Answer:
Decreasing amount of cloud in the sky
Explanation:
The earth's atmosphere is comprised of various gases and also there is the presence of water vapor, dust particles, and aerosols. The clouds containing water vapor creates a layer on the earth's atmosphere that affects the transparency of the atmosphere. The transparency of the earth's atmosphere is inversely proportional to the cloud covered in the sky. The absence of clouds in the sky provides a high transparency of the atmosphere.
Thus, transparency increases when there is a lesser cloud in the sky.