Cantilever-enhanced Photoacoustic Instrument for Field Measurements of Black Carbon

Black carbon (BC), an aerosol emitted from biomass combustion and comprised mostly of elemental carbon, is one of the most harmful air pollutants in the world. Due to its ability to easily penetrate the lungs and strongly absorb solar radiation, BC plays a significant role in air quality and climate change [1], driving the growing demand for its reliable detection. Typical BC detectors are based on collecting a BC sample on a filter and measuring the change in the filter's optical transmission. However, this approach is hindered by the optical interference of the filter [2], and the change in particle morphology during the collection process. Photoacoustics is one of the more prevalent methods used to measure aerosol light absorption directly in the aerosol phase [3]. To overcome the limited sensitivity of conventional photoacoustic instruments, we have recently reported a new approach based on cantilever-enhanced photoacoustic spectroscopy (CEPAS) [4]. Our record-breaking sensitivity was achieved without any acoustic resonances, making the instrument robust and enabling effortless multi-wavelength operation, which is needed to distinguish BC from gaseous compounds that absorb visible light and from carbonaceous aerosols with a significant organic content, often referred as brown carbon.