Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 9 20 2009 10.5194/acp-9-7913-2009 http://www.atmos-chem-phys.net/9/7913/2009/ http://www.atmos-chem-phys.net/9/7913/2009/acp-9-7913-2009.html http://www.atmos-chem-phys.net/9/7913/2009/acp-9-7913-2009.pdf 7913 7922 2009-10-22 Kinetic modeling of nucleation experiments involving SO₂ and OH: new insights into the underlying nucleation mechanisms H. Du huadu@asrc.cestm.albany.edu F. Yu Atmospheric Sciences Research Center State University of New York at Albany, Albany, NY, 12203, USA Nucleation is an important source of atmospheric aerosols which have significant climatic and health implications. Despite intensive theoretical and field studies over the past decades, the dominant nucleation mechanism in the lower troposphere remains to be mysterious. Several recent laboratory studies on atmospheric nucleation may shed light on this important problem. However, the most interesting finding from those studies was based on the derived H₂SO₄ concentration whose accuracy has not yet been evaluated by any other means. Moreover, the threshold H₂SO₄ concentration needed to reach the same degree of nucleation reported by two separate nucleation studies varies by about one order of magnitude. In this study, we apply a recently updated kinetic nucleation model to study the nucleation phenomena observed in those recent experiments. We show that the H₂SO₄ concentration can be estimated with a higher level of accuracy with the kinetic model by constraining the simulated particle size distributions with observed ones. We find that the required H₂SO₄ concentrations to achieve the best agreement between modeling and measurements are a factor of ~2 to 4 higher than reported in those experiments. 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