'Ringelmann scale' is used to measure density of

The Ringelmann scale is a scheme for measuring the apparent density of smoke. It was developed by Maximilien Ringelmann of France in 1888. The scale consists of six levels (0 to 5), where 0 represents no smoke (white) and 5 represents 100% black smoke. The assessment is made by comparing the shade of the smoke emitted from a stack with a series of charts containing different intensities of black grids on a white background. It is a standard tool used in air pollution monitoring and environmental regulation to assess the opacity of particulate emissions from industrial chimneys and engines.