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- The strongest desert dust intrusion mixed with smoke over the Iberian Peninsula registered with Sun photometryPublication . Cachorro, Victoria; Toledano, C.; Prats, N.; Sorribas, Mar; Mogo, Sandra; Berjón, Alberto Jesús; Torres, B.; Rodrigo, R.; de la Rosa, Jesús D; De Frutos, Ángel MWe 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 mg/m3 and peaks near 600 mg/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.
- Detailed Aerosol Optical Depth Intercomparison between Brewer and Li-Cor 1800 Spectroradiometers and a Cimel Sun PhotometerPublication . Cachorro, Victoria; Berjón, Alberto Jesús; Toledano, Carlos; Mogo, Sandra; Prats, Natalia; de Frutos, Ángel M; Vilaplana, Jose Manuel; Sorribas, Mar; De La Morena, Benito Arturo; Gröbner, J.; Laulainen, Nels S.Aerosol optical depth (AOD) using different instruments during three short and intensive campaigns carried out from 1999 to 2001 at El Arenosillo in Huelva, Spain, are presented and compared. The specific aim of this study is to determine the level of agreement between three different instruments running in operational conditions. This activity, however, is part of a broader objective to recover an extended data series of AOD in the UV range obtained from a Brewer spectroradiometer. This instrument may be used to obtain AOD at the same five UV wavelengths used during normal operation for ozone content determination. As part of the validation of the Brewer AOD data, a Cimel sun photometer and another spectroradiometer, a Li-Cor 1800, were used. A detailed comparison of these three instruments is carried out by means of near-simultaneous measurements, with particular emphasis on examining diurnal AOD variability. Absolute AOD uncertainties range from 0.02 for the Cimel to 0.08 for the Brewer, with intermediate values for the Li-Cor 1800. All data during the comparison are in reasonable agreement, when taking into account the different performance characteristics of each instrument. The comparison also demonstrates current deficiencies in the Brewer data and thus the difficulty to determine AOD values with low errors.
- Columnar aerosol optical properties during “El Arenosillo 2004 summer campaign”Publication . Prats, Natalia; Cachorro, Victoria; Sorribas, M.; Mogo, Sandra; Berjón, Alberto Jesús; Toledano, Carlos; De Frutos, Ángel M; de la Rosa, Jesús D; Laulainen, Nels S.; de la Morena, Benito ArturoA detailed analysis of the columnar optical aerosol properties has been carried out for data collected during the ‘‘El Arenosillo 2004 summer campaign’’. These data are derived from a Cimel sun-photometer, as part of the PHOTONS-AERONET network at the El Arenosillo site in south-western Spain, over the period 1 June to 31 October 2004. Version 1 AERONET inversion products are used in the analysis. The aim of this campaign was to obtain a more complete set of data on aerosol particle microphysical, optical/radiative, absorbing and chemical properties for use in closure studies. In his paper we focus on the characterization of the aerosol optical depth (AOD)–alpha coefficients, and the particle size distribution together with their associated microphysical parameters, such as volume concentration, effective radius, etc., in order to define the features and ranges of these physical parameters associated with both fine and coarse particle modes. The requirement of high AOD values for using the inversion technique puts significant constraints on the estimation of the single scattering albedo (SSA) and refractive index, and thus requires great care in the analysis. As a result, only the characterizations of these parameters for desert dust events are considered reliable. Moreover, summer 2004 had the most frequent desert dust intrusions, including the most intense event (22–28 July and 31 July–2 August) ever recorded at the El Arenosillo site since the start of the measurements in February 2000. We summarize the results for the intensive summer campaign in terms of the range of values of the physical and optical parameters of the different aerosol types present in this area of Spain.
- Comparing surface measurement of black carbon and columnar AERONET inferred contents during the “El Arenosillo 2004 summer campaignPublication . Mogo, Sandra; Cachorro, Victoria; De Frutos, Ángel M; De La Rosa, Jesús D; Sorribas, MarDuring the summer of 2004 a field campaign was carried out at the El Arenosillo Atmospheric Sounding Station (ESAt), near Huelva, South-Western Spain. The campaign was designed to obtain experimental data on aerosol in situ absorption, size distribution, chemical composition, and columnar optical properties but this paper deals only with the evaluation of the absorbent aerosol. A Dekati cascade impactor and a PM10 Graseby-Andersen high volume sampler were used to collect aerosol fractions over filters. In this paper an estimation is made for the concentration of black carbon at ground level, using the absorption coefficients obtained from a filter transmission method. The values obtained are highly variable and range from 31 ng m-3 to 770 ng m-3. The high volume sampler filters were analyzed for elemental carbon with a thermal- optical method (LECO). The black carbon concentration is also compared with the columnar level retrieved from aerosol absorption optical depth derived from inversion of a sun-photometer data inside the AERONET framework.
- Measurements of continuous spectra of atmospheric absorption coefficients from UV to NIR via optical methodPublication . Mogo, Sandra; Cachorro, Victoria; Sorribas, Mar; de Frutos, Ángel M; Fernández, R.In this study we extend from the visible to the UV a traditional method for studying the radiative properties of black carbon. We apply this measuring possibility to a practical study carried out in the Southern Iberian Peninsula during summer 2004. Using an optical technique based on the integrating sphere method, absorption coefficients, sa, were determined in the visible and in the ultraviolet regions of spectrum. The obtained values are representative of remote areas including during desert episodes that reach this area. To analyse the spectral shape of sa we derived a parameter (aa) which is the slope of the linear fit of the log- log plot of sa versus l. This parameter is similar to the Ångstrom exponent used for extinction. The reported aa values for the UV appear as very original data in the literature.
- Optical and chemical properties of atmospheric PM fractions related with air masses in the central Iberian PeninsulaPublication . Mogo, Sandra; Cachorro, Victoria; Sorribas, Mar; de Frutos, Ángel MFrom December 2003 to June 2004 approximately weekly aerosol samples were collected in Valladolid, Spain. Gravimetric measurements were performed on the four particulate matter fractions: TSP, PM10, PM2.5 and PM1. The samples were analyzed for major ions by ion-chromatography. The optical properties of the fine particles are studied through the absorption coefficients, σa, in the visible range and the spectral shape of σa was analyzed by deriving a parameter, αa, similar to the Ångström exponent used for the extinction. Aerosol properties are classified according to their dependence on air mass origin.
- On the sub-micron aerosol size distribution in a coastal-rural site at El Arenosillo Station (SW – Spain)Publication . Sorribas, Mar; De La Morena, B. A.; Wehner, B.; López, J. F.; Prats, N.; Mogo, Sandra; Wiedensohler, A.; Cachorro, VictoriaAbstract. This study focuses on the analysis of the submicron 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 NACC which suppressed the new particle formation (decreasing NNUC ). 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 off-shore 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−1 and 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.