Bremen 2017 – scientific programme

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UP: Fachverband Umweltphysik

UP 19: Symposium Einfluss solarer Variabilität auf Atmosphäre und Klima der Erde: Von der Heliophysik bis zur Erdatmosphäre

UP 19.3: Invited Talk

Friday, March 17, 2017, 09:30–10:00, GW2 B2880

Impact of precursor gases and ions on new particle formation and climate — •Urs Baltensperger — Paul Scherrer Institute, Villigen, Switzerland

Globally, a significant source of cloud condensation nuclei for cloud formation is thought to originate from new particle formation (aerosol nucleation). With the CLOUD collaboration we investigated the role of nucleating substances such as gaseous sulfuric acid, ammonia, water vapor as well as of ions, produced e.g. by galactic cosmic rays. Using the results in a global model we showed that nearly all nucleation throughout the present-day atmosphere involves ammonia or biogenic organic compounds, in addition to sulfuric acid. A considerable fraction of nucleation involves ions, but the relatively weak dependence on ion concentrations indicates that for the processes studied, variations in cosmic ray intensity do not appreciably affect climate through nucleation in the present-day atmosphere. Recently, we could also show that highly oxygenated molecules (HOMs) produced by the oxidation of biogenic precursors are able to trigger new particle formation on their own, even in the absence of sulfuric acid. We confirmed that this mechanism does occur in today*s lower free troposphere. We also show that this mechanism was important for the formation of additional new particles and cloud condensation nuclei in the preindustrial atmosphere, when sulfur dioxide emissions were substantially lower. This reduces the magnitude of the annual global mean radiative forcing caused by changes of cloud albedo, which implies a reduced climate sensitivity.