Which action can lead to an increase in air pressure?

An increase in air pressure is associated with an increase in the density of air. When air density increases, more air molecules occupy a given volume, leading to a higher mass of air above a certain point. This results in greater pressure being exerted on the surface.

Factors that influence air density include temperature, altitude, and humidity. As air temperature increases, air typically expands and becomes less dense, which can decrease air pressure. When altitude increases, the air becomes less dense due to the decrease in the number of air molecules above a certain point, which also leads to lower pressure.

On the other hand, humidity plays a significant role in air density. When humidity increases, the density of air typically decreases because water vapor (molecular weight of about 18) is lighter than dry air (which has a higher average molecular weight). Therefore, decreasing humidity can also contribute to an increase in air density and, consequently, air pressure.

In summary, increasing the density of air directly leads to an increase in air pressure, making it the correct answer.