Suchergebnisse

A sensitivity study of aerosol retrievals to the geometrical configuration of the ground-based sky radiometer observations is carried out through inversion tests. Specifically, this study is focused on principal plane and almucantar observations, since these geometries are employed in AERONET (AErosol RObotic NETwork). The following effects have been analyzed with simulated data for both geometries: sensitivity of the retrieval to variability of the observed scattering angle range, uncertainties in the assumptions of the aerosol vertical distribution, surface reflectance, possible instrument pointing errors, and the effects of the finite field of view. ; Financial support was provided by the Spanish CICYT (CGL2009-09740 and CGL2011-23413, CGL2011-13085-E). The research leading to these results was supported by funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 262254 [ACTRIS]. We also thank the Environmental Council of the CyL Regional Government (Consejería de Medio Ambiente, Junta de Castilla y León) for supporting this research.

A sensitivity study of aerosol retrievals to the geometrical configuration of the ground-based sky radiometer observations is carried out through inversion tests. Specifically, this study is focused on principal plane and almucantar observations, since these geometries are employed in AERONET (AErosol RObotic NETwork). The following effects have been analyzed with simulated data for both geometries: sensitivity of the retrieval to variability of the observed scattering angle range, uncertainties in the assumptions of the aerosol vertical distribution, surface reflectance, possible instrument pointing errors, and the effects of the finite field of view. ; Financial support was provided by the Spanish CICYT (CGL2009-09740 and CGL2011-23413, CGL2011-13085-E). The research leading to these results was supported by funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 262254 [ACTRIS]. We also thank the Environmental Council of the CyL Regional Government (Consejería de Medio Ambiente, Junta de Castilla y León) for supporting this research.

This study evaluates the potential of using aerosol optical depth (τa) measurements to characterize the microphysical and optical properties of atmospheric aerosols. With this aim, we used the recently developed GRASP (Generalized Retrieval of Aerosol and Surface Properties) code for numerical testing of six different aerosol models with three different aerosol loads. We found that bimodal log-normal size distributions serve as useful input assumptions, especially when the measurements have inadequate spectral coverage and/or limited accuracy, such as lunar photometry. The direct numerical simulations indicate that the GRASP-AOD retrieval provides modal aerosol optical depths (fine and coarse) to within 0.01 of the input values. The retrieval of the fine mode radius, width, and volume concentration is stable and precise if the real part of the refractive index is known (.) ; The research has been supported by the Labex CaPPA: the CaPPA project (Chemical and Physical Properties of the Atmosphere) is funded by the French National Research Agency (ANR) through the PIA (Programme d'Investissement d'Avenir) under contract "ANR-11-LABX-0005-01" and by the Regional Council "Nord Pas de Calais - Picardie" and the European Funds for Regional Economic Development (FEDER). This research has also received funding from the French National Research Agency (ANR) project ADRIMED (contract ANR-11-BS56- 0006). The authors acknowledge the funding provided by the European Union (H2020-INFRAIA-2014-2015) under Grant Agreement No. 654109 (ACTRIS-2). Financial support was also provided by MINECO (CTM2015-66742-R).

Sensitivity studies indicate that among the diverse error sources of ground-based sky radiometer observations, the pointing error plays an important role in the correct retrieval of aerosol properties. The accurate pointing is specially critical for the characterization of desert dust aerosol. The present work relies on the analysis of two new measurement procedures (cross and matrix) specifically designed for the evaluation of the pointing error in the standard instrument of the Aerosol Robotic Network (AERONET), the Cimel CE-318 Sun photometer. The first part of the analysis contains a preliminary study whose results conclude on the need of a Sun movement correction for an accurate evaluation of the pointing error from both new measurements. ; We thank the AERONET, PHOTONS, RIMA and WRC staff for their scientifc and technical support. Financial support was provided by: the Spanish CICYT (CGL2009- 09740 and CGL2011-23413, CGL2011-13085-E). The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007–2013) under grant agreement Nr. 262254 [ACTRIS].

Comunicación presentada en: 2012 European Aerosol Conference (EAC-2012), B-WG01S2P30, celebrada del 2 al 7 de septiembre de 2012 en Granada. ; This work has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement N. 262254. Financial support from the Spanish Ministry of Science (MICINN) under projects with ref. CGL2009-09740, CGL2011-23413, CGL2010-09480-E and CGL2011-13085-E as well as from Junta de Castilla y León are gratefully acknowledged.

This work involves a first analysis of the systematic errors observed in the AOD retrieved at nighttime using the Sun–sky–lunar CE318-T photometer. In this respect, this paper is a first attempt to correct the AOD uncertainties that currently affect the lunar photometry by means of an empirical regression model. We have detected and corrected an important bias correlated to the Moon's phase and zenith angles, especially at longer wavelength channels. ; AERONET Sun photometers at Izaña have been calibrated within the AERONET Europe TNA, supported by the European Union's Horizon 2020 research and innovation program under grant agreement no. 654109 (ACTRIS-2).

Sensitivity studies indicate that among the diverse error sources of ground-based sky radiometer observations, the pointing error plays an important role in the correct retrieval of aerosol properties. The accurate pointing is specially critical for the characterization of desert dust aerosol. The present work relies on the analysis of two new measurement procedures (cross and matrix) specifically designed for the evaluation of the pointing error in the standard instrument of the Aerosol Robotic Network (AERONET), the Cimel CE-318 Sun photometer. The first part of the analysis contains a preliminary study whose results conclude on the need of a Sun movement correction for an accurate evaluation of the pointing error from both new measurements. Once this correction is applied, both measurements show equivalent results with differences under 0.01° in the pointing error estimations. The second part of the analysis includes the incorporation of the cross procedure in the AERONET routine measurement protocol in order to monitor the pointing error in field instruments. The pointing error was evaluated using the data collected for more than a year, in 7 Sun photometers belonging to AERONET sites. ; We thank the AERONET, PHOTONS, RIMA and WRC staff for their scientific and technical support. Financial support was provided by the Spanish CICYT (CGL2009-09740 and CGL2011-23413, CGL2011-13085-E). The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 262254 [ACTRIS].

The aim of this paper is to analyze the suitability of the high-mountain stations Mauna Loa and Izaña for Langley plot calibration of Sun photometers. Thus the aerosol optical depth (AOD) characteristics and seasonality, as well as the cloudiness, have been investigated in order to provide a robust estimation of the calibration uncertainty as well as the number of days that are suitable for Langley calibrations. The data used for the investigations belong to the AERONET and GAW-PFR networks, which maintain reference Sun photometers at these stations with long measurement records: 22 years at Mauna Loa and 15 years at Izaña. In terms of clear-sky and stable aerosol conditions, Mauna Loa (3397ma.s.l.) exhibits on average 377 Langley plots (243 morning and 134 afternoon) per year suitable for Langley plot calibration, whereas Izaña (2373ma.s.l.) shows 343 Langley plots (187 morning and 155 afternoon) per year. The background AOD (500nm) values, on days that are favorable for Langley calibrations, are in the range 0.01–0.02 throughout the year, with well-defined seasonality that exhibits a spring maximum at both stations plus a slight summer increase at Izaña. The statistical analysis of the long-term determination of extraterrestrial signals yields to a calibration uncertainty of ∼ 0.25–0.5%, this uncertainty being smaller in the visible and near-infrared wavelengths and larger in the ultraviolet wavelengths. This is due to atmospheric variability produced by changes in several factors, mainly the AOD. The uncertainty cannot be reduced based only on quality criteria of individual Langley plots and averaging over several days is shown to reduce the uncertainty to the needed levels for reference Sun photometers. ; This research has received funding from the European Union's Horizon 2020 Research and Innovation Programme under grant agreement no. 654109 (ACTRIS-2). The funding by MINECO (CTM2015-66742-R) and Junta de Castilla y León (VA100P17) is also acknowledged.

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. ; This work has been supported by EU-project Monitoring Atmospheric Composition and Climate (MACC-II) under the European Union Seventh Framework Programme, grant agreement number 283576. J. M. Baldasano and S. Basart acknowledge the Severo Ochoa (SEV-2011-00067) program of the Spanish Government and the mobility program from the Catalan Government (BE-DGR 2012).

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. ; This work has been supported by EU-project Monitoring Atmospheric Composition and Climate (MACC-II) under the European Union Seventh Framework Programme, grant agreement number 283576. J. M. Baldasano and S. Basart acknowledge the Severo Ochoa (SEV-2011-00067) program of the Spanish Government and the mobility program from the Catalan Government (BE-DGR 2012).

The use of sky cameras for nocturnal aerosol characterization is discussed in this study. Two sky cameras are configured to take High Dynamic Range (HDR) images at Granada and Valladolid (Spain). Some properties of the cameras, like effective wavelengths, sky coordinates of each pixel and pixel sensitivity, are characterized. After that, normalized camera radiances at lunar almucantar points (up to 20° in azimuth from the Moon) are obtained at three effective wavelengths from the HDR images. These normalized radiances are compared in different case studies to simulations fed with AERONET aerosol information, giving satisfactory results. The obtained uncertainty of normalized camera radiances is around 10% at 533 nm and 608 nm and 14% for 469 nm. Normalized camera radiances and six spectral aerosol optical depth values (obtained from lunar photometry) are used as input in GRASP code (Generalized Retrieval of Aerosol and Surface Properties) to retrieve aerosol properties for a dust episode over Valladolid. The retrieved aerosol properties (refractive indices, fraction of spherical particles and size distribution parameters) are in agreement with the nearest diurnal AERONET products. The calculated GRASP retrieval at night time shows an increase in coarse mode concentration along the night, while fine mode properties remained constant. ; This work was supported by the Andalusia Regional Government(project P12-RNM-2409) and by the"Consejería de Educación, Juntade Castilla y León"(project VA100U14); the Spanish Ministry of Econo-my and Competitiveness and FEDER funds under the projects CGL2013-45410-R, CMT2015-66742-R, CGL2016-81092-R and"Juan de la Cierva Formación"program (FJCI-2014-22052); and the European Union's Ho-rizon 2020 research and innovation programme through projectACTRIS-2 (grant agreement No 654109).

Aerosol pollution in eastern China is an unfortunate consequence of the region's rapid economic and industrial growth. Here, sun photometer measurements from seven sites in the Yangtze River Delta (YRD) from 2011 to 2015 were used to characterize the climatology of aerosol microphysical and optical properties, calculate direct aerosol radiative forcing (DARF) and classify the aerosols based on size and absorption. Bimodal size distributions were found throughout the year, but larger volumes and effective radii of fine-mode particles occurred in June and September due to hygroscopic growth and/or cloud processing. Increases in the fine-mode particles in June and September caused AOD440 nm > 1.00 at most sites, and annual mean AOD440 nm values of 0.71–0.76 were found at the urban sites and 0.68 at the rural site. Unlike northern China, the AOD440 nm was lower in July and August (∼ 0.40–0.60) than in January and February (0.71–0.89) due to particle dispersion associated with subtropical anticyclones in summer. Low volumes and large bandwidths of both fine-mode and coarse-mode aerosol size distributions occurred in July and August because of biomass burning. Single-scattering albedos at 440 nm (SSA440 nm) from 0.91 to 0.94 indicated particles with relatively strong to moderate absorption. ; This work was supported by a grant from the National Key R & D Program Pilot Projects of China (2016YFA0601901), the National Natural Science Foundation of China (41590874, 41475138 & 41375153), the Natural Science Foundation of Zhejiang Province (LY16010006), the CAMS Basis Research Project (2016Z001 & 2014R17), the Climate Change Special Fund of CMA (CCSF201504), the Special Project of Doctoral Research supported by Liaoning Provincial Meteorological Bureau (D201501), the Hangzhou Science and Technology Innovative project (20150533B17) and the European Union Seventh Framework Programme (FP7/2007–2013) under grant agreement no. 262254.