Surface temperature differences in turn cause pressure differences. A hot surface warms the air above it causing it to expand and lower the density and the resulting surface air pressure. The resulting horizontal pressure gradient moves the air from higher to lower pressure regions, creating a wind, and the Earth's rotation then causes deflection of this air flow due to the Coriolis effect. The simple systems thus formed can then display emergent behaviour to produce more complex systems and thus other weather phenomena.  Large scale examples include the Hadley cell while a smaller scale example would be coastal breezes.
Context: In Steve's kitchen, there are two burners. Burner A is currently not turned on, and burner B is set to "medium." Steve was planning on cooking some fried eggs for lunch, but is currently distracted by an article in the newspaper that was deliver to his door.
Question: The air above which burner is expanding?