Vertical diffusion of pollutants in the atmospheric boundary layer

An atmospheric diffusion model is used to study the main features of vertical distribution of pollutants released from a continuous point source at different heights in a thermally stratified atmospheric boundary layer. The model is based on the two-dimensional advection-diffusion-deposition equation, with vertical profiles of wind and eddy diffusivity for the atmospheric boundary layer. The formulation permits studying the influence of surface roughness, atmospheric stability, mixing depth and source height on concentration distributions. Numerical simulations of atmospheric diffusion experiments are done. From the two-dimensional concentration fields, different para-meters are calculated in terms of the second, third and fourth order statistical moments which characterize vertical distributions of material. The computed values are satisfactorily compared with those evaluated from observational data. The vertical dispersion coefficient (second order moment root mean square) is also compared with those proposed by other authors.Se utiliza un modelo de difusión atmosférica para analizar las características principales de la distribución vertical de contaminantes emitidos en forma continua, desde diferentes alturas, en una capa límite atmosférica térmicamente estratificada. El modelo se basa en la ecuación bidimensional de advección-difusión-depósito, con perfiles verticales del viento y la difusividad turbulenta válidos para la capa límite atmosférica. La formulación permite analizar la influencia de la rugosidad del terreno, la estabilidad atmosférica y las alturas de la capa de mezcla y de la emisión de contaminantes sobre las distribuciones de la concentración. Se realiza la simulación numérica de experimentos de difusión atmosférica y a partir de los campos bidimensionales de concentración obtenidos, se calculan diferentes parámetros en función de momentos estadísticos de segundo, tercero y cuarto orden, para caracterizar las distribuciones verticales del material. Los valores hallados se comparan satisfactoriamente con los resultantes de los datos observacionales. El coeficiente de dispersión vertical (raíz cuadrada del momento de segundo orden), se compara además con los propuestos por otros autores.Material digitalizado en SEDICI gracias a la colaboración de la Facultad de Ciencias Astronómicas y Geofísicas (UNLP).Asociación Argentina de Geofísicos y Geodesta

Dispersión de contaminantes emitidos desde superficie en una capa límite atmosférica estratificada neutralmente

El proceso de la contaminación atmosférica puede ser resumido en tres etapas principales: emisión-transporte y difusión de contaminantes-contacto con receptores. Un modelo de difusión atmosférica permite relacionar la concentración de los contaminantes en el aire con su intensidad de emisión. En este trabajo se presenta un modelo de advección-difusión de contaminantes emitidos desde superficie en una capa limite neutralmente estratificada, resuelto mediante métodos numéricos. El perfil vertical del viento en la capa es obtenido a partir de la aplicación de la hipótesis del transporte-gradiente y de una forma funcional de la difusividad turbulenta hallada experimentalmente. El modelo incluye esas expresiones, y sus resultados son comparados satisfactoriamente con datos observacionales y con los obtenidos mediante otros procedimientos. Asimismo, se obtienen valores de parámetros utilizados en modelos operativos de difusión atmosférica.Air pollution process may be summarized into emission-atmospheric transport and diffusion-receptors. An atmospheric diffusion model relates air pollution three main steps: concentration with emission rates. In this paper an advection-diffusion model for ground level emissions and in neutral stratified atmospheric boundary layer conditions is solved by numerical techniques. The wind profile in the atmospheric boundary layer is obtained from the gradient-transfer hyphotesis combining with a diffusion coefficient empirical profile. These profiles are included in the model. The results are in reasonable agreement with observational data and with other models. Furthermore, several parameters used in operational atmospheric diffusion models are obtained.Asociación Argentina de Geofísicos y Geodesta

Dispersión de contaminantes emitidos desde una fuente elevada y continua en la capa limite atmosférica

Uno de los objetivos de la meteorología aplicada a la contaminación del aire es la predicción de la dispersión de los contaminantes. Los modelos de calidad del aire permiten estimar cuantitativamente la difusión atmosférica relacionando las emisiones de contaminantes con sus concentraciones en el aire. En este trabajo se considera el caso de una emisión continua de contaminantes desde una fuente elevada en una capa límite atmosférica estratificada térmicamente. El modelo propuesto utiliza la ecuación bidimensional semiempírica de difusión-advección con perfiles verticales del viento y de la difusividad turbulenta que permiten incluir las condiciones de estabilidad atmosférica y las características del terreno. Mediante métodos numéricos de resolución se obtiene la distribución espacial de la concentración de los contaminantes en el aire, para diferentes alturas de emisión, condiciones meteorológicas y topográficas. Por su interés práctico, se analiza la influencia de los factores mencionados sobre la concentración en superficie a distintas distancias de la fuente. Las concentraciones obtenidas se comparan con las que predice el modelo gaussiano. Los resultados indican un comportamiento satisfactorio del modelo propuesto.Air quality models transform pollutant emissions into concentrations. In this paper, the continuous emissions of pollutants from elevated sources in a thermically stratified atmospheric boundary layer are considered. The model consists of the bidimensional semiempirical advection-diffusión equation with vertical profiles of the wind and turbulent diffusivity which allow to include stability conditions and roughness. The spatial distribution of concentrations is obtained from numerical methods for different emission heights and meteorological and topographical conditions. The influence of these factors on the ground level concentration is analized. Concentrations obtained are compared with those predicted by the Gaussian model. The results show an acceptable behavior of the proposed model.Asociación Argentina de Geofísicos y Geodesta

Regional Pollution due to Biomass Burning in South America

The present study analyses a low level jet event that occurred inconjunction with biomass burning and focuses on the impact onsoutheastern South America. The aerosol transport is analyzed usingoutputs of the CATT-BRAMS modeling system. The relationships betweenthe low level jet and the smoke plume pattern and concentrations are shown.The present study analyses a low level jet event that occurred inconjunction with biomass burning and focuses on the impact onsoutheastern South America. The aerosol transport is analyzed usingoutputs of the CATT-BRAMS modeling system. The relationships betweenthe low level jet and the smoke plume pattern and concentrations are shown

Distribution of Ophioglossum reticulatum L. in South America. A case of long-distance jump dispersal?

The objective of this exploratory work is to test the hypothesis that South American populations of Ophioglossum reticulatum L. derive from Africa. Spores cross the Atlantic transported by wind and arrive in South America in recurrent migration. Three-dimensional (backward and forward) trajectories of spores between Africa and South America were calculated using the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT4). The model showed possible backward trajectories in the low troposphere arriving in South America with probable origin in Northwestern Africa. The results support the hypothesis of long-distance dispersal of the studied species. Including vertical motion in the model runs allowed obtaining valuable and novel information about the migration routes. The trade winds combined with the South American monsoon could be a dispersal vehicle for the disseminules from Northwestern Africa to the eastern slopes of the Andes. As the monsoon is a periodic regional atmospheric circulation pattern, transcontinental migration can be assumed to be a recurring phenomenon that provides genetic exchange and prevents speciation by reproductive isolation. Modelled forward trajectories connect the neotropics with Africa-Madagascar, but they seem to be less effective due to their travelling altitudes. This hypothesis might explain the absence of infraspecific taxa restricted to different geographic locations.Facultad de Ciencias Naturales y Muse

Distribution of Ophioglossum reticulatum L. in South America : A case of long-distance jump dispersal?

Fil: Meza Torres, Esteban I.. Instituto de Botánica del Nordeste. CONICET-UNNE. Corrientes; ArgentinaFil: Cerne, Bibiana. Departamento de Ciencias de la Atmósfera y los Océanos. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires; ArgentinaFil: Ulke, Ana G.. Departamento de Ciencias de la Atmósfera y los Océanos. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires; ArgentinaFil: Morbelli, Marta Alicia. Cátedra de Palinología. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; Argentin

Examining the influence of meteorological simulations forced by different initial and boundary conditions in volcanic ash dispersion modelling

Abstract: The performance of the combination of the Fall3D ash dispersion model with the Weather Research and Forecast (WRF) meteorological model in the southern cone of South America under two initial and boundary conditions was evaluated. ERA-Interim and NCEP-GFS databases were used as dynamic conditions by WRF to simulate meteorological fields for FALL3D. As a case study, we used the eruption of the Puyehue-Cordón Caulle Volcanic Complex occurred in Chile in June 2011. The simulated meteorological results were compared with the horizontal wind direction, meridional and zonal wind components, air and dew point temperatures of 7 radio sounding stations using a set of error indicators. In addition, the ash mass load simulated by FALL3D for a day of maximum dispersion of volcanic ash was evaluated using the Moderate Resolution Imaging Spectroradiometer (MODIS), on which the Prata algorithm was applied. As well as this, the WRF dominant physical processes with both dynamic conditions were analyzed for that same date. Meteorological results indicated that the simulation performed with WRF and NCEPGFS shows the lowest errors at levels between 925 hPa and 300 hPa. Ash dispersion simulated with FALL3D and WRF in both dynamic conditions shows a different perfomance, which from the synoptic and dynamic viewpoint can be explained for the result of wind intensity and geopotential height. Moreover, WRF intiliazed with NCEPGFS and FALL3D has a higher degree of concordance with the MODIS image. Based on the analysis and results, it was concluded that for the southern cone of South America: 1) it was not trivial for the simulation of volcanic ash dispersion to use one dynamic condition or another in WRF; 2) in that sense, meteorological variables that influenced the differences in volcanic ash dispersion were horizontal wind intensity and direction and geopotential heights; 3) the system generated from the combination of the WRF model initialized with NCEP-GFS and the FALL3D dispersion model would provide better estimations of ash plume position and deposition in the regio