Temporal variations in surface ozone at Thumba (8.6°N, 77°E) -: a tropical coastal site in India

Surface measurements of ozone and meteorological parameters are made at a tropical coastal site, Thumba (8.6degreesN, 77degreesE, 2m) in India from April 1997 to March 1998. Ozone shows a diurnal variation with daytime higher levels and a sharp change in its values during evening time. The evening time change in ozone values with a secondary peak is found to be due to change in wind pattern from sea-breeze to land-breeze at this site. This secondary peak in ozone is weakest during monsoon period. A detailed study of the meteorological parameters shows that during nighttime, polluted air from land side moves to the nearby marine region relatively increasing the levels of ozone and precursor gases. Observations show that the onset time of daytime ozone increase and its rates are related with each other. If onset time of ozone increase is early, its increase rate is slower and vice versa. Maximum ozone levels are observed to be during March, probably due to intense photochemical production. However, this is different when compared to other Indian site like Ahmedabad, where maximum ozone levels are observed during late autumn and early winter. Monthly average ozone levels are observed to be very low (in the range of 13-22 ppbv) at Thumba. (C) 2002 Elsevier Science Ltd. All rights reserved.