Transmission electron microscopy study of aerosol particles from the brown hazes in northern China

Abstract

Airborne aerosol collections were performed in urban areas of Beijing that were affected by regional brown haze episodes over northern China from 31 May to 12 June 2007. Morphologies, elemental compositions, and mixing states of 810 individual aerosol particles of different sizes were obtained by transmission electron microscopy coupled with energy‐dispersive X‐ray spectrometry. The phases of some particles were verified using selected‐area electron diffraction. Aerosol particle types less than 10 μm in diameter include mineral, complex secondary (Ca‐S, K‐, and S‐rich), organic, soot, fly ash, and metal (Fe‐rich and Zn‐bearing). Most soot, fly ash, and organic particles are less than 2 μm in diameter. Approximately 84% of the analyzed mineral particles have diameters between 2 and 10 μm, while 81% of the analyzed complex secondary and metal particles are much smaller, from 0.1 to 2 μm. Trajectory analysis with fire maps show that southerly air masses arriving at Beijing have been transported through many agricultural biomass burning sites and heavy industrial areas. Spherical fly ash and Fe‐rich particles were from industrial emissions, and abundant K‐rich and organic particles likely originated from field burning of crop residues. Abundant Zn‐bearing particles are associated with industrial activities and local waste incinerators. On the basis of the detailed analysis of 443 analyzed aerosol particles, about 70% of these particles are internally mixed with two or more aerosol components from different sources. Most mineral particles are covered with visible coatings that contain N, O, Ca (or Mg), minor S, and Cl. K‐ and S‐rich particles tend to be coagulated with fly ash, soot, metal, and fine‐grained mineral particles. Organic materials internally mixed with K‐ and S‐rich particles can be their inclusions and coatings.

Mixing state of biomass burning particles by single particle aerosol mass spectrometer in the urban area of PRD, China

“…Previous studies have also shown that biomass burning significantly contributed to the regional haze, and led to deterioration of air quality (bin Abas et al, 2004;Li and Shao, 2009;Warneke et al, 2009;Li et al, 2010). The light-scattering efficiency of fine particulate nitrate was also reported to be higher than that of sulfate (Appel et al, 1985).…”

“…The chemical composition of biomass burning particles was measured using off-line analysis (Wang et al, 2009b), which required long collection periods in which additional chemical reactions on the filters may have biased the data. To the best of our knowledge, there has heretofore been scant use of single particle mass spectrometry to analyze the mixing state of biomass burning and its impact on particle chemistry in China (Li and Shao, 2009;Li et al, 2010). …”

Internally Mixed Sea Salt, Soot, and Sulfates at Macao, a Coastal City in South China

“…2,19,30 The humid coastal air, therefore, promotes water uptake on the aged aerosol particles. The Na-rich and ammoniated sulfate particles were assumed to deliquesce in the early morning with RH of 80-90%.…”

“…As a result of the atmospheric processing, aerosols show diverse changes in their chemical and physical properties, such as chemical composition, size, morphology, and hygroscopicity. [1][2][3] These changes can affect the role of aerosols in the regional climate through the scattering and absorption of solar radiation (direct radiative forcing) or by acting as cloud condensation nuclei (CCN) (indirect radiative forcing). [4][5][6] In order to accurately account for the effects of aerosols on these processes, their detailed species and corresponding chemical and physical properties must be investigated.…”

“…8 In addition to physical attachment, heterogeneous reactions of sea salt and mineral dust particles in the atmosphere can affect their properties. 2,3 Through laboratory experiments it is becoming increasingly clear that ubiquitous sea salt and alkaline mineral dust can heterogeneously react with acidic gases (e.g., SO 2 , NO 2 , HNO 3 , and organic acids).…”