AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Evaluation of the Sectional Aerosol Model SALSA within the Aerosol-Climate Model ECHAM5-HAM
TOMMI BERGMAN, Veli-Matti Kerminen, Hannele Korhonen, Kari Lehtinen, Risto Makkonen, Antti Arola, Tero Mielonen, Sami Romakkaniemi, Markku Kulmala, Harri Kokkola, Finnish Meteorological Institute
Abstract Number: 164 Working Group: Aerosols, Clouds, and Climate
Abstract Aerosols affect the radiative balance of the atmosphere directly by absorbing and scattering radiation and indirectly by altering the radiative properties of clouds. For estimating the changes and uncertainties in both direct and indirect effect, the number size distribution shape and total particle number concentrations are the key parameters to predict.
Global climate models generally describe the aerosol size distribution with modal or moment approaches. However, sectional models enable more flexibility in describing the aerosol size distribution and the particle size dependent chemical composition, which have implications in e.g. aerosols' ability to form cloud droplets.
We present the implementation of the sectional aerosol model SALSA (Sectional Aerosol module for Large Scale Applications) (Bergman et al. 2011, Kokkola et al. 2008) within the ECHAM5-HAM aerosol-climate model. The SALSA module describes the aerosol population from 3 nano-meter to 10 micro-meter with 10 size classes with parallel chemical compositions, thereby consisting of 20 sections in total. The SALSA considers five compounds: sulphate, organic carbon, black carbon, sea salt and dust. In addition to these compounds the water uptake is also included.
The average modeled surface concentrations of sulphate, organic carbon and black carbon at the IMPROVE sites are within a factor fo two of the observations, with the mean fractional bias showing underestimation of 19-25 %. The simulated number size distributions show concentrations lower than observed at continental sites. This suggests that the new particle formation and condensational growth is too low and should be improved with a condensable vapour e.g. organic vapour. Over the tropical oceans the aerosol optical depth (AOD) shows good agreement with satellite retrievals, while at high latitudes and very polluted regions the AOD is underestimated. Nevertheless, our study shows that even very few sections is enough to simulate the aerosol population in the global scale.