What's the difference between sunny days and sunny days?

Clear sky, Wan Li and sunny day are both words to describe sunny weather, but they are slightly different.

Clear mainly describes the weather conditions with fresh air, blue sky and no smog or other pollutants. It focuses more on describing sunny and clean weather.

Sunny days mainly refer to sunny skies and sunny weather. It emphasizes that the weather is clear, and there are no clouds or haze.

To sum up, sunny days emphasize better air quality and sunny days emphasize better weather conditions. There is no obvious semantic difference between these two words, so we can choose to use them according to the specific context and usage habits.