even in locations far away from where they are emitted. These persistent substances are taken up in humans and biota and may have toxic effects. Knowledge about how PFAAs are dispersed in the environment is needed to discern strategies to manage their sources and to evaluate the efficacy of adopted legislation. This thesis aimed to increase our understanding of the sources of PFAAs to the atmosphere and how PFAAs are transported in air. The results of Paper I demonstrated that gaseous perfluorooctanoic acid (PFOA) sorbs to typical glass fibre filters (GFFs) used in high-volume air sampling of PFAAs. As a consequence, the fraction of gaseous PFOA present in sampled air is underestimated, while the fraction of PFOA associated with aerosols is overestimated. Replacing GFFs with filters deactivated through silanisation and siliconisation did not eliminate this sampling artefact and is therefore not recommended as a means to determine the gas-particle partitioning of PFAAs. In Paper II, monitoring of the mass of PFOA transferred from water solutions of pH 0.2-5.5 demonstrated that the acid dissociation constant of linear PFOA and the four most ubiquitous branched PFOA isomers is around or below 1. Furthermore, the results demonstrated that the presence of counter ions and organic matter in water retarded, rather than enhanced, the volatilisation of PFOA. Therefore, volatilisation of all isomers of PFOA from environmental waters is expected to be negligible. To further study the transfer of PFAAs from environmental waters to air, Paper III simulated the process of sea spray generation in the laboratory. Strong enrichment of PFAAs was observed from bulk water to the surface microlayer and to aerosols. The enrichment increased with PFAA chain length, indicating that this process is of greater importance for more surface active substances. The highest enrichment was observed in aerosols &lt; 1.6 µm, which can travel over long distances if not rained out. Based on the measured aerosol enrichment factors we estimated that approximately 70 metric tonnes of PFAAs are aerosolised from the global oceans yearly and that 3% of this mass is deposited in terrestrial environments. Paper IV reported the occurrence of branched PFOA isomers in deposition sampled in five geographical locations. The presence of these isomers demonstrated that atmospheric transformation of fluorotelomer alcohols is not the only ongoing source of PFAAs to air. We hypothesised that, additionally, both sea spray aerosols and direct emissions from manufacturing sources contributed to the contamination of the precipitation on different spatial scales. Although further research is required to determine the relative importance of different sources to the atmosphere locally and globally, this thesis has substantially advanced the state-of-the-science by i) demonstrating the significance of an air sampling artefact discussed as an uncertainty in the scientific literature over the past decade, ii) definitively ruling out volatilisation from environmental waters as a source of PFOA to air, iii) demonstrating transfer of PFAAs from seawater to air via sea spray aerosols and thus quantifying the environmental importance of this process, and iv) ultimately demonstrating that several types of sources of PFAAs impact the global atmosphere and thus PFAA contamination patterns in precipitation. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

Aerosols change the Earth's energy balance. Black carbon (BC) aerosols are a product of incomplete combustion of fossil fuels and biomass burning and cause a net warming through aerosol radiation interactions (ari) and aerosol cloud interactions (aci). BC aerosols have potentially strong implications on the Arctic climate, yet the net global climate effect of BC is very uncertain. Best estimates assume a net warming effect, roughly half to that of CO2. However, the time scales during which CO2 emissions affect the global climate are on the order of hundreds of years, while BC is a short-lived climate pollutant (SLCP) with atmospheric life times of days to weeks. Climate models or atmospheric transport models struggle to emulate the seasonality and amplitude of BC concentrations in the Arctic, which are low in summer and high in winter/spring during the so called Arctic haze season. The high uncertainties regarding BC's climate impact are not only related to ari and aci, but also due to model parameterizations of BC lifetime and transport, and the highly uncertain estimates of global and regional BC emissions. Given the high uncertainties in technology-based emission inventories (EI), there is a need for an observation-based assessment of sources of BC in the atmosphere. We study short-term and long-term observations of elemental carbon (EC), the mass-based analog of optically-defined BC. EC aerosol concentrations and carbon-isotope-based (δ13C and ∆14C) sources were constrained (top-down) for three Arctic receptor sites in Abisko (northern Sweden), Tiksi (East Siberian Russia), and Zeppelin (on Svalbard, Norway). The radiocarbon (∆14C) signature allows to draw conclusion on the EC sources (fossil fuels vs. biomass burning) with high accuracy (&lt;5% variation). Stable carbon isotopic fingerprints (δ13C) give qualitative information of the consumed fuel type, i.e. coal, C3-plants (wood), liquid fossil fuels (diesel) or gas flaring (methane and non-methane hydrocarbons). These fingerprints can be used in conjunction with Bayesian statistics, to estimate quantitative source contributions of the sources. Finally, our observations were compared to predictions from a state of the art atmospheric transport model (coupled to BC emissions), conducted by our collaborators at NILU (Norwegian Institute for Air Research). Observed BC concentrations showed a high seasonality throughout the year, with elevated concentrations in the winter, at all sites. The highest concentrations were measured on Svalbard during a short campaign (Jan-Mar 2009) focusing on BC pollution events. Long-term observations showed that Svalbard (2013) had overall the lowest annual BC concentrations, followed by Abisko (2012) and Tiksi (2013). Isotope constraints on BC combustion sources exhibited a high seasonality and big amplitude all across the Eurasian Arctic. Uniform seasonal trends were observed in all three year-round studies, showing fractions of biomass burning of 60-70% in summer and 10-40% in winter. Europe was the major source region (&gt;80%) for BC emissions arriving at Abisko and the main sources were liquid fossil fuels and biomass burning (wood). The model agreed very well with the Abisko observations, showing good model skill and relatively well constrained sources in the European regions of the EI. However, for the Svalbard and East Siberian Arctic observatories the model-observation agreement was not as good. Here, Russia, Europe and China were the major contributors to the mostly liquid fossil and biomass burning BC emissions. This showed that the EI still needs to be improved, especially in regions where emissions are high but observations are scarce (low ratio of observations to emitted pollutant quantity). Strategies for BC mitigation in the (Eurasian) Arctic are probably most efficient, if fossil fuel (diesel) emissions are tackled during winter and spring periods, all across Eurasia. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript.</p>

Este trabalho trata do estudo do transporte atmosférico de emissões de queimadas na região Amazônica e Centro-Oeste do Brasil. Em consequência da queima de biomasa, gases (CO IND.2, CO, CH IND.4, etc.) e partículas são emitidas para a atmosfera, os quais podem provocar mudanças no equilíbrio climático e biogeo químico do planeta Terra, em várias escalas. O estudo é realizado por meio de simulação numérica dos movimentos da atmosfera utilizando o modelo atmosférico RAMS (Regional Atmospheric Modeling System). São utilizados os métodos Lagrangiano e Euleriano. No método Langrangiano o transporte é estudado por meio do cálculo de trajetórias cinemáticas 3d de massas de ar, utilizando o campo de vento simulado, na escala resolvida. A posição inicial das massas de ar é obtida a partir de mapas de queimadas detectadas por sensores a bordo de satélites como o AVHRR da série NOAA. Uma metodologia simples que contabiliza os efeitos de processos convectivos úmidos da escala sub-grade na velocidade vertical da parcela de ar para modelo atmosféricos de baixa resolução, é introduzida no modelo de trajetórias. No método Euleriano, é resolvida a equação de conservação de massa dos principais elementos emitidos. Para tanto é introduzido um modelo de fontes emissoras de gases/partículas associadas à queimadas em floresta tropical e cerrado da América do Sul, distribuídas espacial e temporalmente através da assimilação diária de mapas de posição de queimadas produzidos por sensoriamento remoto. Os termos de advecção na escala resolvida e o transporte turbulento na escala sub-grade são resolvidos utilizando as parametrizações próprias do modelo RAMS. É introduzida uma parametrização do transporte sub-grade associado às circulações úmidas e profundas não resolvidas explicitamente pelo modelo, devido a baixa resolução espacial. Termos sumidouros associados a processos genéricos de remoção/transformação de gases/partículas são ) também parametrizadas e inseridos na equação de conservação de massa. A metodologia é aplicada a um estudo de caso ocorrido no mês de julho de 1993. São modelados o transporte turbulento na camada limite planetária, os efeitos transientes associados à entrada de frentes frias vindo do sul do continente e à convecção na bacia Amazônica no transporte convectivo de poluentes, bem como o transporte associado aos sistemas de larga escala. São observados padrões de exportação continental de poluentes, com saídas ocorrendo a noroeste da América do Sul em direção ao oceano Pacífico, e a sudeste em direção ao oceano Atlântico. / A study about the atmospheric transport f biomass burning emissions in the Amazon and the Central of Brazil is presented. Gases (CO IND.2, CO, CH IND.4, etc.) and particles emitted to the atmosphere due the biomass burning are responsible for the climatic and biogeochemical budget changes in the Earth planet, in many scales. This study is carried out through a numerical simulation of the atmospheric motions using the atmospheric models RAMS (Regional Atmospheric Modeling System). Lagragian and Eulerian methods are used. In the Lagrangian method the transport is studied through 3D kinematic air mass trajectories calculation, using simulated wind fields, in a resolved scale. The initial position of the air masses is obtained from biomass burning spots maps, derived from satellite sensors (AVHRR from NOAA series). A simple methodology to take into account the sub-grid effects of wet convective process in the vertical velocity of the air parcels, for low resolution atmospheric models is introduced in the trajectory model. In the Eulerian method the mass conservation equation is resolved for the main elements emitted. A model of gases and particles sources emissions is introduced associated with biomass burning in South America tropical forest and savanna, spatially and temporally distributed and daily assimilated, according to the biomass burning spots defined by remote sensing. The advection in a resolved scale and turbulent transport, in a sub-grid parameterization associated to wet and deep circulation not explicitly resolved by the model due its low spatial resolution is introduced. Sinks associated with generic process of removal/transformation of gases/particles are parameterized and introduced in the mass conservation equation. The methodology is applied to a case study on July 1993. The turbulent transport in the planetary boundary layer the transient effects in the convective transport of pollutants associated with cold fronts from the south and convection in the Amazon basin and the transport associated with the large scale systems are modeled. Patterns of pollutant exportation are observed with a corridor to the Pacific Ocean in the South America Northwest and another in the Southeast to the Atlantic Ocean.

The recent emergence of highly virulent strains of the pathogen causing wheat stem rust has been acknowledged as a threat to global food security. In infected wheat fields, vast amounts of pathogenic fungal spores are produced that can be carried away by wind. For targeted disease surveillance and control it is important to estimate when, where and how many fungal spores are dispersed from infected to susceptible wheat fields. In this study, high-performance computational resources are used to investigate long-distance dispersal revealing atmospheric pathways that connect entire continents. Mechanistic simulations of turbulent atmospheric spore dispersal are conducted. The analyses bring together a variety of data, including international field disease surveys and finely resolved meteorological model data. The UK Met Office's Langrangian stochastic particle dispersion model, NAME, is applied, extended and coupled to other models in a set of case studies. In the first case study, spore dispersal is analysed across Southern/East Africa, the Middle East, and Central/South Asia by simulating billions of stochastic trajectories of fungal spores over dynamically changing host and environmental landscapes. The circumstances under which virulent strains, such as Ug99, pose a risk to globally important wheat producing areas are identified. Simulation results indicate a negligible risk for dispersal from key wheat producing countries on the East African continent (Ethiopia, Kenya) directly to India and Pakistan. However, there is a considerable risk for atmospheric transport from the Arabian Peninsula to South Asia. Spore dispersal trends are quantified between all countries in the domain providing estimates which can be used to improve targeted sampling and control. In the second case study, dispersal from southern Africa to Australia is analysed. Simulation results, as well as data from phenotypic and genotypic analyses, support the hypothesis that extremely long-distance airborne dispersal across the Indian Ocean is possible, albeit rare. This indicates that the pathogen populations on the two continents are connected and underlines the importance of sharing surveillance intelligence between continents. The third case study focusses on Ethiopia, determining likely origins of strain TKTTF that recently caused severe epidemics in East Africa's largest wheat producing country. The analyses suggest inflow into Ethiopia from the Middle East via Yemen, consistent with field survey data. The risk for inflow of pathogens into Ethiopia from key neighbouring countries is ranked for different months of the wheat season. In the last results chapter a pilot study is summarized testing the feasibility of an automated short-term forecasting system for spore dispersal from the latest field disease detection sites. Whilst the functionality and practical relevance of the forecasting system is demonstrated, considerable challenges remain for testing the forecasts. The predictive simulation framework described in this thesis can be applied to any wheat producing area worldwide to assess dispersal risks. The research has broader relevance because long-distance dispersal is a key mechanism for the transmission of several crop and livestock diseases, and also plays an important role in other areas of ecology.

Stratosphere Troposphere exchange (STE) is important to study as it controls the chemical composition of the upper troposphere/lower stratosphere (UTLS) and thus the radiative balance of this region. STE also controls the transport of chemicals into the stratosphere which are vital to ozone depletion. The troposphere and the stratosphere have specific chemical characteristics and the transition region between these regions displays characteristics of both. Ozone and water vapour concentrations can be used as tracers for the characteristics of the troposphere and stratosphere. This thesis develops measures in tracer space, which allow the determination of the strength and depth of atmospheric mixing between the troposphere and the stratosphere in extratropical regions. The application of entropy as a measure of atmospheric mixing as introduced by Patmore and Toumi [2006], is improved in this study. This is a measure of how the ozone and water vapour mixing ratios vary as a result of mixing. An additional metric to give further information on the form of the mixing line in tracer space is also developed. This measure uses the ozone and water vapour mixing ratios at the boundaries of the transition region (BO3 and BH2O). This study uses data from ozonesondes and hygrometers, along with satellite data from the Atmospheric Infrared Sounder (AIRS). The ozone product from AIRS is also validated as part of this study. The entropy, BO3 and BH2O measures from this study, are successfully shown to detect regions of enhanced mixing in comparison studies. A key comparison shows that the measures developed in this study are able to produce comparable conclusions to higher resolution aircraft data, with regards to mixing. The separation of entropy, BO3 and BH2O, into different categories allows mixing processes to be assigned to some of the categories. Mixing is shown to have geographic preference, with some regions having significantly more mixing. Some categories have preference with regards to their location either poleward or equatorward of the jet stream. In addition, some information as to the direction of the vertical transport, whether stratosphere to troposphere or vice versa, is obtained.