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UV INDEX ESTIMATION FROM UV RADIOMETERS AND BREWER MEASUREMENTS

by
Mahalakshmi P,
M.Sc. Physics,
Madurai Kamaraj University,
Madurai.

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Guided by
Dr M. Venkat Ratnam,
Scientist,
National Atmospheric Research Laboratory(NARL),
Department of Space(DoS), Govt of India,
Gandanki.

Project period: 7 May 2018- 6 July 2018
Date :
Contents

ABSTRACT……………………………………………………………………………. 1

INTRODUCTION……………………………………………………………………. 1

INSTRUMENTATION……………………………………………………………… 2

METHODOLOGY…………………………………………………………………… 3

RESULTS AND CONCLUSION………………………………………………… 4

REFERENCES………………………………………………………………………… 5

ACKNOWLEDGEMENTS………………………………………………………… 6

ABSTRACT
This project is mainly based on the ultraviolet radiation. Nowadays the weather conditions are becoming worse during summers which are unbearable. This is because of the solar ultraviolet radiation. The intense effect of it causes global warming. Studies says that there is no increase in the amount of suns radiation. The effect we observe is due to the decrease of UV absorbing factors. The ultraviolet radiation reaching earth can cause many health disorders in living beings. To safeguard the living beings from the effect of ultraviolet radiation is making the people aware of the daily intensity of UV reaching the surface of earth. For this purpose, Canada introduced a term called ULTRAVIOLET INDEX in the year 1992. This work is to estimate the UV index for Gadanki which is situated in Andhra Pradesh. The aim of this work is to make people aware of the UV intensity and make preventive measures before exposure to it.

INTRODUCTION
ULTRAVIOLET RADIATION:
Sun is radiating continuous spectrum which includes the radiations of all wavelengths. They range from gamma rays with wavelength < 10^-12 m , X-rays ( =1mm). Among these the most dangerous is UV radiation, though it has some beneficial characters. The only this which acts as a natural safeguard from UV is the OZONE LAYER. It is the layer in atmosphere absorbing the UV radiation coming from sun. The UV is divided into three parts UV-A, UV-B, UV-C.
Their wavelengths are,
UV-A – 315nm to 400nm
UV-B – 280nm to 315nm
UV-C – 100nm to 280nm
In these , UV-C is completely absorbed by the ozone layer, about 90% of UV-B is absorbed by ozone and 10% of it is transmitted to the surface of the earth, UV-A is insensitive to ozone and it is not absorbed by ozone. UV-A is completely transmitted to the surface of earth. UV-B affects only the upper epidermis of the skin while UV-A can penetrate deep into the skin. Longer exposure to such radiations cause skin cancer, melanoma and other serious health disorders. To get rid of these some preventive measures must be taken.

ULTRAVIOLET INDEX:
To inform people how the UV is intense day to day and about the preventive measures, a term UV INDEX is introduced by Canada. The UV index is a measure of the solar irradiance simply represented by a scale graduated in numbers starting from 0(zero) and there is no end. It is an open-ended scale. The different values show the level of solar irradiance, from that we can understand what the preventions are to be done.
• 0 to 2 – low
• 3 to 5 – moderate
• 6 to 7 – high
• 8 to 10 – very high
• Above 10 – extremely high
The low values need no preventions. The values above 2 is dangerous and so preventions such as using sunglasses, brimmed hat, sunscreens, sun protective clothing should be taken. It is better to avoid outdoors during the noon time 10 am to 2 pm in a high UV index day. This is estimated in different ways which are discussed in upcoming topics. Here we are using the data obtained from UV radiometers and Brewer spectrometers to estimate the UV index. There are many factors affecting UV index.

FACTORS AFFECTING UV INDEX:
The factors affecting UV index are as follows.
• Latitude
• Altitude
• ozone
• Clouds
• Elevation of sun
• Time of day
• Reflectivity ,surface pollution and aerosols.
LATITUDE :
The latitude affects the UV index in such a way that the index in high at the equator than the latitudes towards north pole and south pole.
ALTITUDE:
When there is increase in altitude , there is increase in UV index. Because the air at higher altitude is thin to absorb the ultraviolet radiation.
OZONE:
Ozone plays a major role in affecting UV index. As this is a significant layer in atmosphere to absorb the harmful radiations coming from sun. It absorbs all UV-C, most of UV-B and not the UV-A as it is insensitive to it. Greater the level of ozone in atmosphere lesser will be the UV index.

CLOUDS:
Clouds can reflect, transmit, or absorb UV radiation. As the cloud cover increases, the chance of reflection increases. The transmission depends on the type of cloud.
• Clear sky transmits 100%
• Scattered clouds 89%
• Broken clouds 73%
• Overcast sky 31%
ELEVATION OF SUN:
When the sun is exactly at right angle , then the UV index is higher. And at acute and obtuse angles, the index gradually decreases. The rays of the sun take minimum time to reach the surface if it is at the direct angle and so more intense than when the path is longer.
TIME OF DAY:
The time of day determines the solar zenith angle. This is the angle between the zenith and the centre of the sun. Therefore, the index is higher at noon time then the forenoon and afternoon.
REFLECTIVITY:
The things near us can reflect or scatter the radiation. Snow reflects 80% radiation, sand reflects 15% , water reflects 10%,concrete reflects 12% and grass reflects 5% of radiation.
SURFACE POLLUTION AND AEROSOLS:
The aerosols in the atmosphere absorbs the UV radiation and thus reducing the UV index values. The pollution plays both the roles, it can either reduce or enhance the UV index. It absorbs the radiation, reducing the index. Meanwhile it causes ozone depletion, enhancing the UV index.

REFERENCES:
• https://www.verywellhealth.com/know-your-uv-index-1069524
• https://qsun.co/is-it-true-that-air-pollution-absorbs-uv-rays/

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