Atmospheric Trace gases-Chemistry, Transport and Modelling Project under ISRO-GBP

Atmospheric Trace gases-Chemistry, Transport and Modelling (AT-CTM) project is one of the major national projects under Geosphere Biosphere Programme of ISRO (ISRO-GBP) initiated in 2007. The nodal agency is Physical Research Laboratory, Ahmedabad. SPL is a major component of this project. 

The chemical composition of the atmosphere is a key factor in all biological activities on earth and global climate. The atmosphere of Earth comprises of ~78% of nitrogen and ~21% oxygen by volume. The remaining 1% include gases like Argon (Ar), carbon dioxide (CO2), ozone (O3), carbon monoxide (CO), ammonia (NH3), oxides of nitrogen, sulphur bearing gases, hydrocarbons, halogen containing species, water vapour etc. Apart from these minor/trace species, the solid/liquid particulate matter called aerosols also exist in the atmosphere. The gaseous components present in parts per million (ppm)/parts per billion (ppb)/parts per trillion (ppt) by volume of the atmosphere are generally referred to as the trace gases. In spite of their low concentration levels, these trace gases play vital roles in the Geosphere- Biosphere system acting as Green house gases, air pollutants affecting plants/animals/humans/material and controlling atmospheric chemistry. 

As part of this project an exclusive Environmental Observatory has been set up at SPL for the measurement of atmospheric trace gases O3, NOx, CO, SO2, CH4 and CO2. Sophisticated on line gas analyzers are operational for continuous measurement of these gases. Participating in campaigns like ICARB (Integrated Campaign for Aerosol, gases and radiation budget) under ISRO-GBP, CTCZ (Continental Tropical Convergence Zone) experiment under Indian Climate Research Program (ICRP), and International Indian Ocean Expedition (IIOE-2) extensive ship-based measurements of O3, NO2, CO, were carried out over Bay of Bengal (BoB) as well as Arabian Sea and the spatial distribution of these gases were brought out. Ozone sondes flown on Balloons provide the vertical profile of Ozone. In addition, satellite-based data on trace gases has been utilized to understand their global patterns, long-term trends and long-range transport. On-line gas analysers are operated at the high altitude site Ponmudi with a view to have information on back ground conditions. The gas analysers were also operated at Antarctica as part of polar studies. Photochemical Box Model and WRF-Chem model are being used to understand the spatio-temporal behaviour of the trace gases.


SPL Team

  1. Dr. Girach Imran Asatar (Principal Investigator)
  2. Mrs. Revathy S. Ajayakumar




  1. Girach I. A., Nair P. R., Ojha N., and Sahu L. K., "Tropospheric carbon monoxide over the northern Indian Ocean during winter: influence of inter-continental transport", Climate Dynamics, 2020. (
  2. Girach I. A., Tripathi N., Nair P. R., Sahu L. K., and Ojha N., "O3 and CO in the South Asian outflow over the Bay of Bengal: Impact of monsoonal dynamics and chemistry", Atmospheric Environment, 233, 117610, 2020. (
  3. Kavitha M., Nair P. R., Girach I. A., Aneesh S., Sijikumar S. and Renju R., "Diurnal and seasonal variations in surface methane at a tropical coastal station: Role of mesoscale meteorology", Science of the Total Environment, 631–632, 1472–1485, 2018. (
  4. Girach I. A., N. Ojha, Prabha R. Nair, Y. K. Tiwari and K. Ravi Kumar, "Variations of trace gases over the Bay of Bengal during the summer monsoon", Journal of Earth System Science, 127, 15, 2018. (
  5. Girach I. A., N. Ojha, P. R. Nair, A. Pozzer, Y. K. Tiwari, R. K. Kumar and J. Lelieveld, "Variations in O3, CO, and CH4 over the Bay of Bengal during the summer monsoon season: shipborne measurements and model simulations", Atmospheric Chemistry and Physics, 17, 257-275, 2017. (
  6. Girach, I. A. and P. R. Nair, "On the vertical distribution of Carbon monoxide over Bay of Bengal during winter: Role of water vapour and vertical updrafts", Journal of Atmospheric and Solar-Terrestrial Physics, 117, 31–47, 2014. (
  7. Nair, P. R., L. M. David, S. Aryasree and K. S. George, "Distribution of ozone in the marine boundary layer of Arabian Sea prior to monsoon: Prevailing airmass and effect of aerosols", Atmospheric Environment, 74, 18-28, 2013. (
  8. Girach, I. A., P. R. Nair, L. M. David, P. Hegde, M. K. Mishra, G. M. Kumar, S. Murali Das, N. Ojha and M. Naja, "The changes in near-surface ozone and precursors at two near-by tropical sites during annular solar eclipse of 15 January 2010", Journal Geophysical Research, 117(D01303), 2012. (
  9. David, L. M., I. A. Girach and P. R. Nair, "Distribution of ozone and its precursors over Bay of Bengal during winter 2009: Role of meteorology", Annales Geophysicae, 29, 1613-1627, 2011. (
  10. David, L. M. and P. R. Nair, "Diurnal and seasonal variability of surface ozone and NOx at a tropical coastal site: Association with mesoscale and synoptic meteorological conditions", Journal Geophysical Research, 116(D10303), 2011. (
  11. Nair, P. R., L. M. David, I. A. Girach and K. S. George, "Ozone in the marine boundary layer of Bay of Bengal during post-winter period: Spatial pattern and role of meteorology", Atmospheric Environment, 45, 4671-4681, 2011. (
  12. Girach, I. A. and P. R. Nair, "Spatial distribution of near-surface CO over bay of Bengal during winter: role of transport", Journal of Atmospheric and Solar-Terrestrial Physics, 72, 1241-1250, 2010. (

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Site Last Updated: 17 January 2022