Interactions of Flame-Generated Incipient Nanoparticles with Water

We experimentally examined the Cloud Condensation Nuclei (CCN) forming potential of Organic Carbon (OC) nanoparticles formed in non-sooting premixed flames. Flame-generated particles were grown by coagulation, and the fraction of particles that grow in a humid environment was measured as a function of dry particle size. A differential mobility analyzer is used select particles of a particular size, and their total concentration as well as the concentration of only those particles that grow in a humid environment (S=0.8) was measured simultaneously. Flame-generated particles in the size range 30-60 nm did not grow to droplets larger than 300nm. For NaCl particles produced by electrospray, also tested in the same conditions, half grew by condensation for dry particles with a diameter of 28 nm, in good agreement with earlier works, validating our experimental approach. While the results are preliminary, they suggest that freshly emitted OC nanoparticles are unlikely to act as CCN. Future work should examine larger flame-generated particles exposed to humid environments with higher S and how atmospheric transformations by oxidization and UV radiation affect the CCN-forming potential of combustion-generated OC nanoparticles.