What primarily determines the density of air?

The density of air is primarily determined by temperature and pressure due to their direct influence on the mass and volume of air. As temperature increases, the kinetic energy of the air molecules also increases, causing them to spread apart and occupy a larger volume. This increased volume, without a corresponding increase in mass, results in a decrease in density. Conversely, when the temperature decreases, the air molecules contract, reducing the volume and increasing density.

Pressure plays a crucial role as well, particularly in how it compresses the air. An increase in pressure at a constant temperature decreases the volume of air, resulting in higher density. Conversely, if the pressure decreases, the volume increases and density decreases.

While altitude and humidity do play significant roles in the characteristics of air, they are not the primary determinants of air density. Altitude affects pressure (it decreases with higher altitude), and humidity affects the mass of the air because humid air is less dense than dry air. Wind speed is irrelevant when considering the density itself, as it pertains more to the motion of air rather than its mass and volume configuration.