Atmospheric Turbidity Research Articles

A Fresh Approach to the Study of Atmosphere Turbidity

The problem of assessment of atmospheric turbidity caused by aerosol particles, viz., dust, smoke, haze, and other atmospheric pollutants, apart from the effect of variable water vapour content of the atmosphere, has been studied afresh. The basic concept underlying Linke's turbidity factor, T has been found to be theoretically sound, although its quantitative formulation suffers from one major defect, viz, its 'virtual variation' with air mass. This error has been traced to defective formulation of the quantitative expression for T. A 'Rational turbidity factor', Tr, has been proposed which is likely to overcome the limitations of Linke's turbidity factor, T. A nomogram has been development for quick evaluation of Tr, and the effect of altitude has also been considered.

Estimation of the error of lidar determination of the transparency of low-turbidity atmosphere

Considered is the method of determination of atmospheric turbidity using weak lidar signals when the problem is mathematically incorrect due to the presence of the background noise. An accuracy of the method can be increased by means of using the procedure of effective averaging and linear approximation of the transmission in the case of the low attenuation coefficient.

Design of a device for sky light polarization measurements.

Sky polarization patterns can be used both as indicators of atmospheric turbidity and as a sun compass for navigation. The objective of this study is to improve the precision of sky light polarization measurements by optimal design of the device used. The central part of the system is composed of a Charge Coupled Device (CCD) camera; a fish-eye lens and a linear polarizer. Algorithms for estimating parameters of the polarized light based on three images are derived and the optimal alignments of the polarizer are analyzed. The least-squares estimation is introduced for sky light polarization pattern measurement. The polarization patterns of sky light are obtained using the designed system and they follow almost the same patterns of the single-scattering Rayleigh model. Deviations of polarization angles between observation and the theory are analyzed. The largest deviations occur near the sun and anti-sun directions. Ninety percent of the deviations are less than 5° and 40% percent of them are less than 1°. The deviations decrease evidently as the degree of polarization increases. It also shows that the polarization pattern of the cloudy sky is almost identical as in the blue sky.

Quantitative analysis of night skyglow amplification under cloudy conditions

The radiance produced by artificial light is a major source of nighttime over-illumination. It can, however, be treated experimentally using ground-based and satellite data. These two types of data complement each other and together have a high information content. For instance, the satellite data enable upward light emissions to be normalized, and this in turn allows skyglow levels at the ground to be modelled under cloudy or overcast conditions. Excessive night lighting imposes an unacceptable burden on nature, humans and professional astronomy. For this reason, there is a pressing need to determine the total amount of downwelling diffuse radiation. Undoubtedly, cloudy periods can cause a significant increase in skyglow as a result of amplification owing to diffuse reflection from clouds. While it is recognized that the amplification factor (AF) varies with cloud cover, the effects of different types of clouds, of atmospheric turbidity and of the geometrical relationships between the positions of an individual observer, the cloud layer, and the light source are in general poorly known. In this paper the AF is quantitatively analysed considering different aerosol optical depths (AODs), urban layout sizes and cloud types with specific albedos and altitudes. The computational results show that the AF peaks near the edges of a city rather than at its centre. In addition, the AF appears to be a decreasing function of AOD, which is particularly important when modelling the skyglow in regions with apparent temporal or seasonal variability of atmospheric turbidity. The findings in this paper will be useful to those designing engineering applications or modelling light pollution, as well as to astronomers and environmental scientists who aim to predict the amplification of skyglow caused by clouds. In addition, the semi-analytical formulae can be used to estimate the AF levels, especially in densely populated metropolitan regions for which detailed computations may be CPU-intensive. These new results are of theoretical and experimental significance as they will motivate experimentalists to collect data from various regions to build an overall picture of the AF, and will encourage modellers to test the consistency with theoretical predictions.

Numerical simulation of solar parabolic trough collector performance in the Algeria Saharan region

In order to determine the optical and thermal performance of a solar parabolic trough collector under the climate conditions of Algerian Sahara, a computer program based on one dimensional implicit finite difference method with energy balance approach has been developed. The absorber pipe, glass envelope and fluid were divided into several segments and the partial derivation in the differential equations was replaced by the backward finite difference terms in each segment. Two fluids were considered, liquid water and TherminolVP-1™ synthetic oil. Furthermore, the intensity of the direct solar radiation was estimated by monthly average values of the atmospheric Linke turbidity factor for different tracking systems. According to the simulation findings, the one axis polar East–West and horizontal East–West tracking systems were most desirable for a parabolic trough collector throughout the whole year. In addition, it is found that the thermal efficiency was about 69.73–72.24%, which decreases with the high synthetic oil fluid temperatures and increases in the lower water temperature by 2%.

The signal of aerosol‐induced changes in sunshine duration records: A review of the evidence

AbstractAerosols play a significant yet complex and central role in the Earth's radiation budget, and knowledge of long‐term changes in the atmospheric turbidity induced by aerosols is therefore fundamental for a better understanding of climate change. However, there is little available information on changes in aerosol concentration in the atmosphere, especially prior to the 1980s. The present paper reviews publications reporting the suitability of sunshine duration records with regard to detecting changes in atmospheric aerosols. Some of the studies reviewed propose methods for estimating aerosol‐related magnitudes, such as turbidity, from sunshine deficit at approximately sunrise and sunset, when the impact of aerosols on the solar beam is more easily observed. In addition, there is abundant evidence that one cause of the decadal changes observed in sunshine duration records involves variations in atmospheric aerosol loading. Possible directions for future research are also suggested: in particular, detailed studies of the burn (not only its length but also its width) registered by means of Campbell‐Stokes sunshine recorders may provide a way of creating time series of atmospheric aerosol loading metrics dating back to over 120 years from the present.

Variations of aerosol optical depth and Angstrom parameters at a suburban location in Iran during 2009–2010

Solar irradiance is attenuated spectrally when passing through the earth’s atmosphere and it is strongly dependent on sky conditions, cleanliness of the atmosphere, composition of aerosols and gaseous constituents. In this paper, aerosol optical properties including aerosol optical depth (AOD), Angstrom exponent (α) and Angstrom turbidity coefficient (β) have been investigated during December 2009 to October 2010, in a suburban area of Zanjan (36°N, 43°E, 1700 m), in the north–west of Iran, using meteorological and sun photometric data. Results show that turbidity varies on all time scales, from the seasonal to hourly, because of changes in the atmospheric meteorological parameters. The values of α range from near zero to 1.67. The diurnal variation of AOD in Zanjan is about 15%. The diurnal variability of AOD, showed a similar variation pattern in spring (including March, April, May) and winter (December, January, February) and had a different variation pattern in summer (June, July, August) and autumn (September and October). During February, spring and early summer winds transport continental aerosols mostly from the Iraq (dust events) and cause the increase of beta and turbidity of atmosphere of Zanjan.

Atmospheric Turbidity Forecasting using Side-by-side ANFIS

In a context of sustainable development, enthusiasm for CSP technologies is increasing. In addition, the CSPIMP (Concentrated Solar Power efficiency IMProvement) European project has been recently initiated to achieve a better competitiveness of the CSP plants. Its main objective is to develop a new procedure to improve the steam turbine start up cycles, maintenance activities and advanced plant control schemes. A challenge in the project is to forecast the solar resource with the aim of improving the management of CSP plants. A key parameter when trying to estimate or forecast solar radiation is atmospheric turbidity. Indeed, the Direct Normal Irradiance (DNI) under clear sky conditions can be expressed as a function of extraterrestrial irradiation, altitude and atmospheric turbidity. So, this paper focuses on forecasting atmospheric turbidity at different time horizons (up to 3hours) using side-by-side Adaptive Network-based Fuzzy Inference Systems (ANFIS). First, a Multi-Resolution Analysis (MRA) based on the discrete wavelet transform allowed clear sky DNI values to be extracted from the NREL database. In addition, a Principal Component Analysis (PCA) has been considered in order to develop the forecasting model using uncorrelated input variables and reduce its complexity (and, as a consequence, computation time). Finally, the results we obtained about atmospheric turbidity forecasting are satisfactory and validate the proposed approach.

Remote Sensing and GIS in planning photovoltaic potential of urban areas

The last guidelines approved by Italian government to financially support the solar Photovoltaic (PV) Energy production development include specific indications for more advantageously funding installations exploiting roofs/covers surfaces mainly located in urban or industrial areas. Since the 3D heterogeneity, albedo, atmospheric turbidity and casting shadows significantly influence here the local solar irradiance, the implemented methodology allowed us to suitably account for these distributed factors by means active (LIDAR) and passive satellite/airborne remote sensing techniques and advanced GIS modelling tools in order to support more realistic estimates of PV potential at roofs level in urban areas.

Intra-Day DNI Forecasting Under Clear Sky Conditions Using ANFIS

Abstract The present paper deals with the developement of a new intra-day Direct Normal Irradiance (DNI) forecasting methodology, under clear sky conditions. Indeed, one challenge of the CSPIMP (Concentrated Solar Power plant efficiency IMProvement) research project is to forecast the sun's resource accurately and design efficient plant control approaches. First, a quick review of the different formulations available for the atmospheric turbidity coefficient (from which DNI can be calculated) is performed. The data selection and filtering process is then described. Finally, the new forecasting approaches are compared to persistent and autoregressive models. The most efficient model presented here is based on side-by-side Adaptive Network-based Fuzzy Inference Systems (ANFIS). The selected configuration achieves very good results and validates the proposed forecasting methodology.

Evaluation of four MERIS atmospheric correction algorithms in Lake Kasumigaura, Japan

Accurate atmospheric correction for turbid inland waters remains a significant challenge. Several atmospheric correction algorithms have been proposed to address this issue, but their performance is unclear in regard to Asian lakes, some of which have extremely high turbidity and different inherent optical properties from lakes in other continents. Here, four existing atmospheric correction algorithms were tested in Lake Kasumigaura, Japan (an extremely turbid inland lake), using in situ water-leaving reflectance and concurrently acquired medium resolution imaging spectrometer (MERIS) images. The four algorithms are (1) GWI (the standard Gordon and Wang algorithm with an iterative process and a bio-optical model) (2) MUMM (Management Unit of the North Sea Mathematical Models); (3) SCAPE-M (Self-Contained Atmospheric Parameters Estimation for MERIS Data) and (4) C2WP (Case-2 Water Processor). The results show that all four atmospheric correction algorithms have limitations in Lake Kasumigaura, even though SCAPE-M and MUMM gave acceptable accuracy for atmospheric correction in several cases (relative errors less than 30% for the 2006 and 2008 images). The poor performance occurred because the conditions in Lake Kasumigaura (i.e. the atmospheric state and/or turbidity) did not always meet the assumptions in each atmospheric correction algorithm (e.g. in 2010, the relative errors ranged from 42% to 83%). These results indicate that further improvements are necessary to address the issue of atmospheric correction for turbid inland waters such as Lake Kasumigaura, Japan.

Impact of meteorological parameters on relation between aerosol optical indices and air pollution in a sub-urban area

Aerosol optical depth (AOD) provides a useful characterization of the total absorption and scattering effect of particles in direct or scattered sunlight, and can be derived from sun spectra measured directly by sun photometers. In this paper, atmospheric optical properties (e.g. AOD440–1020nm, α and β, the coefficients in Angstrom formula) and meteorological conditions are presented for: summer (July–August–September) and winter (December–January–February–March) of 2009–2010 over Zanjan (36.41° N, 48.29° E) in northwestern Iran.The diurnal variation of AOD in Zanjan is approximately 15%. An exponential dependence of α on AOD in winter indicates that dust aerosols are major contributions of atmospheric turbidity in this region. AOD regressed against PM10 to establish prediction models. The role of three meteorological parameters on the correlation of AOD and PM10 are analyzed. Results show that there is a high correlation between AOD440 and PM10 in wintertime, and β is a better indicator of air quality in winter than in summer for the study region considered here. Hourly analysis shows that this correlation is highest in the afternoon when the atmospheric mixed layer is at its highest thickness. A similar behavior for AOD–PM10 and a correlation between optical properties with NO2 and PM10 are detected. A sensitivity study was designed to quantify the role of meteorological properties, such as relative humidity, wind speed, and temperature, on the correlation between AOD and PM10 concentration.

An analysis of the extinction of direct solar radiation on Mt. Kasprowy Wierch, Poland

The study describes the extinction of direct solar radiation in a high mountainous region, as represented by the example of Mount Kasprowy Wierch (in the Tatra Mountains, Poland), in the period of 1964–2003. The location is specific due to its high elevation (1991ma.s.l.) and lack of significant local sources of industrial pollution. The data used for this study had been made available by the Institute of Meteorology and Water Management (Poland).The extinction of solar radiation was expressed by means of Linke's turbidity factor (TL2), the atmospheric transparency coefficient (p2) and Ångström's turbidity coefficient (βL2). Changes in individual optical characteristics of the atmosphere were presented in diurnal and annual courses and in distinguished long-term periods. In a diurnal course, the smallest extinction of solar radiation in the studied period occurred before midday (TL2=2.17), whereas in the afternoon its value increased (TL2=2.40). In an annual course, not unlike in a number of other locations where such studies had been carried out, the atmosphere was the most transparent to solar radiation in the winter (TL2=1.96) and the least in the summer (TL2=2.86). In a multi-annual course, divided into two long-term sub-periods, less extinction of solar radiation occurred in the second of these (1994–2003).Several factors, both natural and anthropogenic, contributed to the improvement in the optical state of the atmosphere in the second sub-period. A decrease in volcanic activity observed at that time is one significant natural factor, whereas in the case of the anthropogenic factors, a substantial reduction of atmospheric emissions resulting from social and political transformations in Central and Eastern Europe is an important aspect. These transformations had triggered considerable economic changes, with reduced emissions being one of the outcomes.The extinction of solar radiation was also juxtaposed with the prevailing air masses. The smallest atmospheric turbidity was found in arctic air masses (TL2=2.07), whereas the greatest turbidity was characteristic of tropical air masses (TL2=2.69).

Fugitive particulate emission factors for dry fly ash disposal

Dry fly ash disposal involves dropping ash from a truck and the movement of a heavy grader or similar vehicle across the ash surface. These operations are known to produce fugitive particulate emissions that are not readily quantifiable using standard emission measurement techniques. However, there are numerous situations--such as applying for a source air permit--that require these emissions be quantified. Engineers traditionally use emission factors (EFs) derived from measurements of related processes to estimate fly ash disposal emissions. This study near a dry fly ash disposal site using state-of-the-art particulate monitoring equipment examines for the first time fugitive emissions specific to fly ash handling at an active disposal site. The study measured hourly airborne mass concentrations for particles smaller than 2.5 μm (PM2.5) and 10 μm (PM10) along with meteorological conditions and atmospheric turbidity at high temporal resolution to characterize and quantify fugitive fly ash emissions. Fugitive fly ash transport and dispersion were computed using the on-site meteorological data and a regulatory air pollutant dispersion model (AERMOD). Model outputs coupled with ambient measurements yielded fugitive fly ash EFs that averaged 96 g Mg−1 (of ash processed) for the PMc fraction (=PM10 - PM2.5) and 18 g Mg−1 for PM2.5. Median EFs were much lower due to the strongly skewed shape of the derived EF distributions. Fugitive EFs from nearby unpaved roads were also characterized. Our primary finding is that EFs for dry fly ash disposal are considerably less than EFs derived using US Environmental Protection Agency AP-42 Emissions Handbook formulations for generic aggregate materials. This appears to be due to a large difference (a factor of 10+) between fugitive vehicular EFs estimated using the AP-42 formulation for vehicles driving on industrial roads (in this case, heavy slow-moving grading equipment) and EFs derived by the current study. Implications Fugitive fly ash emission factors (EFs) derived by this study contribute to the small existing knowledge base for a type of pollutant that will become increasingly important as ambient particulate standards become tighter. In areas that are not in attainment with standards, realistic EFs can be used for compliance modeling and can help identify which classes of sources are best targeted to achieve desired air quality levels. In addition, understanding the natural variability in fugitive fly ash emissions can suggest methods that are most likely to be successful in controlling fugitive emissions related to dry fly ash storage.

Posidonia oceanica genetic and biometry mapping through high-resolution satellite spectral vegetation indices and sea-truth calibration

In the framework of Posidonia oceanica (PO) preservation activities, a small-scale restoration pilot project was implemented in 2005 at a Santa Marinella site to replace the loss of this important species of seagrass in this zone of the central Tyrrhenian coast via an innovative transplantation approach. In this context, taking into account the recent advances in the fields of high-resolution (HR) satellite/airborne remote-sensing and genetics laboratory analysis techniques, we propose this integrated methodology for monitoring changes in transplanted meadows in regard to perspective to provide support in the assessment of the entire local PO and seagrass population dynamic. According to specific information requirements in terms of radiometric and spectral/spatial resolution, the multispectral data currently available from the QuickBird polar satellite’s four-band (red, green, blue visible and near-infrared) HR sensor were exploited for methodology implementation using a practical ‘image-based’ approach to account for atmospheric and water column turbidity typical of this mid-coastal Mediterranean region. First, the extents and types of seagrass cover were suitably mapped, and then also the distributions of specific vegetation parameters related to PO dynamics and health were assessed by exploiting the remotely sensed satellite-derived radiance signals and point sea-truth calibration measurements of the bio-genetic parameters. In particular, we implemented maps of leaf area index, genetic similarity, and density Giraud indices corresponding to distributions of PO patches using multivariate and data-mining models (artificial neural network) based on appropriately preprocessed radiometric and auxiliary (bathymetry) input variables.

Estimation of atmospheric turbidity over Ghardaïa city

The atmospheric turbidity expresses the attenuation of the solar radiation that reaches the Earth's surface under cloudless sky and describes the optical thickness of the atmosphere. We investigate the atmospheric turbidity over Ghardaïa city using two turbidity parameters, the Linke turbidity factor and the Angström turbidity coefficient. Their values and temporal variation are obtained from data recorded between 2004 and 2008 at Ghardaïa. The results show that both parameters have the same trend along the year. They reach their maximum around summer months and their minimum around winter months. The monthly average value varies between 1.3 and 5.6 for the Linke turbidity factor and between 0.02 and 0.19 for the Angström turbidity coefficient. We find that 39.8% of the Linke turbidity factor values are less than 3, 47.5% are between 3 and 5 and only 12.7% are greater than 5. For the Angström turbidity coefficient, 9.4% of the values are less than 0.02, 75.4% are between 0.02 and 0.15 and 15.2% exceed 0.15.

Retrieval of aerosol optical and microphysical characteristics according to data from ground-based spectral measurements of direct and diffuse solar radiation. Part 2. Algorithm testing

We present the results of the study of sensitivity of our algorithm for retrieving the columnar aerosol optical and microphysical characteristics to measurement errors. The algorithm testing against data from field measurements under conditions of both increased and moderate aerosol turbidity of the clear sky atmosphere is discussed. We present the average values of the aerosol optical and microphysical characteristics retrieved according to data from photometric measurements at the AERONET station in Tomsk during 2004–2009 for situations when the aerosol optical depth in the spectral channel of 440 nm did not exceed 0.4.

Atmospheric turbidity determined by the annual cycle of the aerosol optical depth over north-center Spain from ground (AERONET) and satellite (MODIS)

The present study focuses on the characterization of aerosol seasonal variability over the northern continental region of the Iberian Peninsula based on remotely sensed aerosol optical properties, and in particular the aerosol optical depth (AOD) and Ångström exponent (Alpha) parameters. For this region, a representative annual cycle of these parameters was built based on data from the AERONET-RIMA station of Palencia (Spain, 42N, 4.5W) for the period 2003–2011. The results also examine in details the interannual variability during the whole period. The ability of satellite to reproduce the seasonal patterns and anomalies, is investigated using the MODIS (Moderate Resolution Imaging Radiometer) for the same period. MODIS instantaneous fields are validated against ground-based sunphotometer data, and the differences between monthly values are estimated. The site of Palencia is characterized by a daily AOD (440 nm) of 0.15 ± 0.10 and Alpha (440–870 nm) of 1.29 ± 0.35 on average, thus presenting values typical of a clean continental background. The seasonal pattern corresponds to mid-high turbidity values of the AOD during a period starting in mid-spring to the end of the summer (max 0.19), and a lower AOD during fall and winter months (min 0.09). When using MODIS data, the overall results for Palencia give a higher (by ∼25%) AOD (470 nm) with 0.19 ± 0.15 and a much lower (by ∼50%) Alpha (470–660 nm) of 0.70 ± 0.20. These numbers reflect substantial differences, with overestimations of the monthly means that can be almost double those of AERONET in the summer months. However MODIS satisfactorily reproduces the increase–decrease cycle in the AOD. These large differences tend to be more attributed to the aerosol models used in the MODIS algorithm rather than to the sampling difference between ground and satellite in this season. Despite the poor sampling in winter and the small AOD (<0.1) observed over the area, the best agreement between satellite and ground is found during this period. The seasonal pattern of the Ångström exponent derived from MODIS was found to be very different from that of AERONET, the former showing apparently no consistency with the latter. Given the aforementioned values and the fact that the AERONET Alpha value for 470–660 nm is 1.41 ± 0.37 (wavelengths used in the comparison with MODIS), we can conclude that the Alpha derived from MODIS is not representative of the aerosol type characterizing this region of the globe.

Estimates of the Linke turbidity factor over Zimbabwe using ground-measured clear-sky global solar radiation and sunshine records based on a modified ESRA clear-sky model approach

This paper describes a procedure that can be used to calculate values for Linke atmospheric turbidity factors at air mass 2 (TL2) over Zimbabwe. Ground measured daily global solar radiation on clear days over 3years is used to evaluate TL2 for those stations that measure global radiation. The evaluation makes use of the clear-sky model of the European Solar Radiation Atlas (ESRA) combined with a diffuse transmittance model developed in the study. For those stations that do not measure global radiation but have sunshine duration records, global radiation values are generated through Angstrom type regression coefficients between the clearness index and relative sunshine duration. The TL2 values that are generated from the ESRA model are higher than those obtained from the study model (root mean square error (RMSE) up to 1.0 Turbidity Units). When compared to TL2 values from this study, the worldwide database SoDA, give significantly higher TL2 values (RMSE up to 2.2 Turbidity Units), underlining the value addition obtained in using measurement derived values in place of SoDA values.The values obtained from the study may be used to yield better estimates of clear-sky solar radiation for Zimbabwe. A better estimate of the clear-sky solar radiation will in turn improve the accuracy of the global radiation estimates from satellite based methods.

Indirect determination of broadband turbidity coefficients over Egypt

Long-term data from diffuse and global irradiances were used to calculate direct beam irradiance which was used to determine three atmospheric turbidity coefficients (Linke TL, Angstrom β and Unsworth–Monteith δa) at seven sites in Egypt in the period from 1981 to 2000. Seven study sites (Barrani, Matruh, Arish, Cairo, Asyut, Aswan and Kharga) have been divided into three categories: Mediterranean climate (MC), desert Nile climate (DNC) and urban climate (UC, Cairo). The indirect method (i.e., global irradiance minus diffuse irradiance) used here allows to estimate the turbidity coefficients with an RMSE% ≤20 % (for β, δa and TL) and ~30 % (for β) if compared with those estimated by direct beam irradiance and sunphotometeric data, respectively. Monthly averages of TL, β and δa show seasonal variations with mainly maxima in spring at all stations, due to Khamsin depressions coming from Sahara. Secondary maxima is observed in summer and autumn at DNC and MC (Barrani and Arish) stations in summer due to dust haze which prevails during that season and at UC (Cairo) in autumn, due to the northern extension of the Sudan monsoon trough, which is accompanied by small-scale depressions with dust particles. The mean annual values of β, δa, and TL (0.216, 0.314, and 4.6, respectively) are larger in Cairo than at MC stations (0.146, 0.216, and 3.8, respectively) and DNC stations (0.153, 0.227, and 3.8, respectively). Both El-Chichon and Mt. Pinatubo eruptions were examined for all records data at MC, UC and DNC stations. The overburden caused by Mt. Pinatubo’s eruption was larger than El-Chichon’s eruption and overburden for β, and TL at DNC stations (0.06, and 0.58 units, respectively) was more pronounced than that at MC (0.02, and 0.26, respectively) and UC (0.05 and 0.52 units, respectively) stations. The annual variations in wind speed and turbidity parameters show high values for both low and high wind speed at all stations. The wind directions have a clear effect on atmospheric turbidity, and consequently, largest turbidities occur when the wind carries aerosols from the main particle sources, such as industrial particle sources around Cairo or to some extent from the Sahara surrounding all study stations.