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 H 2 O 2 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 114–125 nm in the experiments. The aging process caused that the mass fraction of organic aerosols decrease and condensed phase nitrate NO 3 − 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 κ 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.