Aerial Dispersal Of Particles Emitted Inside Plant Canopies

This work combines numerical, experimental, and theoretical methods to investigate the dispersion of particles inside and above plant canopies. The large-eddy simulation (LES) approach is used to reproduce turbulence statistics and three-dimensional (3-D) particle dispersion within the canopy roughness sublayer (the region of flow significantly modified by the presence of the canopy, extending from ground to about three canopy heights). The Eulerian description of conservation laws of fluid momentum and particle concentration implies that the continuous concentration field is advected by the continuous flow field. Within the canopy, modifications are required for the filtered momentum and concentration equations, because spatial filtering of flow variables and concentration field is inapplicable to a control volume consisting of both fluid and solid elements. In this work, the canopy region is viewed as a space occupied by air only. The sink of airflow momentum induced by forces acting on the surfaces of canopy elements is parameterized as a non-conservative virtual body force that dissipates the kinetic energy of the air. This virtual body force must reflect the characteristic of the surface forces exerted by canopy elements within the control volume, and is parameterized as a "drag force" following standard practice in LES studies. Specifically, the "drag force" is calculated as a product of a drag coefficient, the projected leaf area density, and the square of velocity. Using a constant drag coefficient, this model allows first-order accuracy in reproducing the vertically integrated sink of momentum within the canopy layer for airflows of high Reynolds number. The corresponding LES results of first- and second-order turbulence statistics are in good agreement with experimental data obtained in the field interior, within and just above mature maize canopies. However, the distribution of momentum sink among weak (low velocity) and strong (high velocity) events has not been well reproduced, inferred from the significant underestition of streamwise and vertical velocity skewness as well as the fractions of vertical momentum flux transported by strong events. Using a velocity-dependent drag coefficient that accounts for the effect of plant reconfiguration (bending of canopy elements due to the aerodynamic drag force), the "drag force" model leads to LES results of streamwise and vertical velocity skewness as well as the fractions of vertical momentum flux transported by strong events in better agreement with field experimental data. Specifically, modeling the impact of reconfiguration allows strong events to penetrate into deeper canopy regions, reducing the underprediction of streamwise and vertical velocity skewness as well as the vertical momentum flux transported by strong events from 60%, 60%, and 40% to 5%, 20%, and 5%, respectively. On the other hand, the vertically integrated sink of momentum within the canopy layer has been kept approximately the same, so do first- and second-order turbulence statistics.The link between plant reconfiguration and turbulence dynamics within the canopy roughness sublayer is further investigated. The "reconfiguration drag model" using velocity-dependent drag coefficient is revised to incorporate a theoretical model of the force balance on individual crosswind blades. In the LES, the dimension and degree of the reconfiguration of canopy elements affect the magnitude and position of peak streamwise velocity skewness within the canopy as well as the fractions of vertical momentum flux transported by strong events. The streamwise velocity skewness is shown to be related to the penetration of strong events into the canopy, which is associated with the passage of canopy-scale coherent eddies. With the profile of mean vertical momentum flux constrained by field experimental data, changing the model of drag coefficient induces negligible changes in the vertically integrated "drag force" within the canopy layer. Consequently, first- and second-order turbulence statistics remain approximately the same. However, enhancing the rate of decrease of drag coefficient with increasing velocity increases the streamwise and vertical velocity skewness, the fractions of vertical momentum flux transported by strong events, as well as the ratio between vertical momentum flux transported by relatively strong head-down "sweeps" and relatively weak head-up "ejections". Note that "sweeps" and "ejections" are defined based on streamwise and vertical velocity fluctuations, and are different from their classical definitions. These results confirmed the inadequacy of describing the effects of canopy-scale coherent structures using just first- and second-order turbulence statistics.The filtered concentration equation is applied to the dispersion of particles within the canopy roughness sublayer, assuming that a virtual continuous concentration field is advected by a virtual continuous velocity field. A canopy deposition model is used to model the sink of particle concentration associated with the impaction, sedimentation, retention, and re-entrainment of particles on the surfaces of canopy elements. LES results of mean particle concentration field and mean ground deposition rate were evaluated against data obtained during an artificial continuous point-source release experiment. Accounting for the effect of reconfiguration by using a velocity dependent drag coefficient leads to better agreement between LES results and field experimental data of the mean particle concentration field, suggesting the importance of reproducing the distribution of momentum sink among weak and strong events for reproducing the dispersion of particles. LES results obtained using a velocity-dependent drag coefficient are analyzed to estimate essential properties for the occurrence of plant disease epidemics, i.e., the fraction of particles that escape the canopy (escape fraction) and the growth of the particle plume in the vertical direction. The most interesting finding is that an existing analytical function can be used to model the crosswind-integrated mean concentration field above the canopy normalized by the escape fraction for particles released from the field interior.Our LES results suggest that the escape fractions of particles released close to the canopy leading edge are greater than those released in the field interior, especially for particles released in the bottom half of the canopy. Effects of the canopy leading edge on the escape fraction can be tracked to the effects on the fractions of particles removed by deposition on modeled "canopy elements" and on the ground. The rate of deposition on canopy elements can be suppressed by enhanced modeled retention and re-entrainment of particles in the region of strong mean wind, while the rate of deposition on the ground can be suppressed by non-negligible mean vertical advection with respect to vertical turbulent transport. Away from the source, the vertical growth of the plume above the canopy-leading-edge area is slower than that above the field interior, due to greater shear of mean streamwise velocity in the internal boundary layer (IBL) than that in the fully-developed canopy roughness sublayer above the canopy.Spore dispersal downwind from the source field is investigated by representing the infected field as a prescribed constant mean concentration at a reference height near the canopy top. This "source-in-the-mean" model neglects the spatial heterogeneity of infections, release rates, and escape fractions, allowing a first-order accuracy in reproducing the effective source strength of a severely infected field. For dispersion of particles emitted from finite area sources in the atmospheric boundary layer (ABL), pre-existing theoretical models proposed for neutral conditions are extended to unstable conditions. The major effects of buoyancy are accounted for by modifying the profile of vertical velocity variance and considering the ratio between friction and convection velocities. Theoretical predictions of mean concentration profile, plume height, and horizontal transport above the source as well as ground deposition rate downstream from the source are in good agreement with LES results for the plume within the atmospheric surface layer.

The dispersal of pollen and spores by wind is central to some of the biggest challenges in science today, such as the spread of food-supply-threatening plant diseases; the rapid and widespread adoption of genetically modified (GM) plants in agriculture and their potential for pollen-mediated gene flow in the environment; and the presence and role of bioaerosols in cloud processes.Aerial Dispersal of Pollen and Spores is a unique, valuable, and comprehensive 432-page reference covering the many complex factors and effects encompassing the movement of spores through the air. It synthesizes material scattered across the literature of multiple disciplines in one single place—and adds many insights through new research in this important area of study. It uniquely emphasizes the critical, interacting biophysical processes that control the dispersal of particles in the atmosphere. By shining a greater light on these biophysical processes, scientists will get many new and valuable perspectives that can be applied to their research and to understanding models behind the spread of pathogens and genetic material in the atmosphere.Aerial Dispersal of Pollen and Spores serves as a valuable reference for researchers, graduate students, and advanced undergraduates in the fields of plant pathology, plant biology, meteorology, agronomy, and agricultural engineering. It is also well positioned as an important teaching resource across several disciplines, including plant pathology, botany, and aerobiology.

Plant disease epidemiology is a dynamic science that forms an essential part of the study of plant pathology. This book brings together a team of 35 international experts. Each chapter deals with an essential component of the subject and allows the reader to fully understand how each exerts its influence on the progress of pathogen populations in plant populations over a defined time scale. This edition has new, revised and updated chapters.

Many trace gases are exchanged between the atmosphere and the biosphere. Although much research has been published on the photosynthetic exchanges of carbon dioxide, oxygen, and water vapor, this book focuses on the importance of biogenic trace gases on atmosphere chemistry and ecosystem stability. Included are methane and its effect on the radiative properties of the atmosphere, hydrocarbons (isoprene and monoterpenes), and their role in the production of ozone and carbon monoxide. Also covered are sulfur and nitrogen gases, both of which can lead to ecosystem acidification. The biochemistry and physiology of production of these and other gases are investigated. Plant physiologists, ecologists, and atmospheric chemists and modelers will benefit from this book.

An introduction to the microbiology of bioaerosols and their impact on the world in which we live The microbiology of aerosols is an emerging field of research that lies at the interface of a variety of scientific and health-related disciplines. This eye-opening book synthesizes the current knowledge about microorganisms—bacteria, archaea, fungi, viruses—that are aloft in the atmosphere. The book is written collaboratively by an interdisciplinary and international panel of experts and carefully edited to provide a high-level overview of the emerging field of aerobiology. Four sections within Microbiology of Aerosols present the classical and online methods used for sampling and characterizing airborne microorganisms, their emission sources and short- to long-distance dispersal, their influence on atmospheric processes and clouds, and their consequences for human health and agro-ecosystems. Practical considerations are also discussed, including sampling techniques, an overview of the quantification and characterization of bioaerosols, transport of bioaerosols, and a summary of ongoing research opportunities in the field. Comprehensive in scope, the book: Explores this new field that is applicable to many disparate disciplines Covers the emission of bioaerosols to their deposit, covering both quantitative and qualitative aspects Provides insights into social and environmental effects of the presence of bioaerosols in the atmosphere Details the impact of bioaerosols on human health, animal and plant health, and on physical and chemical atmospheric processes Written by authors internationally recognized for their work on biological aerosols and originating from a variety of scientific fields collaborated on, Microbiology of Aerosols is an excellent resource for researchers and graduate or PhD students interested in atmospheric sciences or microbiology.

The treetops of the world's forests are where discovery and opportunity abound, however they have been relatively inaccessible until recently. This book represents an authoritative synthesis of data, anecdotes, case studies, observations, and recommendations from researchers and educators who have risked life and limb in their advocacy of the High Frontier. With innovative rope techniques, cranes, walkways, dirigibles, and towers, they finally gained access to the rich biodiversity that lives far above the forest floor and the emerging science of canopy ecology. In this new edition of Forest Canopies, nearly 60 scientists and educators from around the world look at the biodiversity, ecology, evolution, and conservation of forest canopy ecosystems. Comprehensive literature list State-of-the-art results and data sets from current field work Foremost scientists in the field of canopy ecology Expanded collaboration of researchers and international projects User-friendly format with sidebars and case studies Keywords and outlines for each chapter

Most branches of science have what might be termed a 'core area' which is both related to and helps to integrate peripheral topics to form the overall subject area. Without this central link, the subject is simply a collection of disparate, albeit gener ally related topics. What genetics is to plant breeding, epidemiology is to the subject of plant pathology and, no matter what individual topic is considered, it is always possible to recognize the interaction with and relationship to epidemiological factors. Broadly speaking, until the 1950s, plant pathology was considered as the applied side of mycology and, indeed, the British Society of Plant Pathology was spawned from its mentor, the British Mycological Society, with considerable help from The Association of Applied Biology. However, with the exploding world popu lation and the growing demand for food, plant pathologists became increasingly aware of the need for a more considered, measured, precise and even holistic approach to their subject and, particularly, to plant disease management. Looking back over 40 years of teaching and research in plant pathology, it was very clear that the 'core' of the subject was epidemiology and that this 'new' study was developing a very distinct identity which was rapidly being recognized in its own right. The 'shotgun' approach to plant disease 'control' was quickly perceived to be too inexact and almost every aspect of the subject was being reviewed, refined and advanced.