Aerosol formation processes need more detailed descriptions in climate models

In his dissertation work, MSc Tommi Bergman explored the modeling of aerosols within global climate models. Since aerosols cause the highest uncertainty in radiative forcing, their accurate description in climate models is very important.

Aerosol description in aerosol-climate model ECHAM-HAMMOZ

Climate models often describe aerosols using simple mathematical functions, which are not well equipped to simulate the particle growth accurately. The thesis work compared the aerosol dynamics model SALSA (Sectional Aerosol model for Large Scale Applications) developed at the Finnish Meteorological institute to other descriptions employed within aerosol-climate models. The model was found to improve the simulation of aerosol size distribution and radiation interaction in the Tropical regions, while otherwise corresponding to traditional modal model.

International AeroCom-intercomparisons

Thesis work found that annual-mean particle concentrations correspond to observation adequately, but seasonal variation needs to be improved. However, an accurate view of the models' representation at a global level is challenging due to spatially limited observations. Most significant variation between the models was found in remote regions, especially the marine region around the Antarctica.

The dominant reasons for deficiencies in the remote regions are inadequately known formation mechanisms and poorly represented ageing of long-range transported aerosols. Particularly the particulate marine organic material is included only in a few models and requires further research.

New particle formation and emission mechanisms

Atmospheric aerosols are lifted from land and ocean surfaces by winds or are formed when sulphuric acid and other trace gases react. The spatial distribution and effects on climate of both emissions and formation of particles were studied in the thesis work.

Marine organic particles were found to increase significantly the aerosol radiative effect, although their simulated mass was found to be too low when compared against observations.

A mathematical model of amine-enhanced particle formation mechanism was developed and it was used to study the particle formation in a global climate model. Although the mathematical model reproduced the laboratory observations well, the formation rates were found to be too high in the climate model. The amine-enhanced nucleation was limited to the source regions of amine. This suggests that the influence of trace gases involved in the formation process must be taken explicitly into account when developing particle formation models for use in climate models.

Dissertation of Master of Science Tommi Bergman entitled Development and validation of Climate models: Towards a more detailed aerosol description was examined at the Faculty of Science and Forestry on Friday 4th December 2015. The opponent in the public examination was Dr. Claudia Timmreck, Max Planck Institute for Meteorology and the custos was Docent Harri Kokkola, Finnish Meteorological Institute.

Further information

Researcher Tommi Bergman, Finnish Meteorological Institute, tsrif nts ame ΑΤΤ_fm .i fi , tel. +358 295 392 084

Published: 28.12.2015
Categories: Events, Research

Original press release