Theoretical constraints on pure vapor-pressure driven condensation of organics to ultrafine particles

[1] Organic condensation to freshly nucleated particles contributes substantially to their growth. Here we explore a range of constraints on this process, under the assumption that gas-phase oxidation of organic vapors by hydroxy radical is forming organics with a sufficiently low volatility to condense onto particles in the 2–20 nm size range. To condense but not homogeneously nucleate, vapors need to have saturation concentrations (C*) in the 10−3 − 10−2μg m−3 range, and this is exactly the range that gas-phase chemistry is likely to produce. At least half of the observed growth rate of ultrafine particles can be explained by these simple considerations and constraints.