Abstract: Attenuation of solar irradiance is strongly dependent on conditions of the sky, cleanliness of the atmosphere, and composition of gaseous constituents. In a clean and dry atmospheric condition, solar irradiance is attenuated by permanent atmospheric constituents of air molecules, gases and ozone, whose contents are nearly invariable. Two additional attenuation processes, which are the absorption by water vapour and scattering by aerosol particles, take place in a real atmosphere. The additional attenuation caused by these two processes is known as being due to the turbidity of the atmosphere.
The complexity of phenomena involved in the attenuation processes causes difficulty in computation of solar irradiance reaching the earth’s surface, especially in certain climatic conditions.
The study of atmospheric turbidity is important in meteorology, climatology and for atmospheric pollution monitoring. Information on solar irradiance on the earth’s surface is necessary for application of solar energy, for the determination of the amount of spectral global irradiance for the photovoltaic cells designing and for the selective absorbers for spectral thermal collectors.
The proposed study of the turbidity factor is carried out in order to develop a possible method for estimating solar radiation. In this paper, the turbidity factor is calculated for solar radiation data from Brasov with the intention of finding a variation model of this; all the conclusions are very useful in the development of a mathematical model of the solar radiation for the urban area of Brasov.
Atmospheric turbidity is an important parameter for assessing the air pollution in local areas, as well as being the main parameter controlling the attenuation of solar radiation reaching the Earth’s surface under cloudless sky conditions. The paper proposes a study of the Linke’s and Angstrom turbidity factors, calculated on the basis of the meteorological data recorded during three years, in Brasov urban area. The obtained results will be presented as comparative diagrams (variation of the monthly mean values depending on time).
The turbidity determination will be made using a few broadband models and the present study will present for every model proposed the necessary stages.
It must be mentioned that the technical literature does not offer very accurate values of the turbidity factors; besides, it does not take into consideration the geographical, climatic and urban conditions specific to Brasov area (for instance, according to specialised literature, the monthly mean values of the turbidity factor varies between 1.9 and 3.5).

Brief Biography of the Speaker:
Elena EFTIMIE is professor at the Department of Product Design and Robotics, from Transilvania University of Brasov (Romania). From November 2000 she is Doctor Engineer (MAGNA CUM LAUDE) in the field of Mechanical Engineering; the title of the Ph.D. thesis: Researches concerning the functional performances of the safety intermittent automatic clutches. As academic positions, from October 2006 – present, she is Professor at “Transilvania” University of Brasov, Department of Product Design and Robotics; from October 2003 – September 2006: Senior Lecturer; from February 1999 – September 2003: Lecturer; from September 1995 – February 1999: Professor assistant; September 1992 - September 1995: Laboratory Instructor. Regarding her scientific activities, she authored or co-authored 107 scientific papers published in reviewed journals or presented at international conferences (58 scientific papers as first and single author, 41 scientific papers at international conferences, 31 scientific papers published abroad, 12 monographs, 5 as single author and 1 as first author, 25 research projects of which 2 as project manager). Concerning other activities there are mentioned: she was Teaching Professor, 6-17 July, at RESchool 2009, Technological Educational Institute of Crete, Chania, Greece and she is Vice-President of Brasov subsidiary: Romanian Association of Mechanical Transmission.