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

Resting EEG Measures Of Brain Arousal In A Multisite Study Of Major Depression

Several studies have found upregulated brain arousal during 15-minute EEG recordings at rest in depressed patients. However, studies based on shorter EEG recording intervals are lacking. Here we aimed to compare measures of brain arousal obtained from 2-minute EEGs at rest under eyes-closed condition in depressed patients and healthy controls in a multisite project—Establishing Moderators and Biosignatures of Antidepressant Response for Clinical Care (EMBARC). We expected that depressed patients would show stable and elevated brain arousal relative to controls. Eighty-seven depressed patients and 36 healthy controls from four research sites in the United States were included in the analyses. The Vigilance Algorithm Leipzig (VIGALL) was used for the fully automatic classification of EEG-vigilance stages (indicating arousal states) of 1-second EEG segments; VIGALL-derived measures of brain arousal were calculated. We found that depressed patients scored higher on arousal stability (Z = −2.163, P = .015) and A stages (dominant alpha activity; P = .027) but lower on B1 stages (low-voltage non-alpha activity, P = .008) compared with healthy controls. No significant group differences were observed in Stage B2/3. In summary, we were able to demonstrate stable and elevated brain arousal during brief 2-minute recordings at rest in depressed patients. Results set the stage for examining the value of these measures for predicting clinical response to antidepressants in the entire EMBARC sample and evaluating whether an upregulated brain arousal is particularly characteristic for responders to antidepressants

Aerosol properties and meteorological conditions in the city of Buenos Aires, Argentina, during the resuspension of volcanic ash from the Puyehue-Cordón Caulle eruption

The eruption in June 2011 of the Puyehue-Cordón Caulle Volcanic Complex in Chile impacted air traffic around the Southern Hemisphere for several months after the initial ash emissions. The ash deposited in vast areas of the Patagonian Steppe was subjected to the strong wind conditions prevalent during the austral winter and spring experiencing resuspension over various regions of Argentina. <br><br> In this study we analyze the meteorological conditions that led to the episode of volcanic ash resuspension which impacted the city of Buenos Aires and resulted in the closure of the two main airports in Buenos Aires area (Ezeiza and Aeroparque) on 16 October 2011. A relevant result is that resuspended material (volcanic ash plus dust) imprints a distinguishable feature within the atmospheric thermodynamic vertical profiles. The thermodynamic soundings show the signature of "pulses of drying" in layers associated with the presence of hygroscopic ash in the atmosphere that has already been reported in similar episodes after volcanic eruptions in other parts of the world. This particular footprint can be used to detect the probable existence of volcanic ash layers. This study also illustrates the utility of ceilometers to detect not only cloud base at airports but also volcanic ash plumes at the boundary layer and up to 7 km altitude. <br><br> Aerosol properties measured in the city during the resuspension episode indicate the presence of enhanced concentrations of aerosol particles in the boundary layer along with spectral signatures in the measurements at the Buenos Aires AERONET site typical of ash plus dust advected towards the city. The mandatory aviation reports from the National Weather Service about airborne and deposited volcanic ash at the airport near the measurement site (Aeroparque) correlate in time with the enhanced concentrations. The presence of the resuspended material was detected by the CALIOP lidar overpassing the region. Since the dynamics of ash resuspension and recirculation are similar to the dynamics of dust storms, we use the HYSPLIT model with the dust storm module to simulate the episode that affected Buenos Aires. The results of the modeling agree qualitatively with satellite lidar measurements