[1] The measurements of vertical distribution of ozone have been made over the Bay of Bengal and the Arabian Sea in spring 2006 during a cruise campaign, namely, the Integrated Campaign for Aerosol, Gases and Radiation Budget. The average tropospheric columnar ozone (TCO) values are found to be 36.1 AE 6.9 Dobson unit (DU) and 41.7 AE 5.0 DU over the Bay of Bengal and the Arabian Sea, respectively. In contrast to TCO, ozone mixing ratios are higher by about 10 ppbv in the lower 3 km over the Bay of Bengal due to Indo Gangetic outflow above the marine atmospheric boundary layer. Major contribution in the higher TCO value over the Arabian Sea is, possibly, by stratospheric intrusion when ozone in the upper troposphere is higher by about 20 ppbv. The lowest columnar ozone content of 22.4 DU was observed on 30 March in the central Bay of Bengal due to convective activity resulting into lower ozone throughout the troposphere, except between 6 and 10 km altitude. These near simultaneous ozone observations over the Bay of Bengal and the Arabian Sea in spring season have revealed the role of regional and long-range transport and local dynamics on the vertical distribution of ozone over these tropical marine regions.

[1] Measurements of vertical distributions of ozone and meteorological parameters were made over the Bay of Bengal (BOB) and Arabian Sea (AS) from ocean research vessel Sagar Kanya during the period of 18 March to 10 May 2006 as a part of the Integrated Campaign for Aerosols, Gases and Radiation Budget (ICARB). The observations showed a highly polluted layer (average ozone ∼68.0 ± 10.1 ppbv) over the northern BOB as compared to the northern AS (51.5 ± 7.6 ppbv), southern BOB (42.7 ± 12.8 ppbv), and southern AS (40.9 ± 9.5 ppbv) in the altitude range of 1-3 km. In this altitude range, specific humidity was lower by about 2-6 g/kg, and temperature was higher by 1°C-3°C over the northern BOB and northern AS as compared to their southern counterparts. This comparison and the total potential source contribution function analysis indicate that the observations over the northern BOB and the northern AS were influenced by the transport of continental air masses. The outflow from the polluted atmosphere over northern India, particularly over the Indo-Gangetic Plain, resulted in higher mixing ratios of ozone over the northern BOB. The air masses from the northern Indian region contributed an enhancement of about 13 ± 6 ppbv to the mixing ratio of ozone over the BOB in the altitude range of 0.75-3.0 km. The mixing ratios of ozone in the unperturbed marine air masses were found to be 11 ± 6 and 5 ± 2 ppbv lower than the average ozone over the BOB and AS, respectively. These results clearly show the outflow of continental air containing high ozone and possibly other pollutants over the northern BOB, which can have significant implications in the chemistry and climate of relatively cleaner regions.

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