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, NO_x, 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.