Which of the following best describes the characteristic of a stable air mass?

A stable air mass is characterized by its ability to resist vertical movement, which is exactly why it inhibits vertical mixing. In a stable atmosphere, any rising parcel of air will tend to sink back to its original level instead of continuing to rise. This is often due to temperature inversions, where warmer air traps cooler air at the surface, creating a layer that resists upward motion. As a result, pollutants and moisture can become trapped near the ground, leading to a buildup in concentration as they are not dispersed into the atmosphere effectively.

In contrast, an unstable air mass allows for vertical mixing, where air parcels can rise and fall freely, facilitating the dispersal of pollutants. While high humidity can be a feature of a stable air mass, it is not definitive since humidity levels can vary independently from air stability. Finally, the flow of air with the terrain might describe certain weather conditions but does not specifically address the characteristics of stability in an air mass.