Measurement of Model Aerosols Containing Two Metal Components Formed via Cooling and Dilution Routes

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The emission of alkali and heavy metals in combustion processes is an important contributor to environmental load. However, little is known of the mechanism by which gas-to-particle conversion occurs during cooling and dilution with the atmosphere at the exit of stacks. In the present work, particles generated from model exhaust gases derived from NaCl and CdCl2 were investigated experimentally in the laboratory. An on-line, gas-phase measurement system showed that the mean diameters of aerosol particles in single-metal evaporation of NaCl and CdCl2 were 35 and 30 nm, respectively, when the dilution ratio of the model gas was 1:20. However, the value was 50 nm in two-metal co-evaporation of NaCl with CdCl2 at the same dilution ratio. FE-SEM images of aerosol particles collected with a quartz fiber filter in the two-metal system showed a morphology similar to that of NaCl. It is thus concluded that Cd-containing vapors nucleate at and grow on the surface of NaCl particles. These results may be informative for predicting phenomena related to gas-to-particle conversion at the exit of stationary emission sources, from which such condensed particles are suspected to be released into the atmosphere.