Why there is a huge difference in temp in day and night in rajasthan inspite greenhouse gases?

The sky above a desert region like Rajasthan is usually very clear. There is very little moisture in the air in the deserts. Water acts to trap infrared radiation from both the sun and the ground, and dry desert air is incapable of blocking sunlight during the day or trapping heat during the night. Thus, during daylight most of the sun's heat reaches the ground. The ground absorbs most of the sunlight that strikes it -- heating the surrounding air. At night the reverse happens. The hot ground (and air) radiate the heat absorbed during the day back into space causing the temperature to drop rather rapidly. Hence the desert cools quickly.