Pollution's color isn't uniform; it varies greatly depending on the type of pollutant and its concentration. Air pollution, for instance, is often depicted using a color-coded Air Quality Index (AQI).
Air Quality Index (AQI) Colors
The AQI uses colors to represent air quality levels:
- Green: Good air quality.
- Yellow: Moderate air quality.
- Orange: Unhealthy for sensitive groups.
- Red: Unhealthy.
- Purple: Very unhealthy.
- Maroon: Hazardous.
As noted in various sources, summer often sees more yellow, orange, and red AQI levels due to poorer air quality. Purple and maroon indicate the worst air quality, though maroon is rarely reached. AirNow.gov and the provided text both confirm this color-coded system.
Types of Pollution and Their Visual Appearance
Different pollutants have different appearances:
- Smog: Can appear reddish-brown (due to nitrogen oxides) or black/grey. Breeze Technologies
- Water pollution: Can manifest as discoloration, cloudiness, or the presence of algal blooms (often blue-green). Minnesota Pollution Control Agency
- Light pollution: While not a color itself, light pollution affects the night sky's appearance, making it brighter and less conducive to stargazing. Wiley Online Library
It is important to note that the color of pollution is not always visible to the naked eye; sophisticated instruments are often required for detection. For example, the presence of certain invisible gases contributes significantly to air pollution.
