How many rectangular charts are in the Ringlemann smoke chart in the United States?

The Ringlemann smoke chart is a standardized tool used to visually estimate the density of smoke emissions. In the context of the United States, the chart consists of four rectangular patches that represent varying levels of smoke opacity. Each of these rectangles corresponds to a different category of smoke density, ranging from a very light smoke (barely visible) to a dark, heavy smoke.

The four rectangles provide a clear and structured method for observers to assess and categorize smoke as it is emitted from various sources, such as industrial facilities or residential heating. This classification aids in understanding pollution levels and compliance with air quality regulations. The design of the chart allows for quick visual assessment, making it a practical tool for environmental monitoring and regulation enforcement. The four distinct rectangles serve as a reference point to ensure consistency in smoke observation and reporting across different scenarios.