Soiling index is used to monitor:

Ans. (b) Air pollutionRef: Park 23rded. 1736Indicators of Air Pollution* Smoke or Soiling index: A known volume of air is filtered through a white filter paper under specified conditions and the stain is measured by photoelectric meter. Smoke concentration is estimated and expressed as micrograms/cubic metre of air as an average level over a period of time.* Sulphur dioxide This gas is a major contaminant in many urban and industrial areas. Its concentration is estimated in all air pollution surveys. So, it is the best indicator of air pollution* Grit and dust measurement: Deposit gauges collect grit, dust and other solids. There are analysed monthly.* Coefficient of haze: A factor used, particularly in the USA in assessing the amount of smoke or other aerosol in air.* Air pollution index: It is an arbitrary index which takes into account one or more pollutants as a measure of the severity of pollution