The terms Elemental Carbon (EC) and Black Carbon (BC) are both used to describe the product of incomplete combustion of fossil fuels, biomass, and biofuels, which is a significant component of aerosols (airborne particulate matter). While often used interchangeably in general discussion, they represent distinct concepts primarily tied to their respective measurement methodologies. Understanding this difference is crucial in air quality monitoring, climate science, and health studies.

Elemental Carbon (EC): The Reference Method

Elemental Carbon (EC) is the term associated with the reference method for measuring this specific fraction of carbonaceous aerosol.

• Measurement Method: EC is quantified using thermal-optical analysis. This technique relies on the sequential heating of a filter sample to different temperatures in different atmospheres (non-oxidizing and oxidizing) to distinguish carbon fractions.
• Standard Protocol: The EN 16909 standard is a prominent European standard for the determination of EC (and Organic Carbon, OC) in ambient air, often employing the thermal-optical reference technique.
• Specific Protocol: The EUSAAR_2 thermal protocol is a common, specific thermal-optical protocol used to define the temperature steps and atmospheres for the measurement.
• Charring Correction: A critical part of the thermal-optical method is the charring correction, typically based on the transmittance (or reflectance) of a laser beam through the filter. This corrects for the formation of “pyrolyzed” or “charred” organic carbon during the heating process, which can otherwise be misclassified as EC.
• Definition: Conceptually, EC represents the carbon in its pure, elemental form—the refractory, graphitic, or amorphous carbon that is the most stable at high temperatures.

Black Carbon (BC): The Equivalent Method

Black Carbon (BC) is the equivalent term used to describe this carbon fraction when measured using methods that rely on the particle’s light-absorbing properties.

Equivalence: Because the measured light absorption is highly correlated with the mass of the pure elemental carbon fraction, BC is considered the equivalent method to measure this carbon component. However, the result is dependent on the MAC value used in the calculation, which can vary depending on particle morphology and mixing state.

Measurement Method: BC is quantified using Filter Absorption Photometers (FAPs). These instruments measure the light attenuation or absorption by the particles collected on a filter. Common FAP instruments include the Aethalometer and the Multi-Angle Absorption Photometer (MAAP).

Measurement Principle: FAPs measure the particle light absorption coefficient (αap​), which is the amount of light absorbed by particles in an aerosol. This measurement is then converted to a mass concentration of BC by assuming a fixed mass absorption cross-section (MAC).

Core Assumption: The measurement relies on the fundamental assumption that BC is the unique absorbing species within the aerosol. This means any measured light absorption is entirely attributed to BC mass.