Nevertheless, the N2O saturation found in the NW regions (81%; N2Oana = − 19%) was less than that of the earlier investigation (89%; N2Oana = − 11%; Naqvi et al., 1994) due to existing spatial variability and atmospheric conditions. The atmospheric pressure was decreased from 1000 hPa in the SW region to 998 hPa in the NW region associated with enhancement of wind speed from ~ 16 m s− 1 in the SW to ~ 22 m s− 1 (range of 13.1–25.5 m s− 1) in the NW region (Table 1). These atmospheric features suggest formation of cyclonic conditions in the NW region during study period. The sea-to-air flux of N2O ranged between − 27.5 and + 22.8 μmol m− 2d− 1 using LM86 whereas it
DMXAA was ranged from − 54.8 to + 45 and − 41.5 to 31.2 μmol m− 2 d− 1 using W92 and N2000 respectively (Table 1). From the average value of sea-to-air flux of N2O SW region was found to be a source to the
atmosphere (14.3 to 28.2 μmol m− 2 d− 1) due to coastal upwelling and discharge of highly saturated water from monsoonal estuaries while NW region acts as sink (− 34.6 to − 17.9 μmol m− 2 d− 1) that resulted from the discharge of undersaturated water from Ganges. Relatively higher fluxes were estimated using the W92 followed by N2000 and LM86 (Table 1). The mean sea-to-air fluxes of N2O suggest that the coastal Bay of Bengal acts as a source for atmospheric N2O (0.78 μmol m− 2 d− 1) during SW monsoon based on W92. Naqvi et al. (1994) observed that the Bay of Bengal acts as a mild source of N2O during non-monsoon period (March–April; 0.65 ± 2 μmol m− 2 d− 1) to the atmosphere using W92 parameterization. By and large Bay of Bengal acts as a mild source of N2O to the atmosphere.
