Simulation of Biogenic Aerosols in the Boreal Region and their Climatic Impact

Biogenic secondary organic aerosol (BSOA) constitutes a major fraction of aerosol over boreal forests. As the emissions of BSOA precursors are temperature dependent, changes in temperature are likely to have substantial implications on regional aerosol radiative forcing. In this work, we have used a century long aerosol-climate model simulation to investigate the effect of increasing temperature on organic aerosol mass loadings, and further on aerosol-cloud interaction. The analysis was based on a nudged simulation done with ECHAM6-SALSA covering the period from 1905 to 2010. We limited the analysis to summer months to isolate the temperature dependence of biogenic emissions from the seasonal cycle of vegetation growth. We concentrated on three regions in Russia and three in Canada to analyze the spatial variability of the climatic impacts of BSOA. Our analysis showed that BSOA loadings increased with surface temperature and higher BSOA loads were connected to higher cloud condensation nuclei concentrations in all the regions. However, the relationship between BSOA and cloud optical thickness or cloud droplet size was not that clear in all the regions. These regional differences highlight the need to have accurate aerosol and cloud observations from various locations in the boreal region in order to estimate the climatic significance of biogenic aerosols.