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- An integrating sphere spectral system to measure continuous spectra of aerosol absorption coefficientPublication . Montilla, E.; Mogo, Sandra; Cachorro, Victoria; De Frutos, Ángel MAn integrating sphere spectral system has been developed that allows the measurement of continuous spectra of light absorption coefficients, saðlÞ of atmospheric aerosols. This system is based on the filter attenuation method covering the spectral wavelength range 320–800 nm with a variable spectral resolution. The sample filters had to be diluted in chloroform previous to the light attenuation measurements and hence the system cannot measure continuously but only on the basis of daily sampling. The system was calibrated using known amounts of absorbing and non-absorbing industrial substances at relevant atmospheric absorption levels. The resulting values of sa ðlÞ were compared with those delivered by a commercial photometer (particle soot absorption photometer) in the laboratory and also with field measurements, with a maximum discrepancy of 12.5% for atmospherically relevant values. The measurement uncertainty of the integrating sphere system is about 10% maximum. The importance of obtaining continuous spectral data is the possibility to determine the Ångström absorption exponent, aa , in different spectral ranges, including the UV. This exponent can then be used to help in obtaining the aerosol composition information.
- 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.
- In situ UV-VIS-NIR absorbing properties of atmospheric aerosol particles: Estimates of the imaginary refractive index and comparison with columnar valuesPublication . Mogo, Sandra; Cachorro, Victoria; de Frutos, Ángel MIn this work, a novel technique is used to estimate the aerosol complex index of refraction of in situ collected samples. Samples of atmospheric particulate matter were collected in El Arenosillo, southern Spain, on polycarbonate filters during summer 2004 as part of an aerosol characterization campaign. These samples were analyzed for the volumetric absorption coefficient in the 320e800 nm spectral region and an estimation of the effective imaginary refractive index was made. The values of the imaginary part of the complex refractive index ranged between 0.0009e0.0215 at 800 nm and 0.0015e0.0114 at 320 nm. Little dependence on the wavelength was observed. Several intense and long lasting desert outbreaks were registered during the campaign and the complex refractive index almost doubles its value during these dust events. Finally, we present a comparison of data obtained in situ with columnar data obtained from the AERONET network. A correlation factor of 0.64 was obtained between both data, which gives an idea of how accurately the in situ ground data represent the total column.
- 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.
- Absorption Ångström exponents of aerosols and light absorbing carbon (LAC) obtained from in situ data in Covilhã, central PortugalPublication . Mogo, Sandra; Cachorro, Victoria; de Frutos, Ángel M; Rodrigues, A.A field campaign was conducted from October 2009 to July 2010 at Covilhã, a small town located in the region of Beira Interior (Portugal) in the interior of the Iberian Peninsula. The ambient light-absorption coefficient, σ(a) (522 nm), obtained from a Particle Soot Absorption Photometer (PSAP), presented a daily mean value of 12.1 Mm⁻¹ (StD = 7.3 Mm⁻¹). The wavelength dependence of aerosol light absorption is investigated through the Ångström parameter, α(a). The α(a) values for the pair of wavelengths 470-660 nm ranged from 0.86 to 1.47 during the period of measurements. The PSAP data were used to infer the mass of light absorbing carbon (LAC) and the daily mean varied from 0.1 to 6.8 μg m⁻³. A detailed study of special events with different aerosol characteristics is carried out and, to support data interpretation, air masses trajectory analysis is performed.
- Atmospheric particulate matter levels, chemical composition and optical absorbing properties in Camagüey, CubaPublication . Barja, Boris; Mogo, Sandra; Cachorro, Victoria; Antuña, Juan Carlos; Estevan, Rene; Rodrigues, Ana; de Frutos, Ángel MAtmospheric aerosol particles were collected at Camagüey, Cuba, during the period from February 2008 to April 2009 in order to know the particulate matter levels (PM) together with a general chemical and absorption characterization. The aerosols collection was carried out with a low volume particulate impactor twice a week. Gravimetric analysis of the particulate matter fractions PM10 and PM1 was carried out. An analysis of the eight major inorganic species (Na+, K +, Ca2+ , Mg2+, NH4+, Cl , NO3 and SO42 ) using ionic chromatography was conducted. The results were analyzed in two periods, the high aerosol concentration period (May to August) and the period with low aerosol concentration (the other months). During the high concentration period the average PM10 and PM1 levels were 35.11 mg m 3 (std 1⁄4 15.45 mg m 3) and 16.86 mg m 3 (std 1⁄4 6.14 mg m 3). During the low concentration period the average PM10 and PM1 levels were 23.13 mg m 3 (std 1⁄4 5.00 mg m 3) and 13.00 mg m 3 (std 1⁄4 4.02 mg m 3). For both periods, Cl , Na+ and NO3 are the predominant species in the coarse fraction (PM1-10), and SO42 and NH4+ are the predominant species in the fine fraction (PM1). The spectral aerosol absorption coefficient, sa, was measured for the wavelength range 400–700 nm with 10 nm steps. The sa values were obtained with a filter transmission method for the fine fraction and were evaluated for 54 days covering a wide range of atmospheric conditions including a Saharan dust intrusion. sa ranges from 8.5 M m 1 to 34.5 M m 1 at a wavelength of 550 nm, with a mean value of 18.7 M m 1. The absorption Ångström parameter, aa, calculated for the pair of wavelengths (450/700 nm) presents a mean value of 0.33 (std 1⁄4 0.19), which is a very low value comparing with those that can be found in the bibliography. Although the sampling period is short, these data represent the first evaluation of PM values with their chemical and optical absorption characterization in Cuba. In addition to the regional interest, the presented values can be directly used by those working with absorption, forcing by aerosols and radiative transfer calculations in general. Also, these data can be used as input in Global Climate Models.
- Atmospheric particulate matter fractions measured at Camagüey, Cuba. Preliminary resultsPublication . Barja, Boris; Antuña, Juan Carlos; Estevan, Rene; Mogo, Sandra; Montilla, Elena; Cachorro, Victoria; De Frutos, Ángel MGravimetric measurements of the particulate matter fractions PM10 and PM1, conducted at Camagüey, Cuba are reported. Samples were collected with a low volume particulate impactor Dekati PM10 two times a week, between February and October 2008. Sampling was conducted both under the local background conditions and in the presence of the Saharan dust events. The mean values of particulate matter concentrations were 28.4 μg/m3 and 14.6 μg/m3 for PM10 and PM1, respectively. The maximum/minimum concentrations of particulate matter measured for PM10 and PM1 were 73.3 μg/m3 / 13.1 μg/m3 and 33.4 μg/m3 / 4.9 μg/m3, respectively. An analysis of the eight major inorganic species (Na+, K+, Ca2+, Mg2+, NH4+, Cl–, NO3– and SO4 2–) in aerosol samples using ionic chromatography was conducted. An aerosol classification was developed depending on the air masses origins, wind velocity and direction at the measured site. The air masses origins were determined using backward trajectories derived from the HYSPLIT model.
- Morphological, chemical and optical absorbing characterization of aerosols in the urban atmosphere of ValladolidPublication . Mogo, Sandra; Cachorro, Victoria; de Frutos, Ángel MSamples of atmospheric aerosol particles were collected in Valladolid, Spain, during the winter of 2003–2004. The measurements were made with a Dekati PM10 cascade impactor with four size stages: greater than 10 μm, between 2.5 to 10 μm, 1 to 2.5 μm and less than 1 μm. The size and shape of the particles were analyzed with a scanning electron microscope (SEM) and elemental analysis was done with an energy dispersive x-ray analysis (EDX). We present an evaluation by size, shape and composition of the major particulate species in the Valladolid urban atmosphere. The total aerosol concentration is very variable, ranging from 39.86 μg·m−3 to 184.88 μg·m−3 with the coarse particles as the dominant mass fraction. Emphasis was given to fine particles (<1 μm), for which the visible (400 nm to 650 nm) light absorption coefficients were measured using the integrating plate technique. We have made some enhancements in the illumination system of this measurement system. The absorption coefficient, σa , is highly variable and ranges from 7.33×10−6 m−1 to 1.01×10−4 m−1 at a wavelength of 550 nm. There is an inverse power law relationship between σa and wavelength, with an average exponent of −0.8.
- 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.