Abstract
Abstract. A total of 834 individual aerosol particles were collected during October and November 2010 in urban Shanghai, China. Particles were sampled under different weather and air quality conditions. Morphologies, compositions and mixing states of carbonaceous aerosols were investigated by transmission electron microscopy (TEM) coupled with energy-dispersive X-ray (EDX). Structures of some particles were verified using selected-area electron diffraction (SAED). Among the aerosol particles observed, carbonaceous aerosols were mainly categorized into four types: polymeric organic compound (POC), soot, tar ball, and biogenic particle. Based on the detailed TEM-EDX analysis, most of the particles were coated with secondary organic aerosols (SOA), which commonly formed through condensation or heterogeneous reactions of precursor gases on pre-existing particles. Aged particles were associated with days with low wind velocities, showed complex structures, and were bigger in size. The internally mixed particles of sulphates, organics and soot were encountered frequently. Such internally mixed particles may be preferentially formed during a stagnated air mass during serious pollution events, such as on 13 November. Although relative number counts varied with different species, sulphates (38–71%) and soot (11–22%) constituted the most dominant species observed in the samples. However, soil-derived particles (68%) were relatively more frequently observed on the sample collected on 12 November during a dust storm.
Highlights
Carbonaceous aerosols exert great influence on climate by changing the energy transfer through the atmosphere, and potentially affect public health as carriers of toxic chemicals (Jacobson, 2001; Ramana et al, 2010; Utsunomiya et al, 2002; Menon et al, 2002)
energy-dispersive X-ray (EDX) spectra were recorded in transmission electron microscopy (TEM) image show any changes in the beam, whereas the organic coatmode and quantified using ES Vision software that ings and the internally mixed particles containing sulphates uses the thin-foil method to convert X-ray counts of each invariably changed under the electron beam; an analysis of element into atomic or weight percentages
Since Posfai et al (2003) proposed that tar balls were probably correspond to an intermediate stage in the aging of organic particles from biomass burning, we strongly suspected that a fraction of K-containing polymeric organic compound (POC) could be originated from tar balls
Summary
Carbonaceous aerosols exert great influence on climate by changing the energy transfer through the atmosphere, and potentially affect public health as carriers of toxic chemicals (Jacobson, 2001; Ramana et al, 2010; Utsunomiya et al, 2002; Menon et al, 2002). The large usage of coal and biofuel burning, the increasing number of automobiles, rapid urbanization, and flourishing construction activities are all causing the high aerosol loadings (Gao et al, 2009; Ramana et al, 2010; Zhou et al, 2009) These factors make Shanghai air pollution difficult to control (Fu et al, 2008). Carbonaceous aerosols emitted from Shanghai are still not well known, especially by single particle analysis, they may have a significant impact on air quality of Yangtze River Delta and climate changes of east China. Toward this end we have employed the TEM-EDX technique to characterize carbonaceous aerosols in Shanghai. We expected to gain insight into their formation and sources on local, regional, and long-range levels, and to possibly make a contribution to the determination of the impact of these aerosols on regional air pollution in east China
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