Reaction of radiometric parameters to atmospheric pollution: Part I - Variation over time

The drive for indust rial development h... ... 100 to large scale urbanisation and result,.-. d in theinjec tion of good amount of suspended particle.. and gaseous substances into the atmosphere. The m..er-abuscof the capac ity .of the atmosphere to sustain the equilibrium is bound to disturb the heal budget of the earthatmospheresystem. Radiometric parameters of the atmosphere give an early indication of the trends in the longtermclimatic changes. Whi le the global rad iant exposure is no t likely to show perceptible changes due to theincreased scauering by the pollutants, I ~ ~ diffuse radiant el(p(ls~re and the direct so.l3! irradianc~ respond qu icklyto the changes In the atmospheric conditions. Various controlling factors like humidity. soi l moist ure and cloud"have d ifferent effects on the terres trial radiant energy and the changes in thi s energy OI..'Cur slowly and ta ke longtime to affect the climate at a place. But the general trend is indicated by the increased diffuse component in thedi rect sola r rrmdiances and in the net outgoing terrestrial radia nt energy. The responses arc clearly indicative.part icularly ,II Punc......here the industrial activiti es grew at a phenomenal rate during the past fifteen years.

The diffuse component of the global solar radiation at Qena / Egypt

Diffuse solar radiation on horizontal surfaces is estimated at Qena / Egypt. The basic procedure is to develop relationships of the widespread use Liu & Jordan types between the daily global horizontal radiation (G) and its diffuse component (D) using measured values of these two quantities. An error analysis has been done for the results of diffuse radiation calculated using the regression models obtained in this paper and those estimated from other known ones of the Liu & Jordan type, According to statistical evaluation of the various relationships, it is seen that our models provide the best estimation of the diffuse radiation, Effect of climatic conditions was considered in the discussion.

The relationship of the parameters of the optical density of the sample and the absorbance of the sample material

The relationship of the parameters of the optical density of the sample and the absorbance of the sample material is studied, which is relevant for the analysis and differentiation of measurement results by devices with light flux filtration and spectral devices (densitometers and spectrophotometers). To identify the analytical dependence of the obtained values of the optical density of the sample and the absorbance of the sample material, a formula is derived for calculating the diffuse optical transmittance density if the detected radiation contains directional and diffuse components. The first term in the obtained formula characterizes the absorbance of the sample material, the second is a correction due to the diffuse component of the radiation, and is a function of the ratio of the diffuse and regular transmittances. Expressions are obtained that allow functional and quantitative determination of the relationship of the absorbance of the sample material and the parameters of the optical transmittance density of the sample. The results of calculating the absorbance of the sample material, the component of diffuse radiation, diffuse optical transmittance density and corrections of these values are presented.

Studying the ISM at ∼10 pc scale in NGC 7793 with MUSE

Context. Studies of nearby galaxies reveal that around 50% of the total Hα luminosity in late-type spirals originates from diffuse ionised gas (DIG), which is a warm, diffuse component of the interstellar medium that can be associated with various mechanisms, the most important ones being “leaking” HII regions, evolved field stars, and shocks. Aims. Using MUSE Wide Field Mode adaptive optics-assisted data, we study the condition of the ionised medium in the nearby (D = 3.4 Mpc) flocculent spiral galaxy NGC 7793 at a spatial resolution of ∼10 pc. We construct a sample of HII regions and investigate the properties and origin of the DIG component. Methods. We obtained stellar and gas kinematics by modelling the stellar continuum and fitting the Hα emission line. We identified the boundaries of resolved HII regions based on their Hα surface brightness. As a way of comparison, we also selected regions according to the Hα/[SII] line ratio; this results in more conservative boundaries. Using characteristic line ratios and the gas velocity dispersion, we excluded potential contaminants, such as supernova remnants (SNRs) and planetary nebulae (PNe). The continuum subtracted HeII map was used to spectroscopically identify Wolf Rayet stars (WR) in our field of view. Finally, we computed electron densities and temperatures using the line ratio [SII]6716/6731 and [SIII]6312/9069, respectively. We studied the properties of the ionised gas through “BPT” emission line diagrams combined with velocity dispersion of the gas. Results. We spectroscopically confirm two previously detected WR and SNR candidates and report the discovery of the other seven WR candidates, one SNR, and two PNe within our field of view. The resulting DIG fraction is between ∼27 and 42% depending on the method used to define the boundaries of the HII regions (flux brightness cut in Hα = 6.7 × 10−18 erg s−1 cm−2 or Hα/[SII] = 2.1, respectively). In agreement with previous studies, we find that the DIG exhibits enhanced [SII]/Hα and [NII]/Hα ratios and a median temperature that is ∼3000 K higher than in HII regions. We also observe an apparent inverse correlation between temperature and Hα surface brightness. In the majority of our field of view, the observed [SII]6716/6731 ratio is consistent within 1σ with ne < 30 cm−3, with an almost identical distribution for the DIG and HII regions. The velocity dispersion of the ionised gas indicates that the DIG has a higher degree of turbulence than the HII regions. Comparison with photoionisation and shock models reveals that, overall, the diffuse component can only partially be explained via shocks and that it is most likely consistent with photons leaking from density bounded HII regions or with radiation from evolved field stars. Further investigation will be conducted in a follow-up paper.

Models for the Calculation of Diffuse Radiation on Solar Collectors

For the design and exploitation of solar energy systems, information of both direct and diffuse component of solar radiation is necessary. However, the measurement data that are available are usually restricted to total horizontal irradiance. Therefore, many models have been developed to determine the diffuse component of the irradiance on solar collectors. This paper discusses the most well-known isotropic and anisotropic models for the calculation of the diffuse component of the solar irradiance. A modification of the isotropic clear day model for determining the diffuse component of solar radiation on a horizontal surface has been presented. The presented model has the same form as a simple clear day model, with the parameters determined using the least squares method and measurement data on horizontal irradiance in the region of Belgrade, Serbia. The applicability of isotropic clear day models was examined. The paper also discusses the applicability of the models for determining the diffuse irradiance on tilted collectors in real weather conditions during the year. The basic expressions are given and the characteristics of individual models are highlighted. Based on the measurement data on horizontal irradiance, the possibilities of applying different models for the calculation of the diffuse component of irradiance on solar collectors located in the region of Belgrade were examined.

The Effect of Collector Shading and Masking on Optimized PV Field Designs

Photovoltaic (PV) solar fields are deployed with multiple rows. The second and subsequent rows are subject to shading and masking by the rows in front. The direct beam incident radiation on the second row is affected by shading and the diffuse incident radiation is affected by masking, expressed by sky view factor. Hence, all rows, besides the first one, receive lower incident radiation. The design of PV fields must take into account the decrease in the incident radiation caused by these two effects. The paper investigates by simulation the annual incident diffuse, direct beam and global radiation on the first and on the second row for optimized PV fields at two sites: Tel Aviv, Israel, with low diffuse component, and Lindenberg–Germany monitoring station, with a high diffuse component. The study emphasizes the importance of the diffuse incident radiation on the energy loss of the PV field. The percentage annual global energy loss due to shading and masking on the second row amounts to 1.49% in Tel Aviv and 0.46% in Lindenberg. Isotropic and anisotropic diffuse models were considered. The calculated diffuse incident energy for the isotropic model is lower than the values for anisotropic model by about 8% in Tel Aviv and 3.75% in Lindenberg.