Seminar

Abstract

Black carbon (BC) has received increasing attention as an important contributor to global warming and can impact climate through several mechanisms. BC aerosols are mainly hydrophobic upon emission and are removed by wet deposition. The particles then become more hygroscopic, i.e. aged, through interaction with water-soluble species such as sulfate and organic carbon, forming an internal mixture. The lifetime, and hence transport and distribution, as well as cloud nucleating and optical properties of BC depend on the mixing state of the particles, and the parameterization of aging is an important element of global aerosol modeling. A microphysical aerosol module (M7) has been implemented in the chemistry transport model OsloCTM2 to represent aerosol size distribution and interaction and the formation of mixed particles and has been compared to the original bulk parameterization of aerosols. While the microphysical module captures seasonal and regional variations in BC aging by accounting for coating of the particles by sulfate, a fixed transfer rate from hydrophobic to hygroscopic particles is applied in the bulk parameterization. This leads to differences in lifetime and distribution of BC in OsloCTM2 and to differences in the model performance compared to measurements. There are significant uncertainties related to the microphysics of BC, such as coating thickness, interaction of BC with organics and nitrate and wet removal processes, which will be explored. For validation of the model, the M7 microphysical module will also be compared to more measurements from surface stations and from aircraft campaigns with the Single Particle Soot Photometer.