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Abstracto

Diurnal and seasonal characteristics of ozone and NOx over a high altitude Western Ghats location in Southern India

C. Udayasoorian, R. M. Jayabalakrishnan, A. R. Suguna, S. Venkataramani and Shyam Lal

Continuous measurements of ozone and NOx concentrations were made over a period of two years from a high altitude location Ooty in the Nilgiris Mountain Range in southern India to characterize the diurnal and seasonal variations. The ozone and NOx concentrations were higher during warmer months and prominent seasonal variations were recorded. A seasonal variation in ozone showed a pronounced maximum (62 ppb in March) in summer with values sometime exceeding 90 ppb and a minimum in the monsoon and post monsoon season (17 ppb in August). Interestingly, diurnal pattern of ozone did not show any day time build up throughout the study period. On the contrary, lower ozone mixing ratio was observed during the day. A monthly maximum NOx value was observed during summer month of April (1.85 ppb), whereas minimum value was observed during monsoon (0.19 ppb in August). Further, low rainfall, high temperature and solar radiation have given rise to the gradual build up of ozone during summer and winter. The unique meteorology over this region seems to play an important role in seasonal and as well as diurnal variation of ozone. Regional pollution is shown to have maximum contribution to ozone level during February to May