Volume 7, No. 4, December 2007, Pages 489-499 PDF(216 KB)
Homogeneous Ternary H2SO4–NH3–H2O Nucleation and Diesel Exhaust: a Classical Approach
Mikko Lemmetty1, Hanna Vehkamäki2, Annele Virtanen1, Markku Kulmala2, Jorma Keskinen1
1 Aerosol Physics Laboratory, Institute of Physics, Tampere University of Technology. P.O. Box 692, FIN-33101 Tampere, Finland
2 Division of Atmospheric Sciences, Department of Physical Sciences, University of Helsinki. P.O. Box 64, FIN-00014 University of Helsinki, Finland
The classical nucleation theory was used to model ternary nucleation at temperatures and concentrations observed in diluting diesel exhaust. The nucleation rate does not markedly depend on the NH3 concentration below the level of 0.8 ppb, with the binary H2O–H2SO4 mechanism dominating. This rules out the effect of dilution air ammonia levels on nucleation mode formation in most cases. On the other hand, with high NH3 concentration in the case of SCR (Selective Catalytic Reduction) technology, we predict a dependence between the ammonia slip and the nucleation mode concentration.
Ternary nucleation; Diesel exhaust; Ammonia slip; Aerosol emissions.