Aerosols and hydrosols
Aerosols and hydrosols represent particulate matter suspended in a carrier medium, e.g. air or water. The size ranges from a few nanometers up to some micrometers.
Aerosols are sometimes the unwanted product of a technical process. Diesel exhaust may serve as a typical example. The upcoming engine generation will release only minor concentrations of diesel soot. Diesel exhaust aftertreatment is currently a hot topic among the diesel car manufacturers. Beside a refined particle trap, also re-injection of a part of engine exhaust into the running engine is part of the reduction means. Here, the oxidation reactivity of the released soot particles is of tremendous importance. Also, availability of on-line measurement tools for direct observation of soot emission is essential.
The Institute of Hydrochemistry IWC (identical with the Chair of Analytical Chemistry) has a long lasting experience with soot aerosol. Within several projects Raman microspectroscopy, operated at different laser wavelengths, is established for the first time to characterize the nanocrystallinity of nanometer-sized soot. Depending on the nanocrystallinity of the primary particles a diesel exhaust particle filter can be operated at lower temperatures. The current measurement technology for instantaneous measurement of rapidly changing soot concentrations, as it is the case in instationary engine test cycles, stems also from the IWC. Laser photoacoustic spectroscopy is in the meantime world-wide in use. Currently, this technology becomes extended by a parallel NOx sensor device. On-board diagnostic for permanent control of soot exhaust aftertreatment is required from 2013 on. One technology is based on conductivity measurement of deposited soot particles. We are currently studying the intrinsic conductivity of selected soot nanoparticulates.
Other topics around nanometer-sized aerosols are chemical reactions occuring at aerosol surfaces. Here especially the formation of nitrated polycyclic aromatic substances (Nitro-PAHs) is in the focus of trace-analytical studies. Modern exhaust aftertreatment technologies make use of the great oxidation potential oh hot NO2, which is anyway produced by a diesel engine. In the course of such technology NO2 has a chance to nitrate soot-adsorbed PAHs. Possible formation products are super-mutagenic Nitro-PAHs.
Hydrosols are the counterpart to aerosols, but dispersed in aqueous phase. In natural water they often consist of biological matter, e.g. viruses. Up to now, no reliable analytical technique exists to evaluate them in clean water, e.g. drinking water. The IWC is developing enrichment techniques, based on cross flow filtration, followed by monolithic receptor columns and immunomagnetic separation steps. By this, viruses from 30.000 L water are concentrated up into a final volume of 500 mL . From there they become analysed by microarray technology
A completely new way to characterize and separate dispersed nanoparticles is photophoresis. Here we apply strong laser beams to create perpendicular force fields due to photon momentum transfer and/or photothermophoresis. Currently, a first prototype is established which kicks particles by photophoretic forces from one particle flow into another one in parallel. This procedure can be applied to dispersed microorganisms or any tiny particulate.