Seminário do Departamento de Ciências Atmosféricas: "Atmospheric black carbon: Towards traceable absorption and mass concentration measurements"

Seminário do Departamento de Ciências Atmosféricas

Tema: Atmospheric black carbon: Towards traceable absorption and mass concentration measurements

Apresentação: Dr. Jorge Saturno (Physikalisch-Technische Bundesanstalt, Braunschweig / Germany)

Resumo:

Black carbon (BC) aerosol particles, produced by the incomplete combustion of carbonaceous fuels, absorb solar radiation, and exert a positive radiative forcing, thereby heating the atmosphere. To quantify this effect, radiative transfer models require knowledge of both the BC mass concentration and its light absorption, which are linked through the BC mass absorption cross-section (MAC). Freshly emitted BC has a MAC of 8 ± 1 m²/g at 550 nm, but this value can rise to as much as 15 m²/g at 550 nm as particles age and get coated, the so-called _lensing effect_. The influence of coatings and the evolution of MAC with ageing remain subjects of intense scientific discussion.

Measurements of BC light absorption and mass concentration are performed in both the lab and the field using a range of techniques. The most common absorption methods are filter-based attenuation measurements, while the most widely used mass method is thermo-optical analysis, which quantifies elemental carbon mass (EC; EN 16909:2017). Advances in both absorption and mass quantification techniques, offering improved accuracy and operational and scientific advantages, have led to more reliable field measurements, giving researchers a clearer picture of how atmospheric ageing and regional conditions affect the optical properties of BC.

In a recent study, we reviewed 63 publications reporting atmospheric MAC values and present the results in terms of aerosol type, measurement technique, regional variability, and how interpretation of results using these factors can help the community to use the appropriate MAC in models. We provide guidance and perspectives for future studies and how the literature on MAC can be exploited and interpreted in order to improve radiative models that include BC.

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