What condition is most likely to exist when an air mass is stable?

When an air mass is stable, it typically means that there are limited vertical movements within the atmosphere. In stable conditions, the air near the surface tends to remain layered and can trap pollutants like smoke, dust, and haze at lower levels. This layer prevents these particles from dispersing into higher altitudes, often resulting in decreased air quality and poor visibility.

The concentration of smoke, dust, and haze at lower levels due to stability can lead to fog, smog, and other visibility-reducing phenomena. The inability for the air to mix vertically means that pollutants accumulate rather than disperse, creating unhealthy conditions for air quality.

In contrast, other options describe scenarios that are associated with instability or dynamic weather conditions. For example, severe thunderstorms are typically formed in unstable air masses where there is significant vertical lift, and high winds and clear skies generally occur in a more stable atmosphere, but without the concentration of pollutants mentioned in the correct choice.