1Laboratory of Radiochemistry and Environmental Chemistry, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
2EMPA, Swiss Federal Laboratories for Materials Research and Testing, Electronics/Metrology Laboratory, Ueberlandstrasse 129, 8600 Dübendorf, Switzerland
3Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
4Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
*now at: swissQuant Group AG, Kuttelgasse 7, 8001 Zurich, Switzerland
**now at: Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), UTAPRAD-DIM, Via E. Fermi 45, 00044 Frascati, Italy
Abstract. Soot particles can significantly influence the Earth's climate by absorbing and scattering solar radiation as well as by acting as cloud condensation nuclei. However, despite their environmental (as well as economic and political) importance, the way these properties are affected by atmospheric processing is still a subject of discussion. In this work, soot particles emitted from two different cars, a EURO 2 transporter, a EURO 3 passenger vehicle, and a wood stove were investigated on a single-particle basis. The emitted exhaust, including the particulate and the gas phase, was processed in a smog chamber with artificial solar radiation. Single particle specimens of both unprocessed and aged soot were characterized using x-ray absorption spectroscopy and scanning electron microscopy. Comparison of the spectra from the unprocessed and aged soot particles revealed changes in the carbon functional group content, such as that of carboxylic carbon, which can be ascribed to both the condensation of secondary organic compounds on the soot particles and oxidation of primary soot particles upon photochemical aging. Changes in the morphology and size of the single soot particles were also observed upon aging. Furthermore, we show that the soot particles take up water in humid environments and that their water uptake capacity increases with photochemical aging.