A New Life for Black Smoke as Proxy for Elemental Carbon, But Without Iso-9835

Abstract

Black Smoke serves as official measure for Particulate Matter (PM) because of its easy determination via the blackness of filter samples.  However, this implies that BS is a poor proxy for total PM but rather a good equivalence quantity for the light absorbing elemental carbon (EC), as we showed in a recent study [ten Brink et al., 2024]. We strongly argue here for a new life for BS as measure for EC in the framework of a recommendation in the latest WHO-report on Air Quality for monitoring EC as proxy for diesel soot. In the countries where BS is measured, expensive EC (or black carbon, BC) monitoring equipment is absent, but BS data could be converted to EC mass concentration with our equivalency factor of 0.16 +- 25% with EC as if measured according to the standard EUSAAR2-TOT protocol in the EU. Yet there is a caveat; national regulations demand the use of the protocol for measurement given in ISO-report 9835. We critically analysed this report and found a series of critical issues. It only mentions a dimensionless “Black Smoke Index”, whereas in official legislation BS must be provided as a mass concentration in the standard unit of µg m-3. In addition there is no reference for the conversion of the light absorption to BSI; in fact the report does not even provide a proper definition of BS. Therefore we strongly argue for the use of the official manual by Christolis et al. [1992] for conversion of light absorption measured from filter deposits to a mass concentration of BS and use the equivalency factor we obtained to convert BS to EC.

Keywords: Black Smoke, Elemental Carbon, ISO-9835, WHO Air-Quality Report