High levels of ozone and related gases over the Bay of Bengal during winter and early spring of 2001

Measurements of surface ozone and related trace gases were made over a broader region of the Bay of Bengal along with measurements over the Indian Ocean and the Arabian Sea during a Bay of Bengal Experiment (BOBEX) conducted from 18 February to 23 March, 2001. Higher levels of ozone (60–64 ppbv) were observed over the central Bay of Bengal (10–15N, 84–86E) and not near the coastal regions due to different types of wind patterns. Ozone levels in the south of 12N are observed to be higher over the Bay of Bengal than the average levels measured over the Arabian Sea during all the four INDOEX cruises conducted in each winter from 1996 to 1999. The elevated O3 level is consistent with simultaneously measured higher levels of CO, CH4 and SF6 over the Bay of Bengal. These observations together with general wind patterns, 7 days back trajectories and results from a three-dimensional model simulations suggest that higher levels of these trace gases over the Bay of Bengal are due to transport from the continent. These results also suggest that the air over the Bay of Bengal was found to be more polluted than the Arabian Sea during this season.