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Abstract
Abstract. The North China plain is a region with megacities and huge populations. Aerosols over the highly polluted area have a significant impact on the 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 high percentage of particles were sulfur-rich (47–49%). In phase-III, the haze disappeared due to the intrusion of cold air from the northwest, and mineral dust particles from deserts were dominant (43%). NPF followed by particle growth during daytime was more pronounced on hazy than on 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. However, the presence of fine anthropogenic particles (e.g., soot, metal, and fly ash) embedded within S-rich particles indicates that they could weaken NPF and enhance particle growth through condensation and coagulation. Abundant mineral particles in phase-III likely suppressed the NPF processes because they supplied sufficient area on which acidic gases or acids condensed.
Highlights
Atmospheric particles in the troposphere, especially submicron particles that have relatively long atmospheric residence times, can change the earth’s radiative balance through scattering and absorbing radiation (Charlson et al, 1992; IPCC, 2007)
Phase-III, crustal mineral particles (43 %) were a dominant constituent, and the rest consisted of metal (24 %), S-rich (19 %), Na/K-S/N (9 %), fly ash (3 %), and Ca-S/N (2 %)
Wu et al (2007) found that new particle formation (NPF) events were uncommon in the polluted area of northern China because of rather high concentrations of the pre-existing particles near the ground level. These results provide insights into regional NPF events, which can frequently occur at upper levels of the regional haze layers rather than near the surface layer in the North China plain (NCP)
Summary
Atmospheric particles in the troposphere, especially submicron particles that have relatively long atmospheric residence times, can change the earth’s radiative balance through scattering and absorbing radiation (Charlson et al, 1992; IPCC, 2007). Anthropogenic and natural perturbations of the radiation balance depend either directly or indirectly on several inherent properties of particles, including mass concentration, composition, and size distribution. The chemical composition of aerosols among various size ranges is a key factor in determining their hygroscopicity, ability of activation, and optical properties (Andreae and Rosenfeld, 2008; Hudson, 2007; Lohmann and Feichter, 2005). In the past two decades, rapidly industrializing East China has contributed massive quantities of anthropogenic pollutants into the troposphere because of inadequate pollution controls fostered by weak regulations (Fang et al, 2009; He et al, 2002; Lu et al, 2010).
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