222Rn as a tracer for air mass transport characterization at 100-m-high tower in the south-west Spanish coast

Abstract

Es los últimos años se han llevado a cabo importantes trabajos de investigación, tomando el gas radón como elemento de evaluación en modelos de transporte atmosférico y así estimar el flujo de partículas. Además la utilización del radón ha encontrado otras aplicaciones en el estudio de las emisiones de gases de efecto invernadero a escala regional; en la actualidad en algunos proyectos europeos como el Ttorch y el InGOS se realizan medidas en continuo de radón atmosférico junto con otros gases de efecto invernadero. En este marco de actuación, la presente tesis quiere caracterizar una nueva estación de radón atmosférico en El Arenosillo, en la cuenca sur de España, llevando a cabo medidas de radón a diferentes alturas gracias a una torre de 100 metros. Además otro objetivo de la tesis ha sido la caracterización del flujo de radón en esta área geográfica. Este trabajo incluye, además de un análisis de las concentraciones de radón mediante un sistema de esfera por electrodeposición, las observaciones de los parámetros meteorológicos en la estación de El Arenosillo. El flujo de radón en la misma área ha sido estudiado tanto con métodos directos como indirectos. Para poder estudiar el origen de las masas de aire ricas o pobres en radón que llegan a la estación, se ha realizado un análisis cualitativo con retro trayectorias.

An intensive research has been carried out during the last decade on a global scale using 222Rn for global atmospheric transport models evaluation as well as for estimating fluxes of atmospheric constituents. Furthermore, a new application in recent years has been the use of radon for estimating regional scale greenhouse gas emission. Nowadays, some European projects and data base, such as the TTtorch and the InGOS, are carrying out continuous measurements of the atmospheric 222Rn gas concentrations together with others greenhouse gases measurements at tall towers. In this framework, the present thesis aims to characterize a new atmospheric radon station at the El Arenosillo station, in the Southwest coast of Spain, by performing atmospheric radon concentration measurements at different heights thank to the presence of a 100 m tall tower. Furthermore, the study wants to properly characterize the radon flux background in this area. Therefore, this work includes the analysis of atmospheric radon gas concentration by electrostatic chamber method under seasonal meteorological parameters at two heights and the characterization of the radon flux of the El Arenosillo station area by direct and by indirect radon flux inventories. Finally, a qualitative back trajectories analysis has been performed to study the origin of air masses rich or poor in radon and to confirm the specific regions as radon source regions. During the Autumn season the geometric mean of radon data at 10 m is 4.48 Bq m-3 with a st. dev. of 2.03 Bq m-3 .and at 100 m is 2.93 with 1.98 Bq m-3 . In the Winter season the geometric mean of radon concentration data at 10 m is 3.82 Bq m-3 with a st. dev. of 2.34. At 100 m the geometric mean is and 3.06 Bq m-3 with 1.72. These radon concentrations are not as high as would be expected for winter and can be explained by the high frequency of radon-poor air masses coming from the Atlantic Ocean and from South Portugal during this season. The Spring season shows a geometric mean of radon concentration data at 10 m of 3.60 Bq m-3 with a st. dev. equal to 2.18 and at 100 m is 2.05 Bq m-3 with 2.20. These average radon concentrations indicate good atmospheric layer separation during this season. Finally, during the summer season the radon concentration data at 10 m is 2.64 Bq m-3 with a st. dev. of 1.86. At 100 m height, the geometric mean is 2.41 Bq m-3 with standard deviation of 1.88. These values indicate good statistics for this season and a strong mixing layer, as was expected for an unstable summer. The local radon flux contribution at el Arenosillo station is really low, of 5.3 ± 1.8 Bq m-2 h-1 which means that the atmospheric radon concentrations data will not have any strong noisly radon background and can be used in order to estimate remote radon source. The 222Rn flux observed from the close phosphogypsum pile and confirmed by different monitors and methods shows an average value of 33.5 ± 5.6 Bq m-2 h-1 , which is really low if compared with material 226Ra activity concentration of 550 Bq kg-1. The experimental analysis of atmospheric radon behaviour at El Arenosillo station has pointed out the existence of specific regions poor/rich in radon where the air masses use to come from such as the Sierra Morena system, the Betic system, the North of Portugal, the Atlantic Ocean, the Marocco area and the Guadalquivir Valley. A back-trajectory analysis has been performed by the transport model HYSPLIT4 in order to confirm the air masses origin from specific sectors and to justify the poor/rich radon concentrations transported and measured at El Arenosillo station.