However, two technical limitations have prevented the use of this method in the past. First, the lateral resolution of conventional instruments is not sufficient to determine aerosol particles with diameters below approximately 200 nm. The study of morphological details, which are important for the assignment of particles into groups with defined optical properties, requires the use of high-resolution instruments.

Second, conventional instruments are often equipped with energy-dispersive detectors, which do not allow detection of the light elements carbon, nitrogen, and oxygen. Therefore, carbon-rich particles, the most important absorbing component of many atmospheric aerosols, could not be studied appropriately in the past. In addition, scanning electron microscopy does not provide information on the phase composition. However, this information is needed in order to assign physical properties (e.g., refractive index) to individual particles.

We have overcome these problems by using high-resolution scanning electron microscopy (field emission gun) and transmission electron microscopy for particle characterization. Both instruments are equipped with modern energy-dispersive X-ray microanalysis systems, enabling the detection of light elements like carbon and nitrogen. Only this combination of techniques enables an almost complete characterization (size, morphology, chemical composition, phase composition) of the climatological most important size range (100 nm – 3 µm) of atmospheric aerosols.