It's a combination of 1) the architectural design of the roof which allows sun to come through + 2) the Chinese refuse to crank up the air conditioning this early in the year. They use guideline of outside temperature rather than have smart controllers that detect inside temperature. Plus 3) positioning of the lounges on that mezzanine. Heat rises. The lower (shopping concourse/gate) level is usually more comfortable temperature-wise. The phenomenon you are experiencing tends to be worse in climatic swing season of late April through early June.