Condensation and coagulation sinks and formation of nucleation mode particles in coastal and boreal forest boundary layers

Abstract

The formation and growth of new particles has been evaluated using a revised version of a simple, but novel, theoretical tool. The concentration of condensable vapors and their source rates has been estimated using the aerosol condensation sink together with the measured particle growth rate. Also, by adding the coagulation sink and the measured formation rate of 3 nm particles, the formation rate of 1 nm particles and their concentration can be estimated. Condensation and coagulation sinks can be obtained from ambient aerosol size distribution data. The method has been applied to analyze the particle formation and growth rates observed during coastal and boreal forest nucleation events. The condensation sinks are typically 4–7 × 10−3 s−1 in the forest and 2 × 10−3 s−1 under coastal conditions, while the coagulation sinks for 1, 2, and 3 nm particles are typically smaller by factors 1.5–2, 5–7, and 11–15, respectively. The measured growth rates are 2–10 nm/h for the boreal forest and range from 15 to 180 nm/h at the coast, corresponding to a vapor concentration of 2–13 × 107 cm−3 and 108 cm−3 to 109 cm−3, respectively. The vapor source rate was 1–2 × 105 cm−3s−1 in the boreal forest and 2–5 × 106 cm−3s−1 in the coastal environment. The estimated formation rate of 1 nm particles in the forest environment was 8–20 cm−3s−1 and 300–10,000 cm−3s−1 at the coast. The concentration of 1 nm particles was estimated to be 2000–5000 and 4 × 104–7 × 106 particles cm−3 in forest and at coast, respectively.