Profiling Sea Ice with a Multiple Altimeter Beam Experimental Lidar (MABEL)

The sole instrument on the upcoming ICESat-2 altimetry mission is a micropulse lidar that measures the time-of-flight of individual photons from laser pulses transmitted at 532 nm. Prior to launch, MABEL serves as an airborne implementation for testing and development. In this paper, we provide a first examination of MABEL data acquired on two flights over sea ice in April 2012: one north of the Arctic coast of Greenland, and the other in the East Greenland Sea.We investigate the phenomenology of photon distributions in the sea ice returns. An approach to locate the surface and estimate its elevation in the distributions is described, and its achievable precision assessed. Retrieved surface elevations over relatively flat leads in the ice cover suggest that precisions of several centimeters are attainable. Restricting the width of the elevation window used in the surface analysis can mitigate potential biases in the elevation estimates due to subsurface returns at 532 nm. Comparisons of nearly coincident elevation profiles from MABEL with those acquired by an analog lidar show good agreement.Discrimination of ice and open water, a crucial step in the determination of sea ice free board and the estimation of ice thickness, is facilitated by contrasts in the observed signal background photon statistics. Future flight lines will sample a broader range of seasonal ice conditions for further evaluation of the year-round profiling capabilities and limitations of the MABEL instrument

Updating the Treatment of the Direct Aerosol Effect in the Global Environmental Multiscale Model With Atmospheric Chemistry (GEM-AC)

Atmospheric aerosols alter the atmospheric energy budget through their scattering, absorption, and emission properties within certain spectral bands. The direct aerosol effect is a fundamental aspect of every climate and chemical transport model. Aerosol optical properties are incorporated into the Global Environmental Multiscale model with Atmospheric Chemistry (GEM-AC) which is equipped with the M7 aerosol submodel. With the recent progress in atmospheric and chemical transport modelling, an interactive dust emission scheme and a sea-state dependent sea salt emission scheme are also implemented in GEM-AC. An option between volume fraction mixing and Bruggeman mixing for the mixing state of soluble aerosols is provided. In addition, there is an option to include the aerosol direct effect at all nine longwave spectral bands in GEM-AC. Eight experiments are performed to document the new direct effect of the M7 aerosols and the effects of:the aerosols in all nine longwave spectral bands, the soluble aerosol mixing state options, the interactive dust scheme, and the sea-state dependent sea salt emission scheme. Aerosol optical properties are compared against three AERONET observation sites. Implementation of the aerosol direct effect and the new aerosol options in GEM-AC maintain the model as a practical tool for climate and chemical transport modelling

Understanding the measurements and variability of aerosol optical properties in NE Spain

[eng] Atmospheric aerosol particles are key for regulating Earth’s atmosphere processes, and are estimated to present an overall cooling effect on the Earth’s climate. Given the current climate change crisis, and the need for precise mitigation measures on anthropogenic emissions, it is paramount to reduce the uncertainties related to the actual degree of this cooling effect and the impact that the reduction on the aerosol particles emissions will have on the Earth’s radiative forcing and global temperature. The main sources of uncertainty of the contribution of aerosol particles to the radiative balance are associated to their highly variable and heterogeneous spatial and temporal distribution, to the large array of aerosol species with varying physico-chemical properties, and to the measurement associated errors. In particular, the most important aerosol species with regards to their absorption properties and effect on climate as warming agents are black carbon (BC), the organic aerosols (OA) absorbing fraction, referred to as brown carbon (BrC), and, potentially, mineral dust. The Mediterranean basin is a region in Southern Europe heavily affected by large anthropogenic emission sources, as well as from natural sources such as wildfires, Saharan dust mineral outbreaks and other biogenic processes. The multiple sources coupled with the meteorological conditions and the abrupt topography favour the accumulation and recirculation of air masses, especially during summer, which onsets the ageing of particles at several layers above ground, giving place to a complex mixture of aerosol particles. In this context, this PhD thesis main focus is on the characterization of the optical properties of the BC, BrC and mineral dust particles, and its variations under different meteorological scenarios over an area on the Western Mediterranean Basin (NE of Spain). More specifically, this thesis addresses improvements in i) the determination of the absorption coefficients from a highly deployed instrument, the dual-spot multi- wavelength AE33 aethalometer, via a novel approach; ii) the characterization of the horizontal and vertical distribution of the aerosol particles physico-chemical properties at a regional recirculation event and a Saharan dust event; and iii) the analysis of the effects on the absorption enhancement of the BC particles by its mixing with BrC and other non- absorbing organic and inorganic aerosols. Finally, this thesis describes the optical properties of mineral dust at an emission source in a Saharan arid region and introduces the variations related to the types of events and the strength of the emission processes. With this aim, this thesis combines datasets from monitoring stations at three different backgrounds and an intensive measurement campaign with instrumented flights in the NE of Spain, in addition to an intensive campaign in a mineral dust emission area in the Saharan outskirts. The monitoring stations in the NE of Spain are operated by the EGAR group (IDAEA-CSIC) at an urban background in Barcelona (BCN), a regional background in Montseny natural park (MSY), and a remote mountain-top station in Montsec d’Ares mountain range (MSA).[spa] Los aerosoles atmosféricos resultan claves a la hora de regular el clima de la Tierra, con un efecto sobre el clima estimado de enfriamiento a nivel global, si bien con una alta incertidumbre en su valor exacto. Es por ello necesario reducir dichas incertidumbres, principalmente asociadas a la alta variabilidad y heterogeneidad de su distribución espacial y temporal, las múltiples especies de aerosoles con diferentes propiedades físico-químicas, y los errores de medida. Las especies de aerosoles más relevantes debido a su efecto en el calentamiento del clima son el carbono negro (BC), la fracción absorbente de los aerosoles orgánicos (OA), i.e. carbono marrón (BrC), y, potencialmente, el polvo mineral. Para el estudio de las propiedades ópticas de los aerosoles, esta tesis se ha centrado en un área con una gran variabilidad de fuentes de emisión de aerosoles de origen natural (biogénicos, incendios, polvo mineral, sal marina) y antropogénico (tráfico, industria, viviendas, portuario, etc.) en el Mediterráneo, en el NE de España. Esta área presenta una orografía compleja que en combinación con patrones atmosféricos que promueven los sistemas de brisas favorece la recirculación de los aerosoles, generando múltiples capas de aerosoles. Además, dichos escenarios pueden verse también influidos por la presencia de advección de polvo mineral desde el N de África, contribuyendo significativamente a la concentración de material particulado y afectando las propiedades ópticas. Con el fin de mejorar la caracterización de las propiedades ópticas del BC, el BrC y el polvo mineral en el NE de España, esta tesis ha llevado a cabo una serie de estudios centrada en: i) la mejora de la medida de la absorción analizando a través de un método novedoso el comportamiento de un parámetro clave para su obtención mediante el aethalometro AE33, ii) la descripción de la variación vertical de las propiedades físico- químicas de los aerosoles atmosféricos durante eventos de recirculación e intrusiones de polvo mineral el verano de 2015 a través de la combinación de vuelos instrumentados y medidas en las estaciones de medida, iii) el efecto de la mezcla de OA y aerosoles inorgánicos con partículas de BC en su absorción, y iv) las propiedades ópticas del polvo mineral en una fuente de emisión en el Sahara según la intensidad de emisión

Deterioration of air quality across Sweden due to transboundary agricultural burning emissions

Targino, A. C., Krecl, P., Johansson, C., Swietlicki, E., Massling, A., Coraiola, G. C. & Lihavainen, H. 2013: Deterioration of air quality across Sweden due to transboundary agricultural burning emissions. Boreal Env. Res. 18: 19-36. We analyzed measurements of aerosol and trace-gas concentrations from sites across Sweden before and during a series of agricultural wildland fires in eastern Europe in spring 2006. During the burning episodes, concentrations of background particulate matter (PM) and trace gases, such as carbon monoxide and ozone, increased, affecting air quality across the country and violating national air quality standards. The European Union PM10 daily limit value of 50 mu g m(-3) was exceeded during the pollution episodes even at the background stations, resulting in a nearly four-fold increase as compared with that in non-episode conditions. In relation to a non-episode period, the concentration rise in the accumulation-mode particles was from 40% at an urban site to 340% at a rural site, causing an increase in total particle number concentrations. The fires also boosted ground-level ozone, increasing concentrations of this pollutant by up to 100% at the background stations, which exceeded national air quality standards. Both elemental (EC) and organic carbon (OC) levels increased, with OC making a larger contribution to the total carbonaceous concentrations during the biomass burning episodes. The large-scale atmospheric circulation determined the strength and timing of the pollution events, with the eastern and northern sectors of Sweden experiencing two pollution pulses, whilst sites in the western and southern sectors were affected by one shorter episode. The results show that regional air quality deteriorated due to the long-range transport of pollutants emitted during agricultural wildfires