In situ measurements of near-surface ozone (O₃), carbon monoxide (CO), and methane (CH₄) were carried out over the Bay of Bengal (BoB) as a part of the Continental Tropical Convergence Zone (CTCZ) campaign during the summer monsoon season of 2009. O₃, CO and CH₄ mixing ratios varied in the ranges of 8–54 ppbv, 50–200 ppbv and 1.57–2.15 ppmv, respectively during 16 July–17 August 2009. The spatial distribution of mean tropospheric O₃ from satellite retrievals is found to be similar to that in surfaceO₃ observations, with higher levels over coastal and northern BoB as compared to central BoB. The comparison of in situ measurements with the Monitoring Atmospheric Composition & Climate (MACC) global reanalysis shows that MACC simulations reproduce the observations with small mean biases of1.6 ppbv, –2.6 ppbv and 0.07 ppmv for O₃, CO and CH4, respectively. The analysis of diurnal variation of O₃ based on observations and the simulations from Weather Research and Forecasting coupled with Chemistry (WRF-Chem) at a stationary point over the BoB did not show a net photochemical build up during daytime. Satellite retrievals show limitations in capturing CH₄ variations as measured by in situ sample analysis highlighting the need of more shipborne in situ measurements of trace gases over thisregion during monsoon.

Climate impacts agriculture in various complex ways at different levels and scales depending on the local natural crop growth limitations. Our objective in this study, therefore, is to understand how different is the atmosphere–biosphere exchange of $\rm{CO_{2}}$ under contrasting subtropical and boreal agricultural (an oilseed crop and a bioenergy crop, respectively) climates. The oilseed crop in subtropical climate continued to uptake $\rm{CO_{2}}$ from the atmosphere throughout the year, with maximum uptake occurring in the monsoon season, and drastically reduced uptake during drought. The boreal ecosystem, on the other hand, was a sustained, small source of $\rm{CO_{2}}$ to the atmosphere during the snow-covered winter season. Higher rates of $\rm{CO_{2}}$ uptake were observed owing to greater day-length in the growing season in the boreal ecosystem.The optimal temperature for photosynthesis by the subtropical ecosystem was close to the regional normal mean temperature. An enhanced photosynthetic response to the incident radiation was found for the boreal ecosystem implying the bioenergy crop to be more efficient than the oilseed crop in utilizing the available light. This comparison of the $\rm{CO_{2}}$ exchange patterns will help strategising the carbon management under different climatic conditions.