A new source of tropospheric aerosols: Ion-ion recombination

Abstract

We propose a new source of aerosol particles in the lower atmosphere that is based on the formation, growth, and recombination of ubiquitous cosmogenically-generated ions. This mechanism provides a uniform, continuous fine-particle generator in the presence of precursor vapors, such as sulfuric acid, or certain organic compounds. Thus, for example, aqueous sulfate aerosols can form at sulfuric acid vapor partial pressures well below the supersaturations required for homogeneous nucleation. Detailed microphysical modeling shows that the highly nonlinear chemical/physical system comprising ions, vapors, and aerosols produces ultrafine and accumulation mode particles having characteristics similar to those detected in the lower troposphere. Accordingly, this mechanism may explain the presence of a stable boundary layer aerosol population of several hundred particles/cm3. The theory of nucleation by ion-ion recombination (NIIR) is roughly calibrated here using observed ultrafine particle measurements, and is applied to interpret tropospheric aerosol observations.