2. Materials and methods

Sampling Procedure and Sampling Stations
Sampling Stations:
The sampling strategy for this study involved simultaneous collection of a pair of samples of ambient atmospheric water vapor by two different methods, namely, (1) complete cryogenic trapping at -78°C; and (2) liquid condensation at 0°. The sampling was done at three stations (Ahmedabad, Latitude:23.0225°N, longitude:72.5714°E; Hyderabad, Latitude:17.3850°N, longitude:78.4867°E; and Roorkee, Latitude:29.8543°N, longitude:77.8880°E;) located far away from each other in different parts of India and having different hydrometeorological aspects. The sampling at Ahmedabad, Hyderabad and Roorkee was carried out respectively by Physical Research Laboratory (PRL), National Geophysical Research Institute (NGRI) and National Institute of Hydrology (NIH) under the aegis of IWIN National Programme, using the same procedure and devices as described below.
Ahmedabad is a city in warm semi-arid western India with annual average rainfall of 80 cm received on ~35 rainy days during rainy season of southwest (SW) summer monsoon in the months of June to September. Hyderabad is a city in south-eastern India and has predominantly a tropical wet and dry climate with average annual rainfall of 76.6 cm. It receives its 76% of annual rain during southwest summer monsoon and remaining 24% during northeast (NE) winter monsoon. Roorkee is in north India and has a warm and temperate climate. It receives annual rainfall of 117 cm of which 59-84% received in SW monsoon season and remaining in NE winter monsoon season.