The atmosphere is absorbing 3 units of energy (labelled 1, 2, and 3 in the figure above).  The atmosphere must also emit 3 units of energy (the purple arrows).

The ground is absorbing 1 unit of sunlight (green arrow striking the ground at the left side of the figure).  The ground is emitting 3 units (the three upward pointing orange or red arrows).  The atmosphere needs to send 2 of its 3 units of emitted energy downward toward the ground to put the ground into energy balance.

The atmosphere sends 1 unit of energy upward into space.  There are two arrows of sunlight arriving at the top of the earth's atmosphere and 2 arrows of energy leaving the atmosphere and going back into space.