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Sorribas M.,Atmospheric Research and Instrumentation Branch | Sorribas M.,University of Granada | De La Morena B.A.,Atmospheric Research and Instrumentation Branch | Wehner B.,Leibniz Institute for Tropospheric Research | And 6 more authors.
Atmospheric Chemistry and Physics | Year: 2011

This study focuses on the analysis of the sub-micron aerosol characteristics at El Arenosillo Station, a rural and coastal environment in South-western Spain between 1 August 2004 and 31 July 2006 (594 days). The mean total concentration (NT) was 8660 cm-3 and the mean concentrations in the nucleation (NNUC), Aitken (NAIT) and accumulation (NACC) particle size ranges were 2830 cm-3, 4110 cm-3 and 1720 cm-3, respectively. Median size distribution was characterised by a single-modal fit, with a geometric diameter, median number concentration and geometric standard deviation of 60 nm, 5390 cm-3 and 2.31, respectively. Characterisation of primary emissions, secondary particle formation, changes to meteorology and long-term transport has been necessary to understand the seasonal and annual variability of the total and modal particle concentration. Number concentrations exhibited a diurnal pattern with maximum concentrations around noon. This was governed by the concentrations of the nucleation and Aitken modes during the warm seasons and only by the nucleation mode during the cold seasons. Similar monthly mean total concentrations were observed throughout the year due to a clear inverse variation between the monthly mean NNUC and NACC. It was related to the impact of desert dust and continental air masses on the monthly mean particle levels. These air masses were associated with high values of NACCwhich suppressed the new particle formation (decreasing N NUC). Each day was classified according to a land breeze flow or a synoptic pattern influence. The median size distribution for desert dust and continental aerosol was dominated by the Aitken and accumulation modes, and marine air masses were dominated by the nucleation and Aitken modes. Particles moved offshore due to the land breeze and had an impact on the particle burden at noon, especially when the wind was blowing from the NW sector in the morning during summer time. This increased NNUC and NAIT by factors of 3.1 and 2.4, respectively. Nucleation events with the typical "banana" shape were characterised by a mean particle nucleation rate of 0.74 cm-3 s-1, a mean growth rate of 1.96 nm h -1and a mean total duration of 9.25 h (starting at 10:55 GMT and ending at 20:10 GMT). They were observed for 48 days. Other nucleation events were identified as those produced by the emissions from the industrial areas located at a distance of 35 km. They were observed for 42 days. Both nucleation events were strongly linked to the marine air mass origin. © 2011 Author(s). Source

Cuevas E.,Izana Atmospheric Research Center | Camino C.,Izana Atmospheric Research Center | Benedetti A.,ECMWF | Basart S.,Barcelona Supercomputing Center | And 11 more authors.
Atmospheric Chemistry and Physics | Year: 2015

In the present work, atmospheric mineral dust from a MACC-II short reanalysis run for 2 years (2007-2008) has been evaluated over northern Africa and the Middle East using satellite aerosol products (from MISR, MODIS and OMI satellite sensors), ground-based AERONET data, in situ PM10 concentrations from AMMA, and extinction vertical profiles from two ground-based lidars and CALIOP satellite-based lidar. The MACC-II aerosol optical depth (AOD) spatial and temporal (seasonal and interannual) variability shows good agreement with those provided by satellite sensors. The capability of the model to reproduce the AOD, Ångström exponent (AE) and dust optical depth (DOD) from daily to seasonal time-scale is quantified over 26 AERONET stations located in eight geographically distinct regions by using statistical parameters. Overall DOD seasonal variation is fairly well simulated by MACC-II in all regions, although the correlation is significantly higher in dust transport regions than in dust source regions. The ability of MACC-II in reproducing dust vertical profiles has been assessed by comparing seasonal averaged extinction vertical profiles simulated by MACC-II under dust conditions with corresponding extinction profiles obtained with lidar instruments at M'Bour and Santa Cruz de Tenerife, and with CALIOP. We find a good agreement in dust layers structures and averaged extinction vertical profiles between MACC-II, the lidars and CALIOP above the marine boundary layer from 1 to 6 km. Surface dust daily mean concentrations from MACC-II reanalysis has been evaluated with daily averaged PM10 at three monitoring stations of the Sahelian Dust Transect. MACC-II correctly reproduces daily to interannual surface dust concentration variability, although it underestimates daily and monthly means all year long, especially in winter and early spring (dry season). MACC-II reproduces well the dust variability recorded along the station transect which reflects the variability in dust emission by different Saharan sources, but fails in reproducing the sporadic and very strong dust events associated to mesoscale convective systems during the wet season. © Author(s) 2015. Source

Sorribas M.,University of Granada | Ogren J.A.,National Oceanic and Atmospheric Administration | Olmo F.J.,University of Granada | Quirantes A.,University of Granada | And 3 more authors.
Tellus, Series B: Chemical and Physical Meteorology | Year: 2015

Desert dust (DD) aerosols reach the El Arenosillo observatory (southwest Spain) following two characteristic pathways at sea level, each showing significant differences in its aerosol microphysical and optical properties. These differences, in turn, determine the influence on the radiative forcing over the region. For these events, the meteorological scenarios show a depression located over North Africa at ground level. A Mediterranean pathway occurs when: (1) the depression is located over North Africa and the Mediterranean Basin or (2) it is coupled to a high pressure in higher latitudes. A North Africa pathway is observed when the depression is located only over North Africa. In our inventory, there are clear DD episodes under the Mediterranean flow, whereas other specific DD events take place under a mixture of Mediterranean and North African flows. The pure Mediterranean flow is associated with a higher increase of particle volume and scattering coefficient within the sub-micron than the super-micron size ranges. This result indicates that the contribution to the radiative forcing through the scattering processes over the region for particles with D<1 mm is larger than for particles with D>1 mm. In contrast, the episodes with a mixture of Mediterranean and North African flows show a similar effect of sub- and super-micron size ranges on radiative forcing. The size range with the largest impact on the scattering processes is 0.3 μm < D < 0.6 μm. Similar temporal variability of in situ and columnar-integrated aerosol properties on episodes with mixed flow suggests that the amounts of aerosols within the super-micron size range at the surface and aloft are correlated. During the episodes with pure Mediterranean flow, the amounts of aerosol vary independently within all size ranges, but the particle size distributions at surface and aloft are similar. © 2015 M. Sorribas et al. Source

Sorribas M.,University of Granada | Olmo F.J.,University of Granada | Quirantes A.,University of Granada | Lyamani H.,University of Granada | And 3 more authors.
Quarterly Journal of the Royal Meteorological Society | Year: 2015

A study has been carried out to assess the discrepancies between computed and observed aerosol scattering and backscattering properties in the atmosphere. The goals were: (i) to analyse the uncertainty associated with computed optical properties when spherical and spheroidal approximations are used, and (ii) to estimate nephelometry errors due to angular truncation and non-Lambertian illumination of the light source in terms of size range, particle shape and aerosol chemical compounds. Mie and T-matrix theories were used for computing light optical properties for spherical and spheroidal particles, respectively, from observed particle size distributions. The scattering coefficient of the fine mode was not much influenced by the particle shape. However, computed backscattering values underestimated the observed values by ∼15%. For the coarse mode, the spheroidal approximation yielded better results than that for spherical particles, especially for backscattering properties. Even after applying the spheroidal approximation, computed scattering and backscattering values within the coarse mode underestimated the observed values by ∼49% and ∼11%, respectively. The angular correction most widely used to correct the nephelometer data was discussed to explore its uncertainty. In the case of the scattering properties within the coarse mode, the change of the computed optical parameter is ∼+8% and for the scattering and backscattering values within the fine mode it is lower than ∼±4% for spherical and spheroidal particles. Additionally, if the spheroidal particles are used to evaluate the aerosol optical properties, the correction must be reconsidered with the aim of reducing the uncertainty found for scattering within the coarse mode. This is recommended for sites with desert dust influence; then the deviation of the computed scattering can be up to 13%. © 2015 Royal Meteorological Society. Source

Lopez J.F.,University of Valladolid | Lopez J.F.,Atmospheric Research and Instrumentation Branch | Cachorro V.E.,University of Valladolid | Sorribas M.,Atmospheric Research and Instrumentation Branch | And 2 more authors.
Optica Pura y Aplicada | Year: 2011

Aerosol scattering properties have been measured over two years (January 2006 to May 2008) at the monitoring station ESAT-El Arenosillo as part of the development of the "Laboratorio de Medida de Aerosoles" in situ into the scientific collaboration between INTA National Institute of Aerospace Technique of Spain) and "Atmospheric Optics Group of the University of Valladolid (GOA-UVA). This station belonging to INTA is located in the coastal area of the province of Huelva (Southwestern of Spain). Light scattering coefficient σ sp and hemispheric back-scattering coefficient σ bsp were measured using a 3-wavelengths (450, 550 and 700 nm) integrating nephelometer of TSI Model 3563, under specified GAW dry conditions. Ångström exponent α has been also derived from the spectral scattering dependence and the hemispheric backscatter fraction b from the ratio σ bsp/σ sp. All these parameters have been carefully analyzed to investigate their general characteristics and features, as annual, seasonal and diurnal variability. © Sociedad Española de Óptica. Source

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