Atmospheric Chemistry Group
Physical Research Laboratory, Ahmedabad 380009
The tropical region is a major global chemical laboratory, where chemical processes are faster due to intense solar radiation. It is also the entry region to the global atmosphere for various trace gases emitted due to natural and man made processes from the earths surface. The focus of our group research activities is to understand the effects of physical and chemical processes on the composition of the tropical atmosphere and its perturbation by human activities. The approach includes measurements of trace gases using ground based and various platforms (balloon, ship, aircraft etc) as well as modeling of atmospheric chemistry. Our research can be classified in two broad categories:

Tropospheric processes:  Ozone in the troposphere is only about 10% but plays an important role as a green house gas. Higher levels of ozone in the troposphere can also have adverse effects on human health and plants. It is chemically produced by trace gases such as carbon monoxide, oxides of nitrogen, hydrocarbons etc. emitted from various kinds of fossil and biomass burning.

Our focus in this area is to study the sources, distribution and transport of ozone and related trace gases. This is acchived through the following programmes:

1. Study of trace gas chemistry over Marine regions:-

(a) Bay of Bengal


(c) JGOFS - India

2. Transport and transformation of trace gases over continental regions

3. New programs to study STE:-

(a) Balloonsonde

(b) Differential Absorption Lidar (DIAL)

4. ozone chemistry, transport and budget studies using a chemical transport modeel

Stratospheric processes:  About 90% of Ozone is present in the stratosphere where it absorbs the biologically harmful solar ultraviolet radiation and protects life on Earth. Large ozone depletion has been found to occur especially over the polar regions due to man made chlorofluorocarbons (CFCs). Thus most processes in this region are linked to ozone chemistry. Through observations and modelling of ozone and related trace gases, we study the impact of these on the chemical, radiative and physical processes in the stratosphere.

Vertical profiles of ozone and trace gases using Rocket and Balloon

To study the distribution of trace gases (especially CFCs) in the stratosphere, we have conducted high altitude balloon flights from Hyderabad, India. The initial three flights were in collaboration with Max Planck Institute, Germany, the first one launched in 1985. Later, a indigenous cryogenic air sampler was developed jointly with ISRO and flown successfully in 1994 and 1998. Profiles of a large number of trace gases including CFCs, SF6, CH3Br etc. have been observed from Hy- derabad. Total Cl loading has also been calculated from these measurements.

Modelling trace gases in stratosphere

The observed trace gases have been compared with simulations from a 2-D chemical trasport model from MPIC, Mainz (Germany) and now with us at PRL. SF6 is a useful tracer and was included in the 2-D model to validate the vertical transport mechanism of the model. Sharp gradient above 15 km and extremely weak gradient above 25 km in the observations from Hyderabad are due to dynamical effects.
This page was updated on 5 Oct 2006
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