When does atmospheric stability typically decrease?

Atmospheric stability typically decreases during sunny days because the heating of the Earth's surface leads to the warming of the air near the ground. As the surface absorbs solar energy, it warms up, causing the air above it to rise. This upward movement of warmer air creates convective currents, which promote mixing in the atmosphere. When the air near the surface becomes warmer than the air aloft, conditions become unstable, allowing for a greater potential for vertical mixing and dispersion of pollutants.

In contrast, during cool nights, stable conditions are usually present. The ground cools rapidly, and the air close to the surface can become cooler than the air above, leading to a temperature inversion where the cooler air is trapped beneath warmer air, suppressing vertical mixing. High humidity can also maintain stability because moist air is less dense than dry air, but it does not inherently destabilize the atmosphere. Low wind speeds contribute to stability by limiting the mixing and turbulence in the lower atmosphere. Therefore, sunny days are associated with conditions that favor instability and increased atmospheric dispersion.