Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 2 de 2
Mais filtros

Base de dados
Intervalo de ano de publicação
Chemosphere ; 197: 306-317, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29353680


The Antarctic Plateau snowpack is an important environment for the mercury geochemical cycle. We have extensively characterized and compared the changes in surface snow and atmospheric mercury concentrations that occur at Dome C. Three summer sampling campaigns were conducted between 2013 and 2016. The three campaigns had different meteorological conditions that significantly affected mercury deposition processes and its abundance in surface snow. In the absence of snow deposition events, the surface mercury concentration remained stable with narrow oscillations, while an increase in precipitation results in a higher mercury variability. The Hg concentrations detected confirm that snowfall can act as a mercury atmospheric scavenger. A high temporal resolution sampling experiment showed that surface concentration changes are connected with the diurnal solar radiation cycle. Mercury in surface snow is highly dynamic and it could decrease by up to 90% within 4/6 h. A negative relationship between surface snow mercury and atmospheric concentrations has been detected suggesting a mutual dynamic exchange between these two environments. Mercury concentrations were also compared with the Br concentrations in surface and deeper snow, results suggest that Br could have an active role in Hg deposition, particularly when air masses are from coastal areas. This research presents new information on the presence of Hg in surface and deeper snow layers, improving our understanding of atmospheric Hg deposition to the snow surface and the possible role of re-emission on the atmospheric Hg concentration.

Poluentes Atmosféricos/análise , Atmosfera/química , Mercúrio/análise , Neve/química , Regiões Antárticas , Monitoramento Ambiental , Águas Salinas/química , Estações do Ano
Appl Opt ; 44(16): 3302-11, 2005 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-15943267


A new algorithm to infer structural parameters such as refractive index and asphericity of cloud particles has been developed by use of in situ observations taken by a laser backscattersonde and an optical particle counter during balloon stratospheric flights. All three main particles, liquid, ice, and a no-ice solid (NAT, nitric acid trihydrate) of polar stratospheric clouds, were observed during two winter flights performed from Kiruna, Sweden. The technique is based on use of the T-matrix code developed for aspherical particles to calculate the backscattering coefficient and particle depolarizing properties on the basis of size distribution and concentration measurements. The results of the calculations are compared with observations to estimated refractive indices and particle asphericity. The method has also been used in cases when the liquid and solid phases coexist with comparable influence on the optical behavior of the cloud to estimate refractive indices. The main results prove that the index of refraction for NAT particles is in the range of 1.37-1.45 at 532 nm. Such particles would be slightly prolate spheroids. The calculated refractive indices for liquid and ice particles are 1.51-1.55 and 1.31-1.33, respectively. The results for solid particles confirm previous measurements taken in Antarctica during 1992 and obtained by a comparison of lidar and optical particle counter data.

Algoritmos , Atmosfera/análise , Monitoramento Ambiental/métodos , Lasers , Refratometria/métodos , Água/análise , Tempo (Meteorologia) , Clima Frio , Coloides/análise , Tamanho da Partícula , Espalhamento de Radiação