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Abstract: Understanding the chemical character of organic aerosols is extremely important for evaluating their role in climate forcing and human respiratory health. Aerosol columnar properties retrieved by sun photometry represent a large dataset of information about the physical and light absorbing and scattering properties of the total aerosol, but lack more detailed chemical information about the organic fraction of atmospheric particulate matter. To obtain additional information about relationships between organic aerosol sources and columnar properties, we simultaneously examined stable isotope properties of PM10 aerosols from urban (Granada, Spain) and remote (Sierra Nevada, Spain) sites and diesel exhaust, spectroscopic properties of water soluble organic carbon (WSOC) of PM10 aerosols, and sun photometry measurements. We demonstrated that C and N stable isotopes and parameters from UV–vis and fluorescence spectroscopy are able to discriminate between aerosols receiving substantial fossil fuel pollution and those influenced by Saharan dust in an urban area. More depleted δ13C was associated with low asymmetry parameter, gλ, and high values of the spectral slope ratio, SR, were associated with high effective radius, typical of pollution situations. The humification index (HIX), used predominantly to evaluate the degree of organic matter humification, was significantly related to gλ and the radius of fine mode particles, rf, and may reflect aging of the Saharan dust-influenced aerosols. Parallel factor analysis (PARAFAC) modeling identified a fluorescent component (C3) with a spectrum similar to that of naphthalene, which was significantly related to gλ and rf. The diesel exhaust sample represented a pollution end-member, with the lightest δ13C value (−26.4‰), lowest SR (0.95), lowest HIX (2.77) and highest %C3 (20%) of all samples. [Copyright &y& Elsevier]

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 (1200m 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 Ångström 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 (680m a.s.l.) and Las Sabinas (2200m 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. [Copyright &y& Elsevier]

The All-Sky Imager developed by the Atmospheric Physics Group has been tested for aerosol characterization. Different neural network-based models calculate the aerosol optical depth (AOD) for two wavelengths and the Ångström turbidity parameter α using as input parameters data extracted from the principal plane of sky images from the All-Sky Imager. The models use data from a CIMEL CE318 radiometer for training and validation. The deviations between model and reference values are in the range of uncertainties assigned to Aerosol Robotic Network (AERONET) network. [Copyright &y& Elsevier]

Measurements during Saharan dust transport events have been performed at the Andalusian Centre for Environmental Studies (CEAMA) (37.16°N, 3.58°W, 680m a.s.l.), located in the city of Granada (south-eastern Iberian Peninsula). During 2005, as many as 22 dust outbreaks took place over the study area in south-eastern Spain. The arrival of Saharan air masses induced sharp changes in the background aerosol optical depth (AOD) and the Angström exponent during the analysed events. This fact, in addition to a back-trajectory analysis, identified the Saharan dust events. In order to improve knowledge of Saharan dust over the southern Iberian Peninsula, vertical characterization of temporal evolutions has been performed in terms of the backscatter coefficient, aerosol depolarization ratio and colour ratio. Two severe events in July 2005 have been selected for detailed analysis. Both events lasted several days, allowing the characterization of the evolution of the dust layers over our station. The impact of Saharan dust outbreaks has been followed with the Lidar, and their effects at the surface have been determined in the air quality network of the regional government. [Copyright &y& Elsevier]

Surface measurements of optical and physical aerosol properties were made at an urban site, Granada (Spain) (37.18°N, 3.58°W, 680m a.s.l), during winter 2005–2006. Measurements included the aerosol scattering, σ sca, and backscattering coefficients, σ bsca, at three wavelengths (450, 550 and 700nm) measured at low relative humidity (RH<50%) by an integrating nephelometer, the absorption coefficient at 670nm, σ abs, measured with a multi-angle absorption photometer, and aerosol size distribution in the 0.5–20μm aerodynamic diameter range registered by an aerodynamic aerosol sizer (APS-3321, TSI). The hourly average of σ sca (550nm) ranged from 2 to 424Mm−1 with an average value of 84±62Mm−1 (±S.D.). The Angstrom exponent presented an average value of 1.8±0.3, suggesting a large fraction of fine particles at the site, an observation confirmed by aerosol size distribution measurements. The hourly average of σ abs (670nm) ranged from 1.7 to 120.5Mm−1 with an average value of 28±20Mm−1. The results indicate that the aerosol absorption coefficient in Granada was relatively large. The largest σ sca value was associated with air masses that passed over heavily polluted European areas and local stagnation conditions. High absorbing aerosol level was obtained during dust transport from North Africa probably due to the presence of hematite. Based on the measured scattering and absorption coefficients, a very low average value of the single scattering albedo of 0.66±0.11 at 670nm was calculated, suggesting that urban aerosols in this region contain a large fraction of absorbing material. A clear diurnal pattern was observed in scattering and absorption coefficients and particle concentrations with two local maxima occurring in early morning and late evening. This behavior can be explained in terms of local conditions that control the particle sources associated with traffic and upward mixing of the aerosol during the daytime development of a convective boundary layer. Significant reduction in absorption coefficient values has been found during weekends compared to working days, showing a strong impact of local sources on aerosol properties. In contrast to σ abs, the aerosol scattering coefficient obtained during weekends was higher than those obtained on Mondays and Tuesdays. A possible explanation for the large values of σ sca measured during the weekend could be secondary aerosol aging. [Copyright &y& Elsevier]

Abstract: Characterization of mineral aerosol properties in southeastern Spain is important due to its proximity to the African continent that permit studying the Saharan dust just entering European continent before its possible mixing with anthropogenic emissions in Europe. Two Saharan dust events that occurred during 30 August–3 September and on 10 September 1998 were observed at an inland location on the outskirts of Granada in southeastern Spain. Detailed analyses including back trajectories and TOMS aerosol index maps showed transport of Saharan dust from the Sahara desert and North Africa to the study area. The dust episodes were associated with marked increases in aerosol optical depth (δ a) at all wavelengths examined in this study. Thus δ a (500nm) increased from a value of ∼0.2 corresponding to normal conditions up to 0.6 in the first event and up to 0.55 in the second. At the end of these events, the arrival of air masses from the Atlantic caused a sharp decrease in δ a (500nm) that reaches values close to those obtained before the event (∼0.2). The Angström exponent α reached a minimum of 0.36 in the first event and 0.37 in the second. The Angström exponent α and aerosol optical depth values during dust events agree well with those obtained under the same kind of events in AERONET and SKYNET sites, as well as with the results obtained in ACE-2 and ACE-Asia experiments. The aerosol size distributions, retrieved from aerosol optical depth using King''s method, demonstrated how the large size fraction of aerosol associated with Saharan dust dominated during these events. When Saharan dust was present, the retrieved aerosol size distributions were bimodal with a well-defined mode centred at a radius of 0.6μm, and showed an evident increase in the large particles mode with radii in the range 0.4–2μm. The small particle concentration during the two events did not present any marked change, and was similar to those observed on days without Saharan dust. Large particle concentration was higher by a factor of 8 than during normal conditions. [Copyright &y& Elsevier]

Abstract: The radiative characteristics of atmospheric aerosol over a suburban environment on the outskirts of a non-industrialized, medium size city in southeastern Spain (Granada, 37.18°N, 3.58°W, 660m a.m.s.l.) are investigated using 5 years (1994–1998) of continuous spectral photometric measurements in the range 368–778nm. From these measurements, the aerosol optical depth has been determined. In this paper we analyse the aerosol radiative properties derived from the aerosol size distributions, retrieved in a previous study, using Mie theory. The asymmetry factor values are representative of locations with moderate contamination, varying from 0.664 to 0.742 at 500nm. The single scattering albedo evidenced a seasonal pattern, with lower values associated with winter conditions. This parameter varies from 0.928 to 0.966, with mean value of 0.948±0.011 at 500nm. On other hand, the analysed series shows a pronounced change in aerosol radiative characteristic since 1996, which can be associated with urban encroachment on the suburban area. The relationship between g and the aerosol optical depth and its spectral dependence were analysed. Thus, different dependences of g on the Angstrom exponent were encountered for each wavelength analysed, which is of interest for the parametrization of aerosol properties. [Copyright &y& Elsevier]

Presents information on a study conducted which investigated probability density distributions of one-minute values of global irradiance conditioned to air masses. Characteristics of probability density functions; Importance of the knowledge of temporal variability of the solar irradiance to solar energy systems; Analysis of global irradiation values; Frequency distributions of one-minute values.

A growing body of research suggests that pollen suspended in the atmosphere have a major environmental and climatic impact. However, our current knowledge of pollen is rather limited with respect to its extinction capacity, its optical properties and how these vary with atmospheric water content. Understanding their water absorption capacity can improve our understanding of their radiative effects and, thus, improve climate models. In this work, an electrodynamic Paul trap was coupled to a cavity ring down spectroscopy (CRDS) to directly measure the ring down time (τ) of four individual types of pollen particles: Olea , Fraxinus , Populus and Salix exposed to changing relative humidity (RH). Resonant structures in τ values between ∼90 and 45 % RH indicated that pollen was wettable at high RHs. τ was used to calculate light extinction cross-section (σ e x t) at 532 nm as a function of RH. Optical growth factor (f R H ) was evaluated as the ratio between σ e x t (∼ 80 % R H) and σ e x t (d r y). From f R H , the semi-empirical single hygroscopicity parameter (κ e m p ) was found to be 0.038–0.058 for the four pollen types. Under controllable treatment of the water content and an adequate selection of complex refractive index (m) , CRDS- σ e x t data was fitted to theoretical σ e x t from Mie theory. The reasonable agreement achieved allowed for gaining knowledge about the m and how particle size shrugged during dehydration. As a result, a climate-lowering effect of Olea pollen particles, which contain a fraction of scattered aerosol, should be considered in the models. • Cavity ring down time measurements were measured for single pollen particles for the first time. • The dependency on relative humidity was calculated for extinction cross sections. • Refractive index was retrieved from the fit with Mie theory. SYNOPSIS: This study provides optical properties of pollen (complex refractive index) and their dependence on water content, which has environmental relevance from the point of view of radiative effects. [ABSTRACT FROM AUTHOR]

During the 2017 record-breaking burning season in Canada/United States, intense wild fires raged during the first week of September in the Pacific northwestern region (British Columbia, Alberta, Washington, Oregon, Idaho, Montana and northern California) burning mostly temperate coniferous forests. The heavy loads of smoke particles emitted in the atmosphere reached the Iberian Peninsula (IP) a few days later on 7 and 8 September. Satellite imagery allows to identify two main smoke clouds emitted during two different periods that were injected and transported in the atmosphere at several altitude levels. Columnar properties on 7 and 8 September at two Aerosol Robotic Network (AERONET) mid-altitude, background sites in northern and southern Spain are: aerosol optical depth (AOD) at 440 nm up to 0.62, Ångström exponent of 1.6–1.7, large dominance of small particles (fine mode fraction >0.88), low absorption AOD at 440 nm (<0.008) and large single scattering albedo at 440 nm (>0.98). Profiles from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) show the presence of smoke particles in the stratosphere during the transport, whereas the smoke is only observed in the troposphere at its arrival over the IP. Portuguese and Spanish ground lidar stations from the European Aerosol Research Lidar Network/Aerosols, Clouds, and Trace gases Research InfraStructure Network (EARLINET/ACTRIS) and the Micro-Pulse Lidar NETwork (MPLNET) reveal smoke plumes with different properties: particle depolarization ratio and color ratio, respectively, of 0.05 and 2.5 in the mid troposphere (5–9 km) and of 0.10 and 3.0 in the upper troposphere (10–13 km). In the mid troposphere the particle depolarization ratio does not seem time-dependent during the transport whereas the color ratio seems to increase (larger particles sediment first). To analyze the horizontal and vertical transport of the smoke from its origin to the IP, particle dispersion modelling is performed with the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) parameterized with satellite-derived biomass burning emission estimates from the Global Fire Assimilation System (GFAS) of the Copernicus Atmosphere Monitoring Service (CAMS). Three compounds are simulated: carbon monoxide, black carbon and organic carbon. The results show that the first smoke plume which travels slowly reaches rapidly (~1 day) the upper troposphere and lower stratosphere (UTLS) but also shows evidence of large scale horizontal dispersion, while the second plume, entrained by strong subtropical jets, reaches the upper troposphere much slower (~2.5 days). Observations and dispersion modelling all together suggest that particle depolarization properties are enhanced during their vertical transport from the mid to the upper troposphere. • Long-range transport of a smoke plume from northern America to Europe • Time-space monitoring with ground and space-borne lidars of a smoke plume • Injection of smoke particles up to the upper troposphere (<13 km) • Dispersion model parameterization with satellite-based biomass burning estimates • Possible rationales for the smoke absorption and depolarization properties observed [ABSTRACT FROM AUTHOR]

This work deals with the set up and optimization of a commercial multiwavelength polarized imaging nephelometer (PI-Neph, Airphoton PIN100) designed to measure F 11 (phase function) and –F 12 /F 11 (polarized phase function) from ambient aerosol samples. Such measurements are critical for the success of upcoming satellite missions based on polarimetry measurements because they will support and validate retrieval techniques. The main novelty of the instrument with respect to previous versions consists of using only one beam instead of a mirror system to fold it, avoiding internal reflections of light and loss of energy within the laser beam. The instrument also includes the automatization of the imaging technique that makes possible continuous measurements in near real time of the aerosol phase functions at different states of linear polarization directly from ambient air. Laser emits at three different wavelengths (405, 515 and 660 nm) and the beam goes through a wire grid polarizer for linearly polarizing the light, followed by two liquid crystal retarders that control the state of linear polarization. The detector is a CMOS camera perpendicular to the beam which allows to obtain final phase functions in the range 5°–175° (losses of some angles by physical limitations and stray light). The calibration of the instrument is discussed and includes geometric calibration (to account for different light paths to the camera) plus absolute calibration (to obtain physical units). Temporal stability of calibrations is observed, and different data quality tests are presented in order to obtain reliable values of F 11 and –F 12 /F 11. For an automatic operation of the instrument that permits real time phase matrix measurements, a data quality check algorithm that avoids non-physical measurements and filters outliers has been developed. Validation of the scattering matrix elements based on monodisperse aerosol measurements is also done with polystyrene latex spheres (PSL), showing good agreement with Mie theory. Finally, first results of the instrument operating at the University of Granada (UGR) station from the Andalusian Global ObseRvatory of the Atmosphere (AGORA) since April 2022 are presented. Very good agreements of the integrated scattering coefficients with an integrating nephelometer (TSI, model 3563) were obtained with high correlation coefficients for the three wavelengths (R2 > 0.81). The calculated root-mean-square error (RMSE) reveals that the performance of the PI-Neph in the measurement of the scattering coefficient is better in the 660 nm and 515 nm wavelengths than in the 405 nm one, although differences between datasets are still low. The observed differences in phase functions and especially polarized phase functions (both in shape and spectral differences) under changing atmospheric scenarios (Saharan dust, pollution and background aerosol conditions) indicated that these variables are sensitive and reliable to classify the type of ambient aerosol. Particularly, the combined measurements of F 11 and –F 12 /F 11 shows a unique potential of the PI-Neph for aerosol typology. • Optimization of multiwavelength Polarized Imaging Nephelometer (PI-Neph). • Phase matrix elements of ambient aerosols in support of satellite measurements. • Validation of PI-Neph measurements. • Aerosol phase function and polarized phase function for different aerosol types. [ABSTRACT FROM AUTHOR]

The study of the interaction of light with matter upon changing environmental conditions requires new platforms that provide accurate and reliable measurements. One suitable technique for studying such interaction uses electrodynamic traps to levitate micro or nanoparticles in combination with an optical interrogation technique, but improvements and new developments that complement spectroscopic information are necessary. Here, we use a Paul Electrodynamic Trap (PET) coupled to a Double-Cavity Ring Down Spectroscopy (D-CRDS) to measure the extinction cross section of single levitated particles at two different wavelengths (405 and 532 nm). The level of control achieved over the motion and stability is such that the particle can be consecutively placed at the central maximum of two independent TEM 00 Gaussian modes of the ring-down cavities. Therefore, we can directly measure the dynamic change of the extinction cross section of a single particle at two different wavelengths. The combination of simulations using Mie theory and experiments demonstrates the potential of this robust and versatile setup applied to 1,2,6-hexanetriol particles. Unlike standard methods, our system provides crucial information of drastic and reversible change in the extinction cross-section of a sodium chloride particle in efflorescence and deliquescence points, indicating changes in solute mass, charge, refractive index, sphericity and size during the dehydration and hydration processes. [Display omitted] • Double Cavity ring down time data were measured for the same single aerosol particle for the first time. • The dependency on relative humidity was calculated for extinction cross sections. • Refractive index was retrieved from the fit with Mie theory. [ABSTRACT FROM AUTHOR]

This study synthesizes for the first time results from simultaneous aerosol measurements performed at seven diverse locations distributed all over the Spanish geography. The observations were carried out during two field campaigns in 2012–2013, one-month each and during different seasons. These field campaigns were performed in the framework of the Spanish Network of DMAs (REDMAAS) activities. Measurement sites were grouped as polluted sites (urban background) and clean sites (rural background and high-altitude sites). Seasonal differences were more important at polluted sites, mainly related to meteorology and aerosol sources. Higher total particle concentrations were found during the cold period, driven mainly by Aitken-mode particles (traffic-related aerosol particles). In clean sites, particle concentrations were higher during the warm period. Mild meteorological conditions in combination with the absence of local sources during the cold period make atmospheric nucleation an important contributor to ultrafine particles. These results are reflected in aerosol dynamical processes. Ultrafine particle bursts were frequent in both periods at the clean sites and in the warm period at most polluted sites. Shrinkages processes were identified at three sites (two polluted and one clean site) during the warm period. Meteorology (wind speed and solar radiation) and a highly-volatile aerosol (formed from atmospheric nucleation or traffic emissions) explain this behaviour. Ultrafine particles exhibited a different behaviour at inland and coastal sites. The highest total particle concentrations were observed at coastal sites during the warm period. At these sites, the smallest particle modal diameters and the highest variations of particle number size distributions in the smaller particle size range were also found, particularly in the warm period. This may be the result of the high diffusion conditions and mixing of different air masses (clean and polluted) caused by sea-land breezes. Our findings can be explained by the local and regional characteristics of each site, such as meteorology and aerosol sources (types, proximity …) and the influence of meteorology on atmospheric transformation processes. [ABSTRACT FROM AUTHOR]

Wind-dispersed pollen grains emitted from vegetation are directly injected into the atmosphere being an important source of natural aerosols globally. These coarse particles of pollen can rupture into smaller particles, known as subpollen particles (SPPs), that may act as cloud condensation nuclei (CCN) and affect the climate. In this study, we characterize and investigate the ability of SPPs of 10 Mediterranean-climate pollen types to activate as CCN. A continuous flow CCN counter (CCNC) was used to measure the activation of size-selected (80, 100 and 200 nm dry mobility diameter) particles at different supersaturations (SS). Hygroscopicity parameter (κ) for each SPP type and size has been calculated using κ-Köhler theory. Organic chemical speciation and protein content has been determined to further characterize pollen solutions. Furthermore, the surface activity of SPPs has also been investigated by using pendant drop tensiometry. All studied SPP samples show critical supersaturation (SS Crit) values that are atmospherically relevant SS conditions. Hygroscopicity κ values are in the range characteristic of organic compounds (0.1–0.3). We found that organic speciation and protein content vary substantially among pollen types, with saccharides and fatty acids being the only organic compounds found in all pollen types. A clear relationship between SPP activation and its organic composition was not observed. This study also reveals that all SPPs investigated reduce the surface tension of water at high concentrations but at diluted concentrations (such as those of activation in the CCNC), the water surface tension value is a good approximation in Köhler theory. Overall, this analysis points out that pollen particles might be an important source of CCN in the atmosphere and should be considered in aerosol-cloud interactions processes. [Display omitted] • Subpollen particles (SPPs) show κ values in the 0.1–0.3 range. • SPPs activate as CCN at atmospheric supersaturation conditions. • Saccharides and fatty acids are organic compounds found in all pollen types. • The droplet surface tension reduction is observed at high concentration of SPPs. • Reduction of surface tension does not show a relevant effect on SPP activation. [ABSTRACT FROM AUTHOR]

In this study, aerosol light-absorption measurements obtained at three sites during a winter campaign were used to analyse and identify the major sources of Black Carbon (BC) particles in and around the Alhambra monument, a UNESCO World Heritage Site that receives over 2 million visitors per year. The Conditional Bivariate Probability Function and the Aethalometer model were employed to identify the main sources of BC particles and to estimate the contributions of biomass burning and fossil fuel emissions to the total Equivalent Black Carbon (EBC) concentrations over the monumental complex. Unexpected high levels of EBC were found at the Alhambra, comparable to those measured in relatively polluted European urban areas during winter. EBC concentrations above 3.0 μg/m 3 , which are associated with unacceptable levels of soiling and negative public reactions, were observed at Alhambra monument on 13 days from 12 October 2015 to 29 February 2016, which can pose a risk to its long-term conservation and may cause negative social and economic impacts. It was found that road traffic emissions from the nearby urban area and access road to the Alhambra were the main sources of BC particles over the monument. However, biomass burning emissions were found to have very small impact on EBC concentrations at the Alhambra. The highest EBC concentrations were observed during an extended stagnant episode associated with persistent high-pressure systems, reflecting the large impact that can have these synoptic conditions on BC over the Alhambra. [ABSTRACT FROM AUTHOR]

This work focuses on the analysis of columnar aerosol properties in the complex geophysical tropical region of South America within 10–20° South and 50–70° West. The region is quite varied and encompasses a significant part of Amazonia (lowlands) as well as high mountains in the Andes (highlands,∼4000 m a.s.l.). Several AERONET stations were included to study the aerosol optical characteristics of the lowlands (Rio Branco, Ji Parana and Cuiaba in Brazil and Santa Cruz in Bolivia) and the highlands (La Paz, Bolivia) during the 2000–2014 period. Biomass-burning is by far the most important source of aerosol in the lowlands, particularly during the dry season (August–October). Multi-annual variability was investigated and showed very strong burning activity in 2005, 2006, 2007 and 2010. This resulted in smoke characterized by correspondingly strong, above-average AODs (aerosol optical depths) and homogeneous single scattering albedo (SSA) across all the stations (∼0.93). For other years, however, SSA differences arise between the northern stations (Rio Branco and Ji Parana) with SSAs of ∼0.95 and the southern stations (Cuiaba and Santa Cruz) with lower SSAs of ∼0.85. Such differences are explained by the different types of vegetation burned in the two different regions. In the highlands, however, the transport of biomass burning smoke is found to be sporadic in nature. This sporadicity results in highly variable indicators of aerosol load and type (Angstrom exponent and fine mode fraction) with moderately significant increases in both. Regional dust and local pollution are the background aerosol in this highland region, whose elevation places it close to the free troposphere. Transported smoke particles were generally found to be more optical absorbing than in the lowlands: the hypothesis to explain this is the significantly higher amount of water vapor in Amazonia relative to the high mountain areas. The air-mass transport to La Paz was investigated using the HYSPLIT air-concentration five-days back trajectories. Two different patterns were clearly differentiated: westerly winds from the Pacific that clean the atmosphere and easterly winds favoring the transport of particles from Amazonia. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Knowledge of the scattering enhancement factor, f (RH), is important for an accurate description of direct aerosol radiative forcing. This factor is defined as the ratio between the scattering coefficient at enhanced relative humidity, RH, to a reference (dry) scattering coefficient. Here, we review the different experimental designs used to measure the scattering coefficient at dry and humidified conditions as well as the procedures followed to analyze the measurements. Several empirical parameterizations for the relationship between f (RH) and RH have been proposed in the literature. These parameterizations have been reviewed and tested using experimental data representative of different hygroscopic growth behavior and a new parameterization is presented. The potential sources of error in f (RH) are discussed. A Monte Carlo method is used to investigate the overall measurement uncertainty, which is found to be around 20–40% for moderately hygroscopic aerosols. The main factors contributing to this uncertainty are the uncertainty in RH measurement, the dry reference state and the nephelometer uncertainty. A literature survey of nephelometry-based f (RH) measurements is presented as a function of aerosol type. In general, the highest f( RH) values were measured in clean marine environments, with pollution having a major influence on f( RH). Dust aerosol tended to have the lowest reported hygroscopicity of any of the aerosol types studied. Major open questions and suggestions for future research priorities are outlined. [ABSTRACT FROM AUTHOR]

A set of 6500 angular scattering function data have been obtained at various locations of the world: Vienna (Austria), Kyoto (Japan), Granada (Spain) and Palencia (Spain). The aerosols in these locations were considerably different, ranging from continental, urban, maritime, to desert dust. The volume scattering function has been measured between 5° and 175°, the values for 0–5° and 175–180° have been obtained by extrapolation of the shape of the curve, thus the whole range of scattering angles was available for calculating the backscattered fraction and the asymmetry parameter of the aerosol. The majority of the data points suggest an unanimous relation between backscattering and asymmetry parameter. The location where sampling took place and the type of aerosol seems to be of minor importance. These data have been compared with results of calculations for spherical or ellipsoidal particles having a lognormal monomodal size distribution of various sizes as well as several approximations for the relationship asymmetry vs backscattering available from the literature. With one exception it appears that an unanimous relation, fairly independent of location and type of aerosol, has been found between asymmetry parameters and backscattering ratio. The assumption of spherical particles seems to be a good assumption. Only for aerosols dominated by coarse mode particles the data points fall outside of the general trend, but again Mie calculations for spherical particles explain the behaviour. [ABSTRACT FROM AUTHOR]