"Atmospheric density" refers to how much air particles are packed together in the Earth's atmosphere. It measures how thick or thin the air is in a specific area. Full definition
The speed of release is again dictated by overall atmospheric density because greater density renders it less likely that the neighbouring molecules are cool enough for a release of radiant energy to occur. (newclimatemodel.com)
The increased warmth allows the atmosphere to hold more water vapour so that total atmospheric density increases and the atmospheric greenhouse effect strengthens. (newclimatemodel.com)
If so, How does atmospheric density affect the temperature? (realclimate.org)