A long Saharan dust event affected the western Mediterranean in the period 12–28 June 2002. Dust was present mainly between 1‐ and 5‐km height affecting most parts of the Iberian Peninsula and reaching western/central Europe. Intensive backscatter lidar observations over Barcelona (Spain) and Sun photometer data from two stations (El Arenosillo, Spain, and Avignon, France) are used to evaluate different configurations the Dust Regional Atmospheric Modeling (DREAM) system. DREAM currently operates dust forecasts over the Mediterranean region (http://www.bsc.es/projects/earthscience/DREAM/) considering four particle size bins while only the first two are relevant for long‐range transport analysis since their life time is larger than 12 hours. A more detailed bin method is implemented, and two different dust distributions at sources are compared to the operational version. Evaluations are performed at two wavelengths (532 and 1064 nm). The dust horizontal and vertical structure simulated by DREAM shows very good qualitative agreement when compared to SeaWIFS satellite images and lidar height‐time displays over Barcelona. When evaluating the modeled aerosol optical depth (AOD) against Sun photometer data, significant improvements are achieved with the use of the new detailed bin method. In general, the model underpredicts the AOD for increasing Ångström exponents because of the influence of anthropogenic pollution in the boundary layer. In fact, the modeled AOD is highly anticorrelated with the observed Ångström exponents. Avignon shows higher influence of small anthropogenic aerosols which explains the better results of the model at the wavelength of 1064 nm over this location. The uncertainties of backscatter lidar inversions (20–30%) are in the same order of magnitude as the differences between the model experiments. Better model results are obtained when comparing to lidar because most of the anthropogenic effect is removed.

Routine aerosol measurements have been carried out at INTA–El Arenosillo (Huelva, Spain) since February 2000 with a Cimel sun photometer integrated in the global aerosol monitoring network AERONET. A 5‐year aerosol database allows characterization and classification of aerosol properties, which define the local aerosol climatology. In this work two basic parameters for aerosol characterization, aerosol optical depth (AOD) and Ångström exponent, α, are used for aerosol analysis. The mean AOD is 0.18 ( ± 0.14) and the mean α is 1.05 ( ± 0.43). The AOD presents two peaks during the year, at the end of the winter and during the summer, which are related to the seasonal patterns of the desert dust aerosols which arrive at the south‐western Iberian Peninsula from North Africa. The Ångström exponent presents two frequency modes, related to the two main aerosol types present at El Arenosillo: coastal marine aerosols and desert dust. A main aerosol scenario (66% of data) is defined as coastal marine aerosols, with the influence of local sources of continental and polluted aerosols. Continental aerosols are present in 11% of cases, while the desert dust has a very relevant occurrence in around 20% of the data. Copyright © 2007 Royal Meteorological Society

Large sets of filtered actinometer, filtered pyrheliometer and Sun photometer measurements have been carried out over the past 30 years by various groups at different Arctic and Antarctic sites and for different time periods. They were examined to estimate ensemble average, long‐term trends of the summer background aerosol optical depth AOD(500 nm) in the polar regions (omitting the data influenced by Arctic haze and volcanic eruptions). The trend for the Arctic was estimated to be between −1.6% and −2.0% per year over 30 years, depending on location. No significant trend was observed for Antarctica. The time patterns of AOD(500 nm) and Ångström's parameters α and β measured with Sun photometers during the last 20 years at various Arctic and Antarctic sites are also presented. They give a measure of the large variations of these parameters due to El Chichon, Pinatubo, and Cerro Hudson volcanic particles, Arctic haze episodes most frequent in winter and spring, and the transport of Asian dust and boreal smokes to the Arctic region. Evidence is also shown of marked differences between the aerosol optical parameters measured at coastal and high‐altitude sites in Antarctica. In situ optical and chemical composition parameters of aerosol particles measured at Arctic and Antarctic sites are also examined to achieve more complete information on the multimodal size distribution shape parameters and their radiative properties. A characterization of aerosol radiative parameters is also defined by plotting the daily mean values of α as a function of AOD(500 nm), separately for the two polar regions, allowing the identification of different clusters related to fifteen aerosol classes, for which the spectral values of complex refractive index and single scattering albedo were evaluated.

The Aerosol Robotic Network (AERONET) site “El Arenosillo,” equipped with a Cimel sun photometer, has been in operation since 2000. The data collected there are analyzed to establish an aerosol synoptic climatological description that is representative of the region. Different air masses and aerosol types are present over the site depending on the synoptic conditions. The frequent intrusion of dust from the Sahara Desert at El Arenosillo suggested the use of back trajectories to determine the airmass origins of other types of aerosol observed there. The focus of this study is to classify the air masses arriving at El Arenosillo by means of back-trajectory analyses and to characterize the aerosol within each type by means of the aerosol optical depth (AOD) and its spectral signature, given as the Ångström exponent (AE). The goal is to determine how aerosols observed over the station (receptor site) differ depending on source region and transport pathways. Two classification methods are used, one based on sectors and a second based on cluster analysis. The period analyzed is from 2000 to 2004. Both methods show that maritime air masses are predominant, occurring 70% of the time and having relatively low AOD (≈0.1 at 440 nm) and a wide range of AE (from about 0 to 2.0). Air masses with continental characteristics are moderately turbid and have values of AE that average ≈1.4. Air masses arriving from the south and southwest show the distinct features of the desert dust, having moderate to high values of AOD (0.30–0.35 at 440 nm) and low values of AE.

We present the analysis of the strongest North African desert dust (DD) intrusion that occurred over the Iberian Peninsula (IP) during the last decade, as registered by modern remote sensing techniques like Sun photometry. This event took place from 22 July to 3 August 2004. The most relevant features of this exceptional event, originated over the Saharan desert, were its great intensity and duration. We focus on the columnar aerosol properties measured by the AERONET‐Cimel photometers at El Arenosillo (southwest) and Palencia (north‐center) stations. Aerosol optical depth (AOD) reached a maximum of 2.7 at El Arenosillo during 22 July and 1.3 at Palencia on 23 July, with the Ånsgtröm exponent values near zero during the AOD peaks. In addition, PM10 concentration levels are also reported at various sites of the IP in order to establish the impact of this intrusion, reaching daily values as high as 200 μg/m³ and peaks near 600 μg/m³ in an hourly basis. The interest of this special event is increased because of the mixing with smoke particles from concurrent forest fires in the IP. Features of the columnar volume particle size distribution and derived microphysical parameters, the single scattering albedo, and a reliable estimation of the radiative forcing under these extreme conditions are also reported. Complementary information, as air mass back trajectories, synoptic charts, images, and AOD maps of satellite sensors (SeaWIFS, MODIS) together with NAAPS prognostic model, is used in the analysis in order to draw a detailed scenario of this dust‐smoke event over the IP.