Rapid aerosol particle growth and increase of cloud condensationnucleus activity by secondary aerosol formation and condensation:A case study for regional air pollution in northeastern China

摘要

This study was part of the international field measurement Campaigns of Air QualityResearch in Beijing and Surrounding Region 2006 (CAREBeijing-2006). Weinvestigated a new particle formation event in a highly polluted air mass at a regional sitesouth of the megacity Beijing and its impact on the abundance and properties of cloudcondensation nuclei (CCN). During the 1-month observation, particle nucleation followedby significant particle growth on a regional scale was observed frequently (-30%), andwe chose 23 August 2006 as a representative case study. Secondary aerosol masswas produced continuously, with sulfate, ammonium, and oranics as major components.The aerosol mass growth rate was on average 19 μg m~(-3)h~(-1)during the late hours of theday. This growth rate was observed several times during the 1-month intensivemeasurements. The nucleation mode grew very quickly into the size range of CCN, andthe CCN size distribution was dominated by the growing nucleation mode (up to 80% ofthe total CCN number concentration) and not as usual by the accumulation mode. At watervapor supersaturations of 0.07-0.86%, the CCN number concentrations reachedmaximum values of 4000-19,000 cm~(-3)only 6-14 h after the nucleation event. Duringparticle formation and growth, the effective hygroscopicity parameter K increased fromabout 0.1-0.3 to 0.35-0.5 for particles with diameters of 40-90 nm, but it remainednearly constant at ~0.45 for particles with diameters of ~190 nm. This result is consistentwith aerosol chemical composition data, showing a pronounced increase of sulfate.