Derivation of Antarctic stratospheric sulfuric acid profiles and nucleation modeling of the polar stratospheric CN layer

• Main Authors: Münch, Steffen, Curtius, Joachim
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: ddc:550; Antarctic; Arctic; The Antarctic; Antarc*
• Online Access: http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/43818; https://nbn-resolving.org/urn:nbn:de:hebis:30:3-438182; https://doi.org/10.5194/acp-2016-583; http://publikationen.ub.uni-frankfurt.de/files/43818/acp-2016-583.pdf

Recent analysis of long-term balloon-borne measurements of Antarctic stratospheric condensation nuclei (CN) and temperature combined with global model calculations showed the wide extent of a mid stratospheric layer of new particles. Here the nucleation model SAWNUC is used to derive Antarctic stratospheric gaseous sulfuric acid profiles and to investigate the nucleation process of this CN layer. The sulfuric acid profiles were derived for an altitude range of 18-32 km between July and October by simulating air parcel trajectories that descend inside the polar vortex and calculating the sulfuric acid amount that reproduces the observations. The derived sulfuric acid concentrations (volume mixing ratios) are of the order of magnitude of 104 cm-3 (10-14) in July. In the following months the concentrations increase to about 107 cm-3 (10 exp -11) in October. They depend strongly on the temperature because a given temperature leaves only a small sulfuric acid range to reproduce the observed magnitude of CN. Ion-induced nucleation occurs. However, while it dominates nucleation at higher temperatures it has no significant influence on the nucleation rates at lower temperatures. Preexisting particles significantly reduce nucleation at sulfuric acid mixing ratios below 1 ppt. First estimates of sulfuric acid production rates range from 0.5 to about 500 molecules cm-3 s-1. A production mechanism for gaseous sulfuric acid during the Antarctic winter seems to be necessary to fully explain the observations. The derived sulfuric acid profiles compare well with midlatitude and Arctic sulfuric acid concentrations.