Hill Cap Cloud Thuringia 2010 (HCCT-2010): A ground-based integrated study of chemical aerosol-cloud interaction
Final Report Abstract
HCCT-2010 yielded a novel and complex dataset on aerosol cloud interactions. A good number of cloud events with appropriate meteorological conditions for a connected airflow between the three measurement sites was obtained. Many different instruments sampled a wealth of physical and chemical data, which is currently still being analysed under various aspects. One of the first highlights was the detection of a stronger hygroscopic growth of aerosol particles after the cloud passage. Another important finding of the HCCT-2010 campaign, which is published in Science, represents the exposure of an enhanced role of the transition metal ion chemistry for the catalysed in-cloud oxidation of S02. This result has strong implications for current estimations direct/indirect climatic effect in particular for estimates of the magnitude and spatial distribution of aerosol forcing. Furthermore, performed summit site FAGE measurements on in-cloud concentrations of OH and HO2 have provided for the first time the experimental evidence for the reduction of in-cloud gas phase HO2 concentrations larger than reduction of j(O1D). This direct physico-chemical interaction of clouds on HO2 etc. modifies the oxidation capacity of the atmosphere. This cloud interaction effect on the atmospheric oxidation capacity is huge importance for the cleaning capability of the atmosphere including the tropospheric lifetime and production of other air pollutants. However, this cloud chemistry effect is currently not yet represented global climate models, but will have a significant impact on air pollution and chemical weather/climate predictions. Overall, it is also noted that the obtained HCCT-2010 dataset is also the basis for extensive local parcel modelling of certain time periods during the campaign. At present, parcel model simulation results revealed interesting findings on the effects of clouds on tropospheric oxidants such as OH, HO2 and H2O2, and the chemical pro-cessing/partitioning of organic compounds inside and after the cloud passage. Furthermore, performed model studies supports the general interpretation of the obtained measured data. On other hand, the huge HCCT-2010 data set provides the possibility to evaluate current multiphase chemistry mechanisms and associated models.
