The term 'Atmospheric Region with A' is composed of two crossword solutions: OZONE (5 letters) and AREA (4 letters). OZONE is a naturally occurring molecule in the Earth's atmosphere that absorbs ultraviolet radiation from the sun. It is found in the stratosphere, which is the second layer of the atmosphere. AREA is a measure of the size of a region or surface. In this context, it refers to the size of the OZONE layer in the atmosphere.