Mapping Carbon in Individual Particles From a Continental Aerosol
Abstract
Knowing the distribution of carbon in distinct aerosol particle types is important for assessing the atmospheric effects of both organic and elemental carbon. We collected aerosol samples at a rural background site in Hungary in all four seasons and under various meteorological conditions. Typically, at this site sulfates and organic species are equally important constituents, and in the summer about half of the organic carbon is water-soluble. The combination of transmission electron microscope imaging with energy-dispersive X-ray spectrometry, electron energy-loss spectroscopy, and energy-filtered elemental mapping allowed the identification of carbon in individual particles at high spatial resolution. All major individual particle types contained carbon. (1) Sulfate particles were invariably coated by an organic film. The coating was 2 to 3 times thicker during pollution episodes than under clean conditions. (2) Soot occurred both externally and internally mixed with sulfates. (3) "Tar balls" contained mostly carbon, they were amorphous, had spherical morphologies and were not aggregated with other species. (4) "Summer sulfates" completely filled the holes of the collecting substrate. This behavior distinguished them from the sulfate particles under (1). Based on variations in the relative concentrations of main particle types under clean and polluted conditions, tar balls seemed to originate from anthropogenic sources, probably wood combustion. The organic coatings on the sulfates could also form from combustion emissions, particularly in the winter samples; however, the different character of the summer and winter sulfates likely indicates that natural organic materials condensed onto sulfates and contributed to the material that formed the coatings on "summer sulfates." Presumably at least some of the water-soluble fraction of the organic carbon resided in the coatings on ammonium sulfate particles.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.A71F..04S
- Keywords:
-
- 0305 Aerosols and particles (0345;
- 4801);
- 0315 Biosphere/atmosphere interactions