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

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 PM<sub>2.5</sub> 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

Morphology, Composition, and Mixing State of Individual Aerosol Particles in Northeast China during Wintertime

“…In addition, these S-rich particles were internally mixed with primary OM particles at the T2 site (Figure 2b-d), thereby suggesting that OM particles become more aged during long-range transport. Compared with haze particles collected in the North China Plain, our study did not observe fly ash and metal, but more abundance of OM-dominated particles [23,24]. As a result, we can exclude regional contribution from emissions of heavy industries and coal-fired power plants in upwind areas.…”

Integrated evaluation of aerosols during haze-fog episodes at one regional background site in North China Plain

“…The growth processes can be enhanced by the internally mixed particles in haze layers (Li et al, 2011a). In addition, transmission electron microscopy (TEM) is an important technique for investigating the physical and chemical properties and mixing state of individual aerosol particles in HF episode (Li et al, 2011a;Posfai and Buseck, 2010;Ueda et al, 2011).…”

Mixing state of individual submicron carbon-containing particles during spring and fall seasons in urban Guangzhou, China: a case study

“…Similarly, Fu et al (2012) observed four types of carbonaceous aerosols in the Shanghai atmosphere, and found that most of the particles were coated with secondary organic aerosols. Based on transmission electron microscopy, Li et al (2011b) also found more fractions of internally mixed EC particles in the polluted air of northern China. Single-particle soot photometer measurements revealed that the number fraction of internally mixed EC was highly variable and could be as high as ∼ 70 % in the PRD region, while the detailed information on mixing state is limited by this instrument (Huang et al, 2011(Huang et al, , 2012.…”