Once a dark red color appears during urban sunsets, it indicates poor air quality. Why is that?
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There is a question in the \"One Question per Day\" series that goes like this: when the city’s sunset takes on a dark red color, it serves as a warning to us – today’s air quality is extremely poor! Why? ? ?
The scattering effect of red light is very noticeable; the more suspended particles there are in the air, the stronger this scattering effect becomes. Since red light has a longer wavelength, this indicates that there are many suspended particles in the air, meaning the air quality is not good. In fact, sunset hues are also formed by the scattering of suspended particles in the atmosphere, but they are caused by water vapor (clouds, fog); during this scattering process refraction occurs as well, resulting in light that appears yellow with a red tint.
In a highly industrialized area, the color of the sky is completely different when pollutants are suspended in the air as particles. The round sun had an orange-red color, while the sky was a dark red. The differences in red intensity reflect the thickness of the pollutants. Sometimes, after sunset, two wide bands of color appear in the sky on either side; near the horizon it is dark red, while above that it is dark blue. Pollutant particles indicate their presence through subtle changes in the colorful hues of the sky. Once the urban sunset turns dark red, it is a warning to us.