Reduced effective radiative forcing from cloud–aerosol interactions (ERF aci ) with improved treatment of early aerosol growth in an Earth system model

• Published in: Atmospheric chemistry and physics 2021-11, Vol.21 (23), p.17243-17265
• Main Authors: Blichner, Sara Marie, Sporre, Moa Kristina, Berntsen, Terje Koren
• Format: Article
• Language: English
• Subjects: Aerosol concentrations; Aerosol-cloud interactions; Aerosols; Air masses; Air pollution; Analysis; Anthropogenic factors; Atmosphere; Atmospheric aerosols; Atmospheric carbon dioxide; Atmospheric conditions; Atmospheric models; Climate change; Cloud condensation nuclei; Cloud droplets; Clouds; Coagulation; Condensation; Condensation nuclei; Droplets; Earth and Related Environmental Sciences; Emissions; Geovetenskap och miljövetenskap; Greenhouse effect; Greenhouse gases; Growth; Hygroscopicity; Meteorologi och atmosfärforskning; Meteorology and Atmospheric Sciences; Natural Sciences; Naturvetenskap; Nucleation; Particle formation; Radiation; Radiative forcing; Regions; Secondary aerosols; Simulation; Sulfates
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-21-17243-2021

Historically, aerosols of anthropogenic origin have offset some of the warming from increased atmospheric greenhouse gas concentrations. The strength of this negative aerosol forcing, however, is highly uncertain - especially the part originating from cloud-aerosol interactions. An important part of this uncertainty originates from our lack of knowledge about pre-industrial aerosols and how many of these would have acted as cloud condensation nuclei (CCN). In order to simulate CCN concentrations in models, we must adequately model secondary aerosols, including new particle formation (NPF) and early growth, which contributes a large part of atmospheric CCN. In this study, we investigate the effective radiative forcing (ERF) from cloud-aerosol interactions (ERF.sub.aci) with an improved treatment of early particle growth, as presented in Blichner et al. (2021). We compare the improved scheme to the default scheme, OsloAero, which are both embedded in the atmospheric component of the Norwegian Earth System Model v2 (NorESM2). The improved scheme, OsloAeroSec, includes a sectional scheme that treats the growth of particles from 5-39.6 nm in diameter, which thereafter inputs the particles to the smallest mode in the pre-existing modal aerosol scheme. The default scheme parameterizes the growth of particles from nucleation up to the smallest mode, a process that can take several hours. The explicit treatment of early growth in OsloAeroSec, on the other hand, captures the changes in atmospheric conditions during this growth time in terms of air mass mixing, transport, and condensation and coagulation.