Aerosol nucleation is an important source of particle number in theatmosphere. However, in order to become cloud condensation nuclei (CCN),freshly nucleated particles must undergo significant condensational growthwhile avoiding coagulational scavenging. In an effort to quantify thecontribution of nucleation to CCN, this work uses the GEOS-Chem-TOMAS globalaerosol model to calculate changes in CCN concentrations against a broadrange of nucleation rates and mechanisms. We then quantify the factors thatcontrol CCN formation from nucleation, including daily nucleation rates,growth rates, coagulation sinks, condensation sinks, survival probabilities,and CCN formation rates, in order to examine feedbacks that may limit growthof nucleated particles to CCN. Nucleation rate parameterizations tested inGEOS-Chem-TOMAS include ternary nucleation (with multiple tuning factors),activation nucleation (with two pre-factors), binary nucleation, andion-mediated nucleation. We find that nucleation makes a significantcontribution to boundary layer CCN(0.2%), but this contribution is onlymodestly sensitive to the choice of nucleation scheme, ranging from 49 to 78%increase in concentrations over a control simulation with no nucleation.Moreover, a two order-of-magnitude increase in the globally averagednucleation rate (via changes to tuning factors) results in small changes(less than 10%) to global CCN(0.2%) concentrations. To explain this,we present a simple theory showing that survival probability has anexponentially decreasing dependence on the square of the condensation sink.This functional form stems from a negative correlation between condensationsink and growth rate and a positive correlation between condensation sinkand coagulational scavenging. Conceptually, with a fixed condensable vaporbudget (sulfuric acid and organics), any increase in CCN concentrations dueto higher nucleation rates necessarily entails an increased aerosol surfacearea in the accumulation mode, resulting in a higher condensation sink, whichlowers vapor concentrations and growth rates. As a result, slowly growingnuclei are exposed to a higher frequency of coagulational scavenging for alonger period of time, thus reducing their survival probabilities andclosing a negative feedback loop that dampens the impact of nucleation onCCN. We confirm quantitatively that the decreases in survival probabilitypredicted by GEOS-Chem-TOMAS due to higher nucleation rates are inaccordance with this simple theory of survival probability.
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