<prompt> Soiling index used for -Water pollutionAir pollutionSound pollutionFaecal pollution  <response>: B Soiling index 683 - Park 22ndSmoke 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 microgramscubic meter of air as an average level over a period of time. Best indicators of air pollution are sulphurdioxide, smoke and suspended particle Source of carbon monoxide indoor air pollution is combustion equipment, stove, Gas heaters.AIR POLLUTION INDEX It is an arbitary index which takes into account one or more pollutants as a measure of the severity of pollution. For example, the following index has been used in USA: 10 times the sulphur dio-oxide concentration plus twice the carbon mono oxide concentration both in ppm by volume plus twice the coefficient of haze. It was considered to be a cause for alarm when the value of this index rose from its value of about 12 - 50 or more. 