Individual particle analysis of aerosols collected under haze and non-haze conditions at a high-elevation mountain site in the North China plain

摘要

The North China plain is a region with megacities and huge populations.Aerosols over the highly polluted area have a significant impact on theregional and global climate. In order to investigate the physical andchemical characteristics of aerosol particles in elevated layers there,observations were carried out at the summit of Mt. Tai (1534 m a.s.l.) from19 to 28 April, 2010, when the air masses were advected from the east(phase-I: 19–21 April), from the south (phase-II: 22–25 April), and from thenorthwest (phase-III: 26–28 April). Individual aerosol particles wereidentified with transmission electron microscopy (TEM), new particleformation (NPF) and growth events were monitored by a wide-range particlespectrometer, and ion concentrations in PM_2.5 were analyzed. Duringphase-I and phase-II, haze layers caused by anthropogenic pollution wereobserved, and a high percentage of particles were sulfur-rich (47–49%).In phase-III, the haze disappeared due to the intrusion of cold air from thenorthwest, and mineral dust particles from deserts were dominant (43%).NPF followed by particle growth during daytime was more pronounced on hazythan on clear days. Particle growth during daytime resulted in an increaseof particle geometric mean diameter from 10–22 nm in the morning to 56–96 nmin the evening. TEM analysis suggests that sulfuric acid and secondaryorganic compounds should be important factors for particle nucleation andgrowth. However, the presence of fine anthropogenic particles (e.g., soot,metal, and fly ash) embedded within S-rich particles indicates that theycould weaken NPF and enhance particle growth through condensation andcoagulation. Abundant mineral particles in phase-III likely suppressed theNPF processes because they supplied sufficient area on which acidic gases oracids condensed.