<p>To investigate the monthly mean variability on average BC mass concentration, the individual day values are grouped into 24-hour periods, sunlight hours, night hours and complete average day-to-day changes in the 24-hour average BC values. Sunlight hours BC values and Night Hours BC level variation along with mean monthly BC aerosols levels for the complete study period from March, 2009 to Feb., 2014. Average monthly BC aerosols magnitudes are illustrated that during entire study period of BC observation, a large day to day BC aerosols variations in their 24 hourly average, Sun light hours along with, night time hours values occur within ranges of 0.12 to 12.16 &micro;g m-3, 0.95 to 14.29 &micro;g m-3 and 0.12 to 16.87 &micro;g m-3, respectively Their annual mean values of above study period as well as Annual BC behaviors clearly reveal peak during December and January (~6.5 to 10 &micro;g m-3), a gradual decline to the annual lowest (~0.7 to 1.8 &micro;g m-3) attained during May through September months (summer and monsoon) with a maximum to minimum monthly BC values ratio of &gt;6. The overall combined annual long-term means BC level value of five years at Jaisalmer is 2.3&plusmn;1.9 &micro;g m-3 for the whole day mean BC levels.</p>

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