Search

Simultaneous PM2.5, PM10 and columnar (ground and satellite based) AOD measurements have been analyzed at Burjassot site in the metropolitan area of Valencia (Spain) during the period 2007–2016. The site is representative of a south European city in the Western Mediterranean coastal area, influenced by local urban pollution but also from frequent Saharan dust events. First, multiannual statistics were performed to characterize the main aerosol burden characteristics. The averages and standard deviations resulted 18 ± 9 μg m−3, 25 ± 19 μg m−3, 0.15 ± 0.11, 0.23 ± 0.17, 0.19 ± 0.15 and 1.2 ± 0.3 for PM2.5, PM10, AERONET AOD, MODIS Terra AOD, MODIS Aqua AOD, and AERONET Angstrom exponent AE, respectively. The AOD is always referred to 550 nm. PM10 and AOD showed seasonal patterns with maxima in summer and minima in winter. However, PM2.5 and AE did not show such an evident seasonality. The relationship between surface and columnar measurements show a poor correlation (r down to 0.30) for daily values, although the correlation increases to r up to 0.90 for yearly averages. The relationship between PM and AOD becomes more consistent when the databases are binned in intervals of 0.05 AOD. Results for AERONET and MODIS AOD are very similar, although for daily averages is slightly worse for satellite than ground based measurements. In order to explain some seasonality effects found, the mixing layer height has been included in the analysis. Results show that the correlation is maximum when PM2.5 is used and the mixing layer height is greater than 1 000 m (r > 0.90).

SKYNET and Aerosol Robotic Network (AERONET) retrieved aerosol single scattering albedo (SSA) values of four sites, Chiba (Japan), Pune (India), Valencia (Spain), and Seoul (Korea), were compared to understand the factors behind often noted large SSA differences between them. SKYNET and AERONET algorithms are found to produce nearly same SSAs for similarity in input data, suggesting that SSA differences between them are primarily due to quality of input data due to different calibration and/or observation protocols as well as difference in quality assurance criteria. The most plausible reason for high SSAs in SKYNET is found to be underestimated calibration constant for sky radiance (ΔΩ). The disk scan method (scan area: 1° × 1° area of solar disk) of SKYNET is noted to produce stable wavelength-dependent ΔΩ values in comparison to those determined from the integrating sphere used by AERONET to calibrate sky radiance. Aerosol optical thickness (AOT) difference between them can be the next important factor for their SSA difference, if AOTs between them are not consistent. Inconsistent values of surface albedo while analyzing data of SKYNET and AERONET can also bring SSA difference between them, but the effect of surface albedo is secondary. The aerosol nonsphericity effect is found to be less important for SSA difference between these two networks.

Aerosol optical properties were derived from ground-based sunphotometer observations between 2009-2013 at three urban sites of Shenyang, Anshan, Fushun in northeastern China. The annual means for extinction aerosol optical depths (EAOD) at 500 nm were 0.57±0.38, 0.52±0.35, and 0.41±0.31 at Shenyang, Anshan, Fushun, respectively. The corresponding annual means for the extinction Angstrom exponents (EAE) computed for the wavelengths of 440 and 870 nm were 0.86±0.32, 0.86±0.34 and 0.91±0.35, respectively, indicating that urban area of Northeast China were affected by both coarse and fine particles. Hygroscopic growth in summer and incursions of dust aerosols in spring were evidently revealed from the analysis of the relationship between EAE and δ EAE (the EAE difference, δ EAE=EAE(440,670)−EAE(670,870)). The annual mean absorption aerosol optical depths (AAOD 440 nm ) values at Shenyang, Anshan, Fushun were 0.15±0.11, 0.10±0.07, 0.08±0.04, respectively. The annual mean absorption Angstrom exponents (AAE 440–870 nm ) values were 0.86±0.24, 1.19±0.39, 1.33±0.36 at Shenyang, Anshan, Fushun, respectively. When the AAEs were close to unity at Anshan, the absorption aerosol particles evidently consisted of black carbon from coal combustion and motor vehicles. Larger AAEs at Fushun were indicative of absorbing aerosols mainly from biomass burning and mineral dust. The AAE at Shenyang was

The estimation of the precipitable water vapour content (W) with high temporal and spatial resolution is of great interest to both meteorological and climatological studies. Several methodologies based on remote sensing techniques have been recently developed in order to obtain accurate and frequent measurements of this atmospheric parameter. Among them, the relative low cost and easy deployment of sun–sky radiometers, or sun photometers, operating in several international networks, allowed the development of automatic estimations of W from these instruments with high temporal resolution. However, the great problem of this methodology is the estimation of the sun-photometric calibration parameters. The objective of this paper is to validate a new methodology based on the hypothesis that the calibration parameters characterizing the atmospheric transmittance at 940 nm are dependent on vertical profiles of temperature, air pressure and moisture typical of each measurement site. To obtain the calibration parameters some simultaneously seasonal measurements of W, from independent sources, taken over a large range of solar zenith angle and covering a wide range of W, are needed. In this work yearly GNSS/GPS datasets were used for obtaining a table of photometric calibration constants and the methodology was applied and validated in three European ESR-SKYNET network sites, characterized by different atmospheric and climatic conditions: Rome, Valencia and Aosta. Results were validated against the GNSS/GPS and AErosol RObotic NETwork (AERONET) W estimations. In both the validations the agreement was very high, with a percentage RMSD of about 6, 13 and 8 % in the case of GPS intercomparison at Rome, Aosta and Valencia, respectively, and of 8 % in the case of AERONET comparison in Valencia. Analysing the results by W classes, the present methodology was found to clearly improve W estimation at low W content when compared against AERONET in terms of % bias, bringing the agreement with the GPS (considered the reference one) from a % bias of 5.76 to 0.52.

Variations in the optical properties of aerosols and their radiative forcing were investigated based on long-term synchronous observations made at three-minute intervals from 2011 to 2015 over seven adjacent CARSNET (China Aerosol Remote Sensing NETwork) urban (Hangzhou), suburban (Xiaoshan, Fuyang, LinAn, Tonglu, Jiande) and rural (ChunAn) stations in the Yangtze River Delta region, eastern China. The aerosol optical depth (AOD) varied from 0.68 to 0.76, with two peaks in June and September, and decreased from the eastern coast to western inland areas. The ratio of the AOD of fine-mode particles to the total AOD was > 0.90 and the extinction Angström exponent was > 1.20 throughout the year at all seven sites. The Moderate Resolution Imaging Spectroradiometer (MODIS) C6 retrieval AOD was validated by comparison with ground-based observations. The correlation coefficients (R2) between the MODIS C6 AOD data and the values measured on the ground were ~ 0.73–0.89. The single-scattering albedo varied from 0.91 to 0.94, indicating that scattering aerosol particles are dominant in this region. The real parts of the refractive index were ~ 1.41–1.43, with no significant difference among the seven urban, suburban and rural sites. Large imaginary parts of the refractive index were seen in August at all urban, suburban and rural sites. The fine-mode radii in the Yangtze River Delta region were ~ 0.2–0.3 μm with a volume of 0.10–0.12 μm3 and the coarse-mode radii were ~ 2.0 μm with a volume close to 0.07 μm3. The fine-mode aerosols were obviously larger in June and September than in other months at almost the sites. The absorption AOD was low in the winter. The absorption Angström exponent and the extinction Angström exponent were used to classify the different types of aerosol and the components of mixtures. The aerosols caused negative radiative forcing both at the Earth's surface and at the top of the atmosphere all year round in the Yangtze River Delta region of eastern China.

The daily values of UVB irradiation (290–315 nm), IUVB, and the broadband total irradiation (300–2800 nm), IT, measured on a horizontal plane have been correlated for the period 2000–2008 at 16 measurement sites in Spain. The results have been compared with the daily experimental values registered at the same sites during the period 2009–2011. The coefficients of determination R2 obtained by applying a linear regression are higher than 0.88 for all sites and increase to 0.94 when using a quadratic regression. When all data are considered together, the values of R2 are 0.91 and 0.97 for the linear and quadratic regressions, respectively. Three different clearness indices, which are dimensionless parameters, have been also used in order to reduce the uncertainties of the estimations and to reduce the local nature of the coefficients: (1) the UVB clearness index, kTUVB = IUVB/I0UVB; (2) the modified UVB clearness index, k′TUVB and (3) the estimated UVB clearness index, k*TUVB. The results show a strong dependence on the solar zenith angle. The bi-dimensional regression of kTUVB as a function of the solar zenith angle and the clearness index, kT, substantially improves the correlation, with R2 values higher than 0.81 for all sites. Finally, a formula relating kTUVB and kT, valid for latitudes between 36°N and 44°N, has been obtained: kTUVB = 0.064 kT – 0.0011 θz – 1.24 E-05 ϕ + 7.6 E-05 λ + 0.063, where θz represents the solar zenith angle (in degrees), ϕ is the latitude (in degrees) of the site and λ is the distance to the sea (in km). We have compared the experimental values for the period 2009–2011 with those estimated using this expression. For this, the coefficient of determination (R2) is 0.87, with a MBD of –3.4%, a RMSE of 21% and a NRMSE of 8.7%.

This study analyzes the atmospheric particles concentration at ground level during a severe pollution event that took place in Valencia (Spain) from 7 to 12 February 2011. The episode was related to a subtropical anticyclone system that affected the Iberian Peninsula and western Europe. The dominant anticyclone imposed an extended low gradient pressure system and a low mixing layer height in the region that caused the accumulation of pollutants over the western Mediterranean. Moreover, the stagnant conditions led to the formation of the local sea breeze, accompanied by an increase of relative humidity and the decrease of ambient temperature. Our study is mainly focused on the analysis of particulate matter levels (PM10 and PM2.5) and the concentration of black carbon (BC) measured at the Burjassot station, Valencia (Spain). BC and PM levels were found to steadily increase during the event (from 3.2 μg/m 3 and 33 μg/m 3 before the event to 4.9 μg/m 3 and 61 μg/m 3 for BC and PM2.5, respectively) and abruptly decreased to 1.3 μg/m 3 and 14 μg/m 3 , respectively, after a cold front swept the Iberian Peninsula, bringing fresh air from the Atlantic and increasing the mixing layer height, thus ventilating and diluting the accumulated pollutants. As a consequence, the EU limit of 50 μg/m 3 for PM10 size fraction was exceeded during days 7 to 12 February 2011 at Valencia, Spain.

The Surface Processes and Ecosystem Changes Through Response Analysis (SPECTRA) Barrax Campaigns were validation campaigns developed in the framework of the SPECTRA mission in order to verify that the geophysical data products provided by satellite imagery are consistent with the measurements made by independent means. Two campaigns took place in Barrax, Spain, during the summers of 2003 and 2004. This paper presents the results of the characterization of the atmospheric composition from solar radiation, radiosoundings, and lidar measurements. Several potentially interesting situations involving atmospheric layers with different types of aerosols and water content are discussed. The presence of a residual layer capping the mixing layer during some days of the 2003 campaign and the arrival of a dust-rich air mass from the Sahara on the last two days of the 2004 campaign provide some relevant aerosol vertical profiles to test atmospheric correction algorithms. The study of the effects of these atmospheric situations on radiative transfer calculations is required in the development and validation of advanced atmospheric correction codes for the new generation of Earth Observation Systems. © 2007 IEEE.

The European Skynet Radiometers network (EuroSkyRad or ESR) has been recently established as a research network of European PREDE sun-sky radiometers. Moreover, ESR is federated with SKYNET, an international network of PREDE sun-sky radiometers mostly present in East Asia. In contrast to SKYNET, the European network also integrates users of the CIMEL CE318 sky–sun photometer. Keeping instrumental duality in mind, a set of open source algorithms has been developed consisting of two modules for (1) the retrieval of direct sun products (aerosol optical depth, wavelength exponent and water vapor) from the sun extinction measurements; and (2) the inversion of the sky radiance to derive other aerosol optical properties such as size distribution, single scattering albedo or refractive index. In this study we evaluate the ESR direct sun products in comparison with the AERosol RObotic NETwork (AERONET) products. Specifically, we have applied the ESR algorithm to a CIMEL CE318 and PREDE POM simultaneously for a 4-yr database measured at the Burjassot site (Valencia, Spain), and compared the resultant products with the AERONET direct sun measurements obtained with the same CIMEL CE318 sky–sun photometer. The comparison shows that aerosol optical depth differences are mostly within the nominal uncertainty of 0.003 for a standard calibration instrument, and fall within the nominal AERONET uncertainty of 0.01–0.02 for a field instrument in the spectral range 340 to 1020 nm. In the cases of the Ångström exponent and the columnar water vapor, the differences are lower than 0.02 and 0.15 cm, respectively. Therefore, we present an open source code program that can be used with both CIMEL and PREDE sky radiometers and whose results are equivalent to AERONET and SKYNET retrievals.

In this work, we present a simple model that allows us to easily obtain the character of the dominant air mass for any location in the Northern Hemisphere at any time. Specifically, in this article the model has been tested at Valencia, Spain, for the years from 2006 to 2009. The classification of the air masses is performed analysing their trajectories over pre-defined source regions in the Northern Hemisphere. Daily trajectories were simulated by the hybrid single-particle Lagrangian integrated trajectory model HYSPLIT and then classified by our model. In order to verify our classification results, those cases identified as African were compared with the Saharan dust intrusions reported for Valencia by the Ministerio de Medio Ambiente y Medio Rural y Marino MARM in collaboration with the Centro Superior de Investigaciones Cientificas CSIC. The model we present in this article can be applied in the selection of an optimum aerosol model for the atmospheric correction of remote sensing products.

During the 2002 summer, the VELETA 2002 field campaign has been carried out at the Sierra Nevada Massif, close to Granada in South-Eastern Spain. During the campaign, CIMEL CE-318 robotic radiometer has been one of the key instruments in the characterization of the atmospheric aerosol columnar properties. This kind of radiometers have been operated at Motril, a coastal location at sea level, Pitres (1200 m a.s.l.), located in the South slope of Sierra Nevada Massif, Las Sabinas (2200m a.s.l.), located on the north slope of the mountain range, and Armilla (680m a.s.l.), located in the valley. The principal feature of the locations is that they provide a strong altitudinal gradient. This work presents the evolution of changes followed by the atmospheric aerosol in the vertical column. Columnar aerosol properties have been derived from the CIMEL CE-318 measurements obtained at the four stations. In this sense, the combination of solar direct measurements and sky radiances were used to retrieve the aerosol columnar size distributions by means of Nakajima's code. Marked changes in the atmospheric aerosol along the campaign have been explained in terms of the synoptic conditions. A detailed study of the columnar properties at the different places has been done. Changes in the spectral dependence of the single scattering albedo under the influence of different air masses have been discussed. The size distributions have been fitted to a bimodal lognormal distribution function model, and the associated parameters have been correlated with aerosol optical depth or Angstrom exponent. In some cases, it has been necessary to develop different correlations for cases affected or non-affected by the arrival of Saharan dust. In the case of Armilla (680 m a.s.l.) and Las Sabinas (2200 m a.s.l.), the small horizontal distance allow us to consider that both stations are representative of the same atmospheric column, a fact that has been used to analyse the daily evolution of the mixing layer in the north slope. (C) 2007 Elsevier Ltd. All rights reserved.

The Fennec climate programme aims to improve understanding of the Saharan climate system through a synergy of observations and modelling. We present a description of the Fennec airborne observations during 2011 and 2012 over the remote Sahara (Mauritania and Mali) and the advances in the understanding of mineral dust and boundary layer processes they have provided. Aircraft instrumentation aboard the UK FAAM BAe146 and French SAFIRE (Service des Avions Français Instrumentés pour la Recherche en Environnement) Falcon 20 is described, with specific focus on instrumentation specially developed for and relevant to Saharan meteorology and dust. Flight locations, aims and associated meteorology are described. Examples and applications of aircraft measurements from the Fennec flights are presented, highlighting new scientific results delivered using a synergy of different instruments and aircraft. These include (1) the first airborne measurement of dust particles sizes of up to 300 microns and associated dust fluxes in the Saharan atmospheric boundary layer (SABL), (2) dust uplift from the breakdown of the nocturnal low-level jet before becoming visible in SEVIRI (Spinning Enhanced Visible Infra-Red Imager) satellite imagery, (3) vertical profiles of the unique vertical structure of turbulent fluxes in the SABL, (4) in situ observations of processes in SABL clouds showing dust acting as cloud condensation nuclei (CCN) and ice nuclei (IN) at −15 °C, (5) dual-aircraft observations of the SABL dynamics, thermodynamics and composition in the Saharan heat low region (SHL), (6) airborne observations of a dust storm associated with a cold pool (haboob) issued from deep convection over the Atlas Mountains, (7) the first airborne chemical composition measurements of dust in the SHL region with differing composition, sources (determined using Lagrangian backward trajectory calculations) and absorption properties between 2011 and 2012, (8) coincident ozone and dust surface area measurements suggest coarser particles provide a route for ozone depletion, (9) discrepancies between airborne coarse-mode size distributions and AERONET (AERosol Robotic NETwork) sunphotometer retrievals under light dust loadings. These results provide insights into boundary layer and dust processes in the SHL region – a region of substantial global climatic importance.

In this paper we present the results obtained from ground-based measurements using a CIMEL sunphotometer during selected clear days corresponding to the winter and summer periods of 2002 in Valencia, an urban coastal Mediterranean site. From the direct solar extinction data the spectral aerosol optical depth (AOD) has been retrieved. This spectral AOD has been used to obtain the size distribution function from the King inversion algorithm. The results show the great dependence of the optical aerosol characteristics on the dominant winds in this area. This location is subject to winds which have either a land or Mediterranean origin which frequently mask the aerosols coming from the Atlantic or north Africa, respectively.

An analysis is made of the UV Index (UVI) obtained from the ultraviolet erythemal solar radiation (UVER) data measured by the Spanish UVB Radiometric Network between the years 2000 and 2009. Previously, the daily UVI has been evaluated using two different criteria: (a) the value corresponding to solar noon; and (b) the daily maximum value. The mean percentage of agreement is 92% if we consider the cases for which the difference is zero or one UVI unit. These results are similar to those obtained in a previous work where only 2 years were analyzed. In all the stations the UVI reaches very high values (8-10) in spring-summer, and the very high and extreme (≥ 11) UVI values are more dependent on the continental effect than on the latitude effect. From the UVI values it is possible to classify the stations into four groups: Coastal stations, Continental stations (more than 200 km from the coast), Southern stations (Coastal stations but with similar values of UVI as the Continental ones due to their low latitude) and Canary Islands stations (1400 km southwest from the Iberian Peninsula thus lower latitude). The monthly mean maximum of UVI is reached in July due to the annual evolution of the total ozone column. This value corresponds, for a skin phototype II, to three times the minimal erythemal dose (MED) in an hour in a Coastal station, 3.5 MEDs in an hour measured in a Continental or Southern station and up five MEDs in an hour in the Izana station (Canary Islands). The cumulative dose on a horizontal plane over an average year has been calculated for each station. More than 40% of the annual dose is received in summer, about 35% in spring, more than 11% in autumn and less than 10% in winter except for the stations in the Canary Islands where the difference between seasons is less significant.

The European Skynet Radiometers network (EuroSkyRad or ESR) has been recently established as a research network of European Prede POM sun – sky radiometers. Moreover, ESR is federated with SKYNET (SKYrad NETwork), an international network mostly present in East Asia. In contrast to SKYNET, the European network also integrates users of the Cimel CE318 sunphotometer. Keeping instrumental duality in mind, a set of open source algorithms has been developed consisting of two modules for: (1) the retrieval of direct sun products from the sun extinction measurements; and (2) the inversion of the sky radiance to derive aerosol optical properties. In this study we evaluate the ESR direct sun products (spectral aerosol optical depth, Angström wavelength exponent and columnar content of water vapour) in comparison with the AERosol RObotic NETwork (AERONET) products. Specifically, we have applied the ESR algorithm to a Cimel CE318 and Prede POM01L simultaneously for a 4 yr database measured at the Burjassot site (Valencia, Spain), and compared the resultant products with the AERONET direct sun retrievals obtained with the same Cimel CE318 instrument. The comparison show that aerosol optical depth differences are mostly within the nominal uncertainty of 0.003 for a standard calibration instrument, and fall within the nominal AERONET uncertainty of 0.01–0.02 for a field instrument. Therefore, we present an open source code that can be used for both radiometers and whose results are comparable to those of AERONET and SKYNET.

Although routinely monitored by ground based air quality networks, the particulate matter distribution could be eventually better described with remote sensing techniques. However, valid relationships between ground level and columnar ground based quantities should be known beforehand. In this study we have performed a comparison between particulate matter measurements at ground level at different cut sizes (10, 2.5 and 1.0 mm), and the aerosol optical depth obtained by means of a ground based sunphotometer during a multiinstrumental field campaign held in El Arenosillo (Huelva, Spain) from 28 June to 4 July 2006. All the PM fractions were very well correlated with AOD with correlation coefficients that ranged from 0.71 to 0.81 for PM10, PM2.5 and PM1. Furthermore, the influence of the mixing layer height in the correlations was explored. The improvement in the correlation when the vertical distribution is taken into account was significant for days with a homogeneous mixing layer. Moreover, the chemical analysis of the individual size fractions allowed us to study the origin of the particulate matter. Secondary components were the most abundant and also well correlated in the three size fractions; but for PM10 fraction, chemical species related to marine origin were best correlated. Finally, we obtained a relationship between MODIS L3 AOD from collection 5.1 and the three PM cut sizes. In spite of being a relatively clean environment, all the techniques were able to capture similar day to day variations during this field campaign.

A Microtops II "ozone monitor" with UV channels centered at 305.5, 312.5, and 320 nm has been used routinely in six experimental campaigns carried out in several geographic locations and seasons, covering latitudes from 35 to 68° N during the last ten years (2001–2011). The total ozone content is retrieved by Microtops II by using different combinations (Channel I, 305.5/312.5 nm; Channel II, 312.5/320 nm; and Channel III, 305.5/312.5/320 nm) of the signals at the three ultraviolet wavelengths. The long-term performance of the total ozone content determination has been studied taking into account the sensitivities to the calibration, airmass, temperature and aerosols. When a calibration was used and the airmass limit was fixed to 3, the root mean square deviations of the relative differences produced by Microtops II with respect to several Brewers are 0.9, 2, and 2% respectively for the Channel I, Channel II, and Channel III retrieval. The performance of the Microtops retrieval has been stable during the last ten years. Channel I represents the best option to determine the instantaneous total ozone content. Channels II and III values appear weakly sensitive to temperature, ozone content, and aerosols. Channel II is more stable than Channel I for airmasses larger than 2.6. The conclusions do not show any dependence on latitude and season. This study was possible thanks to a postdoctoral fellowship funded by the Generalitat Valenciana in the case of J. L. G´omez Amo (in the framework of “Estancies postdoctorals en centres de Excellencia de la Comunitat Valenciana” programme) and a Juan de la Cierva research contract (JCI-2009-04455) in the case of V. Estell´es, funded by the Spanish Ministry of Science and Innovation (MICINN). This work was also supported by the MICINN projects CGL2007-60648 and CGL2009-07790, and by the Valencian Autonomous Government through the Project PROMETEO/2010/064.

SKYNET is an international research network of ground based sky – sunphotometers for the observation and monitoring of columnar aerosol properties. The algorithm developed by SKYNET is called SKYRAD.pack, and it is used on Prede instruments only. In this study, we have modified the SKYRAD.pack software in order to adapt it to Cimel sunphotometers. A one month database of Cimel data obtained at Burjassot (Valencia, Spain) has been processed with this program and the obtained inversion products have been compared with AERONET retrievals. In general, the differences found were consistent with the individual error assessments for both algorithms. Although the aerosol optical depth compared well for any aerosol burden situation (rmsd of 0.002–0.013 for all wavelengths), inversion products such as the single scattering albedo, refractive index and asymmetry parameter compared better for higher turbidity situations. The comparison performed for cases with an aerosol optical depth at 440 nm over 0.2 showed rms differences of 0.025–0.049 for single scattering albedo, 0.005–0.034 for the real part of refractive index, 0.004–0.007 for the imaginary part of the refractive index and 0.006–0.009 for the asymmetry parameter. With respect to the volume distributions, the comparison also showed a good agreement for high turbidity cases (mainly within the 0.01–7 μm interval) although the already known discrepancy in the extremes of the distribution was still found in 40% of the cases, in spite of eliminating data and instrumental differences present in previous studies.

Euroskyrad (ESR) is a network of European groups that focus their research on the atmospheric aerosols by applying the Skyrad inversion algorithm indistinctly to Cimel CE318 and Prede POM sky - sun radiometers. This study addresses the performance of ESR new algorithms in comparison to AERONET for aerosol optical depth retrieval from direct sun measurements. More specifically, we have applied the ESR algorithms (ESR.pack, modes 1 and 2) to a Cimel CE318 and Prede POM-OIL simultaneous database obtained at Valencia (Spain) and compared the resultant aerosol optical depth with the AERONET retrievals. The results obtained with Cimel agree with AERONET within 0,009 - 0,011 and 0,001 - 0,007 (ESR modes 1 and 2, respectively) depending on wavelength. Furthermore, a comparison between aerosol optical depth obtained from Cimel and Prede radiometers is also possible by using the same code, and the results agree better than 0,003 - 0,006 independently of ESR mode. Finally, the comparison of AOD obtained with Prede/ESR against Cimel/AERONET shows a reasonable deviation for mode 1 (0,006 - 0,012) and a very good agreement for mode 2 (0,004 - 0,007). In general these differences fall within the nominal AERONET uncertainty of 0.01-0.02 for field instruments. © 2010 SPIE.

The European Space Agency carried out the Sentinel-2 and Fluorescence Experiment (SEN2FLEX) campaign in Barrax (Spain) during the summer of 2005, with the main objective of observe solar induced fluorescence signal using the AirFLEX airborne instrument over different vegetation targets in order to verify signal suitability for observations from space as proposed in the FLEX mission. A highly precise atmospheric correction is mandatory for adequate measurements of the AirFLEX instrument; thus a complete characterization of the atmosphere was programmed in SEN2FLEX in order to document the presence of atmospheric aerosols above the experimental area, as their effects represent the major source of uncertainty in atmospheric correction algorithms. In this work, an analysis of the atmospheric data is presented focusing on its eventual application to atmospheric correction of satellite imagery. Validation of Compact Airborne Spectrographic Imager (CASI) aerosol optical depth and columnar water vapor content retrievals has been included as an example of application to remote sensing products. A relevant feature was the arrival of a Saharan dust intrusion from 13 to 15 July, yielding the increase of aerosol optical depth at 550 nm from 0.1 to 0.5 because of changes in the vertical distribution of aerosols, with a transport layer located between 1.5 and 4 km. An accurate knowledge of these aerosol features will be relevant in future implementation of atmospheric correction code of the airborne and satellite hyperspectral imagery. Copyright 2008 by the American Geophysical Union.

[1] Measurements of diffuse UV erythemal radiation (UVER) using a shadowband have been corrected using the models proposed by Drummond (1956), LeBaron et al. (1990), and Batlles et al. (1995). Two different methods were used to validate these models: intercomparison with an Optronic OL754 spectroradiometer and comparison with the values simulated by two radiative transfer codes, SMARTS and SBDART. For this comparison only clear days have been used. The corrected experimental values were analyzed in order to study the average values of the diffuse UVER fraction in relation to the clearness index kt. These varied between 62%, for kt close to 0.8, and 93% for kt of 0.2–0.3. Finally, a study of the monthly average and extreme values of the UV Index for diffuse radiation is presented, showing a maximum value of 6 in June.

In this paper, we present a climatological study of atmospheric aerosols in coastal eastern Spain, by means of experimental measurements using a Cimel CE318-2 Sun photometer. The aerosol optical depth, Ångström wavelength exponent, size distribution, complex refractive index, asymmetry parameter, and single scattering albedo have been retrieved from these measurements. The columnar water content, as an important parameter for understanding aerosol growth, has also been retrieved. Statistical results of the annual and seasonal variability analysis, mainly related to the usual summer maximum turbidity found in the Mediterranean and European regions, are also shown. The results are linked to the character of the site, located in an urban environment, near the Mediterranean Sea, and frequently affected by dusty air masses of Saharan origin. Copyright 2007 by the American Geophysical Union.

In July 2002 the VELETA-2002 field campaign was held in Sierra Nevada (Granada) in the south of Spain. The main objectives of this field campaign were the study of the influence of elevation and atmospheric aerosols on measured UV radiation. In the first stage of the field campaign, a common calibration and intercomparison between Licor-1800 spectroradiometers and Cimel-318 Sun photometers was performed in order to assess the quality of the measurements from the whole campaign. The intercomparison of the Licor spectroradiometers showed, for both direct and global irradiances, that when the comparisons were restricted to the visible part of the spectrum the deviations were within the instruments’ nominal accuracies which allows us to rely on these instruments for measuring physical properties of aerosols at the different measurement stations. A simultaneous calibration on AOD data was performed for the Cimel-318 Sun photometers. When a common calibration and methodology was applied, the deviation was lowered to much less than 0.01 for AOD. At the same time an intercomparison has been made between the AOD values given by the spectroradiometers and the Sun photometers, with deviations obtained from 0.01 to 0.03 for the AOD in the visible range, depending on the channel. In the UVA range, the AOD uncertainty was estimated to be around 0.02 and 0.05 for Cimel and Licor respectively. In general the experimental differences were in agreement with this uncertainty estimation. In the UVB range the AOD measurements should not be used due to maximum instrumental uncertainties. This work was financed by CICYT-MCYT through the Coordinated Project CLI2000-0903.

[1] A study has been made of the column aerosols using solar irradiance extinction measurements at ground level in a boreal region (Sodankyla, Finland) during spring 2002. The aerosol properties have been related to air mass origin. In general, the aerosol levels were observed to be very low, independent of the air mass origin, with an aerosol optical depth (AOD) value at 500 nm of less than 0.09 ± 0.03. Two characteristic patterns were observed depending on whether the air masses originated in the north and west or from the south and east. In the first case (north and west origins) the aerosol load was very small, with very low optical depths in the range 0.03 ± 0.02 to 0.09 ± 0.03 for 500 nm wavelengths. The size distribution usually showed two modes, with a strong contribution from the large-particle mode, probably a consequence of the presence of maritime-type particles originating in the ocean. When the air masses originated from a south or east direction, the behavior was the opposite to that noted before. In these cases the AOD was rather larger, above all for air masses originating in central Europe and Russia with an average value at 500 nm of 0.14 ± 0.02.

The capability to monitor and predict the physical characteristics of the atmosphere has been largely improved last decades. Aerosol optical thickness (AOT) and precipitable water vapor amount (W) are crucial atmospheric parameters in the understanding of atmospheric dynamics, as well as for the atmospheric correction of optical remote sensing images to be employed for land and water management. The objective of this work has been to adopt a methodology for measuring the water vapor and aerosol optical thickness in the atmospheric column by means of a Fieldspec Pro FR spectroradiometer. These measurements will be later useful for improving accuracy and helping to interpret remote sensing data, not only in the SPARC 2004 field campaign but for other future field campaigns aimed at land management. The methodology is based on two well‐known techniques of sun photometry: the inversion of sun direct irradiance for AOT and split window, for precipitable water vapor. The direct solar irradiance were acquired si...

The Eyjafjallajökull ash that crossed over Spain and Portugal on 6e12 May 2010 has been monitored by a set of operational sun photometer sites within AERONET-RIMA and satellite sensors. The sun photometer observations (aerosol optical depth, coarse mode concentrations) and ash products from IASI and SEVIRI satellite sensors, together with FLEXPART simulations of particle transport, allow identifying the volcanic aerosols. The aerosol columnar properties derived from inversions were investigated, indicating specific properties, especially regarding the absorption. The single scattering albedo was high (0.95 at 440 nm) and nearly wavelength independent, although with slight decrease with wavelength. Other parameters, like the fine mode fraction of the volume size distributions (0.20e0.80) or the portion of spherical particles (15e90%), were very variable among the sites and indicated that the various ash clouds were inhomogeneous with respect to particle size and shape.