Q : Before regular meditation we do purification of the atmosphere around us. Is this required when we do meditation during work, walk etc.?

A : Not necessary. But it is better to keep the atmosphere Divine. For this purpose, it is not difficult to start your meditation saying "the atmosphere around me is purified by the Divine Power", whenever and wherever you meditate. Even a fraction of a second will do. That thought itself will bring harmony and peaceful energy around you. Even otherwise there will be no negative effect. Only there may be some loss of benefit to you.