Science & Nature - Haze: how airborne particles obscure the summer sky

Haze is an atmospheric phenomenon where dry particulates like dust and smoke obscure visibility. In meteorology, haze often refers to wet aerosols suspended in the air. These form through complex chemical reactions when sulfur dioxide emissions transform into droplets of sulfuric acid, which is enhanced by sunlight and high humidity. Because these reactions require warm, calm conditions, wet haze is primarily a summer phenomenon. These aerosol veils can spread across thousands of kilometers, altering the sky's appearance from brownish to bluish.

Source: Wikipedia