On the formation, growth and composition of nucleation mode particles

Taking advantage of only the measured aerosol particles spectral evolution as a function of time, a new analytical tool is developed to derive formati on and growth properties of nucleation mode aerosols. This method, when use d with hygroscopic growth-factors, can also estimate basic composition prop erties of these recently-formed particles. From size spectra the diameter g rowth-rate can be obtained, and aerosol condensation and coagulation sinks can be calculated. Using this growth-rate and condensation sink, the concen tration of condensable vapours and their source rate can be estimated. Then , combining the coagulation sink together with measured number concentratio ns and apparent source rates of 3 run particles, I nm particle nucleation r ates and concentration can be estimated. To estimate nucleation rates and v apour concentration source rates producing new particle bursts over the Bor eal forest regions, three cases from the BIOFOR project were examined using this analytical tool. In this environment, the nucleation mode growth-rate was observed to be 2-3 nm hour(-1), which required a condensable vapour co ncentration of 2.5-4 x 10(7) cm(-3) and a source rate of approximately 7.5- 11 x 10(4) cm(-3) s(-1) to be sustained. The formation rate of 3 nm particl es was approximate to 1 particle cm(-)3 s(-1) in all three cases. The estim ated formation rate of 1 nm particles was 10-100 particles cm(-3) s(-1), wh ile their concentration was estimated to be between 10,000 and 100,000 part icles cm(-3). Using hygroscopicity data and mass flux expressions, the mass flux of insoluble vapour is estimated to be of the same order of magnitude as that of soluble vapour, with a soluble to insoluble vapour flux ratio r anging from 0.7 to 1.4 during these nucleation events.