Variation of ozone column density over sri lanka using solar UV radiation received at ground level

Abstract

Ozoneisa gaswithits moleculecontainingthreeoxygenatoms,blue in colourandhas a strongpungentodor. The depletion of ozone layer is a global issue and not just a problem limitedto the countries in the polar region. Concern about the ozone depletion has an obviousbasis; the ozone layer reduces the amount of harmful UV-B radiation in the wavelengthrange of 280-315 nm from the sun that reaches the earth surface. Total amountof ozone molecules occupying a column overhead, widely known as the ozone columndensity, is measured in many countries all over the world to understand the amountof harmfulUV-B radiation reaching to the earth surface and to study the recovery rateof depletedozone layer. Thisstudy describes an attempt made to study the ozone columnar density in various locationsin Sri Lanka. To the best of our knowledge this is the first time that such a groundbased study has been carried out in Sri Lanka. Measurements were conducted in sixplacesColombo, Galle, Hambanthota , Monaragala , Diyatalawa and Kandy during theperiodNovember 2002 to May 2003. A MICROTOPII 5-channel Ozone Monitor & Sun Photometer tested and calibrated usingDobson Spectrometer was used for the measurement. The instrument measures directsolar radiation at 300.0, 305.5, and 312.5 nm windows and calculate the ozone columndensity in Dobson Units. Hourly ozone column density data between 0800 h to 1700h were obtained and downloadedto a computer connectedto the instrument. Accuratelocation parameters needed for ozone calculation were obtained using a GPS instrument.Data were analyzed using Minitab Statistical package. Thehighestozone density was observed at the noon and the results tally with those of internationalmeasurements. The average ozone columnar density value over Sri Lanka obtainedfor these seven month period was (2831:20) DU with maximum value 385 DU recordedin June and minimum 215 DU in February. The monthly variation of ozone columnardensitymeasured over Sri Lanka is found to be tally with that of satellite data