Characterization of coated soot particles - Validating a new APM software and using it to design aerosol measurement set-ups

Abstract: Soot characteristics such as absorbing light are heavily dependent on its structure and interaction with other compounds. By coating soot or collapsing the soot core, the characteristics will be altered which affects its climate forcing, the lung deposition and other interactions with the human upper airways. In this work a new approach to measure aerosol particle mass with the Aerosol Particle Mass analyser (APM) was analysed and validated. A set-up was designed to coat soot particles with well-defined coating levels under controlled conditions. The new approach was used to prove restructuring of the soot core when coated by a hygroscopic compound and exposed to high relative humidity. Experiments were made with a Potential Aerosol Mass (PAM) chamber to simulate atmospheric aging of soot with the precursor alpha-pinene showing promising results of the combination PAM-APM. Black carbon (BC) being the second most important climate forcer makes it crucial to map out its atmospheric interactions for future climate research. By applying coating to soot the absorption rate of light can increase with 100% since the coating works as a lens focusing the light into the black soot core. Black carbon being associated with PM2.5 is linked to decreased lung function, increased respiratory symptoms and cardiopulmonary diseases.