Standard Black Smoke data in developing countries as (a first) proxy for "Elemental Carbon"

Area of Science:

• Environmental Science
• Analytical Chemistry
• Air Quality Monitoring

Background:

• Black Smoke (BS) is widely used in several countries for Particulate Matter (PM) monitoring due to its simple determination from filter paper blackness.
• While a poor indicator of total PM, BS serves as a reasonable proxy for light-absorbing Elemental Carbon (EC), particularly from diesel emissions.
• The World Health Organization (WHO) recommends EC monitoring, but lacks a prescribed measurement method, making the inexpensive BS method a viable option where direct EC analysis is costly or inaccessible.

Purpose of the Study:

• To critically evaluate the ISO-9835 protocol for Black Smoke (BS) measurement and its suitability for determining Elemental Carbon (EC).
• To propose an alternative, reliable method for BS determination and its conversion to EC concentrations, aligning with current air quality monitoring recommendations.
• To provide guidance for countries still employing BS measurements, ensuring data comparability with established EC monitoring protocols.

Main Methods:

• Analysis of the ISO-9835 protocol, identifying discrepancies between its dimensionless Black Smoke Index (BSI) and the legally required mass concentration (μg m⁻³).
• Evaluation of the lack of a defined conversion factor from light absorbance to BSI within the ISO-9835 standard.
• Recommendation and description of the EU-manual (Christolis et al., 1992) for BS determination using the EEL 43 Smoke Stain Reflectometer on Whatman-1 filters.

Main Results:

• The ISO-9835 protocol contains critical issues, including the absence of a proper definition for BS and a reference for converting optical reflectance to a BSI.
• The EU-manual provides a standardized method for BS measurement, enabling conversion of light absorption to mass concentration.
• A provisional conversion factor (0.15 ± 25%) from BS to EC, established by ten Brink et al. (2021), allows data to be aligned with the EUSAAR2-TOT protocol (EN 16909:2017).

Conclusions:

• The ISO-9835 protocol is inadequate for current air quality monitoring standards regarding BS and EC.
• Adoption of the EU-manual for BS determination is recommended for countries where this method is still in use.
• Provisional conversion of BS to EC using the factor of 0.15 ± 25% offers a cost-effective interim solution for EC monitoring until local equivalency is established.