Séminaire Fengshan LIU
Black Carbon Metrology, Metrology Research Centre,
National Research Council, Ottawa, Ontario, Canada K1A 0R6
03 décembre 2018, 14:20, Amphithéatre du CERLA
Université de Lille, Faculté des Sciences et Technologies
Conférence donnée en ouverture de
la réunion annuelle du groupement de recherche SUIE (GDR SUIE)
The optical properties of black carbon particles and measurements of black carbon mass concentrations using optical methods
Black carbon (BC, also called soot in the combustion community) particles emitted from combustion systems and biomass burning have been recognized as the second largest man-made climate forcing factor on both local and global scales just after carbon dioxide and a significant risk for various ultrafine particle related diseases and fatalities.
To monitor BC mass concentration emitted from combustion devices and in the atmosphere, it is desirable to have accurate and real-time (with time response on the order of 1 s) measurement capabilities. Such requirements can only be met by optically based methods. Several optically based BC mass concentration commercial instruments have been commonly used, such as photoacoustic extinctiometer (PAX), cavity attenuated phase shift (CAPS) monitor, and Aethalomter. These optical instruments directly measure the optical properties of BC aerosols, such as the absorption and scattering coefficients or mean particle absorption and scattering cross sections. Then the measured absorption coefficient is converted to BC mass concentration with the help of mass absorption coefficient (MAC). The underlying assumption of this practice is that MAC of BC in the near infrared spectral region (typically about 600 to 900 nm) is robust and not influenced significantly by BC particle size and morphology. To assess the role of BC in climate forcing, it is necessary to predict the radiative properties of BC particles, which in turn requires the refractive index of BC.
In this presentation, recent experimental measurements and numerical predictions of MAC of freshly emitted BC are first reviewed. The effects of morphological parameters and refractive index on MAC of BC particles in the visible and near infrared spectra are then presented. A methodology is proposed to assess if an assumed refractive index is acceptable based on the measured MAC values in the aerosol community or the soot absorption function values in the combustion community.