Individual particle analysis of aerosols collected under haze and non-haze conditions at a high-elevation mountain site in the North China plain
1Environment Research Institute, Shandong University, Jinan, Shandong 250100, China
2State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Beijing 100083, China
3Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, Kumamoto 862–8502, Japan
Abstract. The North China plain is a region with megacities and huge populations. Aerosols over the highly polluted area have a significant impact on a regional and global climate. In order to investigate the physical and chemical characteristics of aerosol particles in elevated layers there, observations were carried out at the summit of Mt. Tai (1534 m a.s.l) from 19 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 the northwest (phase-III: 26–28 April). Individual aerosol particles were identified with transmission electron microscopy (TEM), new particle formation (NPF) and growth events were monitored by a wide-range particle spectrometer, and ion concentrations in PM2.5 were analyzed. During phase-I and phase-II, haze layers caused by anthropogenic pollution were observed, and a major number of particles were sulfur-rich (47–49 %). In phase-III, haze disappeared due to the intrusion of cold air from the northwest, and mineral dust particles from deserts were predominant (43 %). NPF followed by particle growth during daytime was more pronounced at upper levels of the haze layers than clear days. Particle growth during daytime resulted in an increase of particle geometric mean diameter from 10–22 nm in the morning to 56–96 nm in the evening. TEM analysis suggests that sulfuric acid and secondary organic compounds should be important factors for particle nucleation and growth. Moreover, the presence of ultrafine and fine anthropogenic particles (e.g., soot, metal, and fly ash) embedded within S-rich particles may indicate their influences on particle nucleation through condensation and enhancement of particle growth through coagulation. Each fine refractory particle can enlarge the sulfate particles by 10–20 nm. Abundant mineral particles in phase-III likely suppressed the NPF processes because a high number of crustal mineral particles in the free troposphere supplied an important surface on which acidic gases or acids condensed.