Variations of trace gases over the Bay of Bengal during the summer monsoon

  • I A GirachEmail author
  • Narendra Ojha
  • Prabha R Nair
  • Yogesh K Tiwari
  • K Ravi Kumar


In situ measurements of near-surface ozone (\(\hbox {O}_{3})\), carbon monoxide (CO), and methane (\(\hbox {CH}_{4})\) 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. \(\hbox {O}_{3}\), CO and \(\hbox {CH}_{4}\) 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 \(\hbox {O}_{3}\) from satellite retrievals is found to be similar to that in surface \(\hbox {O}_{3}\) 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 of 1.6 ppbv, –2.6 ppbv and 0.07 ppmv for \(\hbox {O}_{3}\), CO and \(\hbox {CH}_{4}\), respectively. The analysis of diurnal variation of \(\hbox {O}_{3}\) 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 \(\hbox {CH}_{4}\) variations as measured by in situ sample analysis highlighting the need of more shipborne in situ measurements of trace gases over this region during monsoon.


Ozone carbon monoxide methane monsoon Bay of Bengal MACC reanalysis 



We thank CTCZ and ICRP organizers for providing the opportunity to participate in the CTCZ experiment. We are thankful to the Director, National Centre for Antarctic and Ocean Research (NCAOR), Goa for providing shipboard facilities. The AIRS \(\hbox {CH}_{4}\) mixing ratios were obtained from website The MACC reanalysis data were obtained from and we greatly acknowledge MACC Reanalysis project. The Dutch-Finnish-built OMI is part of the NASA EOS Aura satellite payload. The OMI project is managed by NIVR and KNMI in the Netherlands. The tropospheric ozone data were obtained from The comments and suggestions from two anonymous reviewers are gratefully acknowledged.


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Copyright information

© Indian Academy of Sciences 2018

Authors and Affiliations

  • I A Girach
    • 1
    Email author
  • Narendra Ojha
    • 2
  • Prabha R Nair
    • 1
  • Yogesh K Tiwari
    • 3
  • K Ravi Kumar
    • 4
    • 5
  1. 1.Space Physics LaboratoryVikram Sarabhai Space CentreThiruvananthapuramIndia
  2. 2.Department of Atmospheric ChemistryMax Planck Institute for ChemistryMainzGermany
  3. 3.Indian Institute of Tropical MeteorologyPuneIndia
  4. 4.National Institute of Polar ResearchTachikawaJapan
  5. 5.Department of Environmental Geochemical Cycle ResearchJAMSTECYokohamaJapan

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