Cloud Condensation Nuclei Activity and Hygroscopicity of Fresh and Aged Biomass Burning Particles

Biomass burning particles are one of the largest aerosol sources worldwide and contribute a significant fraction of the global cloud condensation nuclei (CCN) burden. Chemical aging experiments of sawgrass burning particles took place in a smog chamber by turning on the UV light after HONO or H2O2 injection. The CCN activity and corresponding hygroscopicity of fresh and aged particles were measured. Most of the fresh particles can serve as reasonable CCN, and the average activation diameters at 0.2% supersaturation were 114-125nm in the experiments. The aging process caused that the mass fraction of organic aerosols decrease and condensed phase nitrate NO3- increase, and also the average atomic oxygen to carbon (O:C) ratios increase, which were the main reasons that the aged particles were more CCN active and hygroscopic. The average activation diameters decreased by 8-15% at 0.2% supersaturation after aging, and hygroscopic parameter increased by 30-42%. The chemical aging productions were a little different in experiments, but the CCN property and hygroscopicity change trends were quite similar.