Tropospheric sulfate aerosol formation via ion-ion recombination

We propose a source of aerosols in the lower atmosphere associated with the creation, growth, and recombination of ubiquitous cosmogenically generated ions. This particle source should be favorable in the relatively clean, st able marine boundary layer, providing a uniform, continuous fine particle g enerator in the presence of dimethylsulfide emissions. Through this mechani sm, new sulfate aerosols can be formed at sulfuric acid vapor partial press ures well below the supersaturations required for homogeneous binary nuclea tion of sulfuric acid/water solutions, which is consistent with numerous ob servations of new particle formation under sub-saturated conditions. The ev olving aerosols in turn control the acid vapor concentration and thus modul ate the sizes of the precursor ions and the rate of new particle formation. A simple model representing this nonlinear coupled system predicts that th e physical and chemical processes connecting ions, vapors, and aerosols eff ectively constrain the particle population to a relatively narrow range of values. This self-limiting behavior may explain in part the apparent stabil ity of the marine sulfate aerosol, with mean concentrations of the order of several hundred per cubic centimeter.