Optical Sensing of Black Carbon

Black carbon (BC), referring to soot aerosol containing primarily elemental carbon, absorbs radiation over a wide spectral range and is regarded among the most important atmospheric climate forcers, together with CO2 and methane. Compared to greenhouse gases, the net climate impact of BC has more uncertainty due to the complex optical and physical properties of particulate matter. In addition to its climate effects, BC belongs to the class of ultrafine particles, with particularly adverse health effects.

There has recently been growing interest in expanding the coverage of BC monitoring and on improving the standardization of its measurements. Conventionally, BC absorption is measured by monitoring the decrease in optical transmission of a filter where the aerosol is collected over time. However, the indirect nature of the method is detrimental to its accuracy. Methods that can be applied directly in the aerosol phase, typically based on photoacoustic spectroscopy, photothermal interferometry or simultaneous extinction and scattering measurements, have been proposed as alternatives or as calibration standards for the widely used filter-based methods.

In this webinar hosted by the Environmental Sensing Technical Group, Juho Karhu will introduce optical methods employed in BC monitoring and in optical absorption measurements of aerosols. A general overview will be followed by a more detailed look into recent demonstration of applying cantilever enhanced photoacoustic spectroscopy in BC monitoring.

Subject Matter Level: Intermediate - Assumes basic knowledge of the topic

What You Will Learn:
• A comprehensive look at how black carbon contributes to climate change and affects human health and environmental quality
• A comparison of traditional and advanced optical methods for measuring black carbon, including filter-based and aerosol-phase techniques
• Insights into the application of cantilever-enhanced photoacoustic spectroscopy

About the Presenter: Juho Karhu from University of Helsinki

Juho Karhu defended his PhD at the University of Helsinki laser spectroscopy group with a thesis on optical frequency comb assisted molecular spectroscopy. During a postdoc period at Aalto University, his work was focused on photoacoustic spectroscopy applied in sensing of gases and light absorbing aerosols, such as black carbon. In 2024 he received an Academy Research Fellowship at the University of Helsinki, to expand the photoacoustic sensing work to a wider range of atmospheric aerosols.