In Germany, the number of small wood-burning combustion plants was around 11 million in 2020. The PM2.5 immissions caused by the operation of these combustion plants are already about as high as those from traffic exhaust gases. Thus, particulate matter immissions occur not only on busy roads but also in residential areas. Since there are few official measuring stations for PM2.5 in residential areas and suburbs, this study determined PM2.5 concentrations from November 2020 to June 2021 at three stations (urban, suburban, and residential) in the Karlsruhe area. Simultaneous measurements of PM2.5 at the three locations have been implemented to determine short-term (peaks), medium-term, and long-term particulate matter levels and to assign them to sources by observation, considering wind direction. Illustratively, PM2.5 immission levels in January and May 2021 were compared in this paper. The comparison of the particulate matter immissions measured in the urban and residential area in January revealed that PM2.5 concentration peaks of up to 60 µg/m³ occurred for short periods in the residential area, especially on Fridays and in the evenings, which could be assigned to wood stove operation. In the urban and suburban areas, the number of the immission peaks was lower by 70–80%, and the peak concentrations were also lower by an average of 13–18%. However, the high short-term peaks have no significant impact when calculating the PM2.5 annual average according to the current limit value regulation (39. BImSchV).

Wall-flow filters are a standard component in exhaust gas aftertreatment and have become indispensable in vehicles. Ash and soot particles generated during engine combustion are deposited in diesel or gasoline particulate filters. During regeneration, the soot particles are oxidized. The remaining ash particles can form different deposition patterns: a homogenous layer or plug-end filling. It has not yet been clarified whether the plug-end filling is first formed by rearrangements of agglomerates before and during the regeneration of the reactive particles. In this study, experiments are carried out with a single channel of a wall-flow filter. For the investigations, a layer of inert and reactive particles is formed. The rearrangement of agglomerates is achieved by flowing through the model filter channel and observed with a high-speed camera. The particulate structures detach at the channel inlet, are transported along the channel and deposited at the plug. The velocity of the detached agglomerates depends on their size, shape, track and the gas velocity in the channel. If the agglomerate is near the walls of the model filter channel, the gas velocity deviates from the gas velocity in the core flow. The higher the gas velocity, the higher the agglomerate velocity achieved and the larger the detached agglomerates.

Particulate filters are used as a standard component in the exhaust gas aftertreatment of vehicles. The reactive (soot) and inert (ash) particles generated during engine operation are deposited in wall-flow filter. The resulting particle layer increases the differential pressure of the filter, which is why it is regenerated regularly. During regeneration of the filter, the reactive particles oxidize, and the inert particles remain in the filter. The oxidation of the soot particles results in a layer break-up, and the resuspension of particle structures can occur. The layer break-up over the entire length of an inlet channel and the resuspension of particle structures have not yet been observed, which is why the fundamental processes in a particulate filter have not yet been fully clarified. In these investigations, the regeneration of a single wall-flow filter channel is observed in situ with high temporal and spatial resolution. For this purpose, the filter is loaded with soot particles and regenerated subsequently. The regeneration of the filter is analyzed in relation to the process parameters of temperature, layer thickness, and flow velocity. Before the visual layer break-up, the pressure drop decreases and declines to a constant value before resuspension of particle structures are detected. As the temperature is increased, the regeneration time is reduced. With a thicker particle layer, the particle structures formed during layer break-up become larger, the location of resuspension shifts to the posterior channel region, and the number of resuspensions increases. A higher flow velocity causes more particle structures to be resuspended and transported to the channel end.

Ash and soot particles are generated during engine combustion and are deposited in particulate filters. In order to understand the basic processes that occur in a particulate filter during the filtration process the particles have to be generated quickly and replicably. In this study, fundamental investigations are conducted on the generation of ash particles independently of an engine to produce a defined aerosol. The formation of ash particles from engine oils with differences in sulfate ash content (SAC; 0.7%, 2.6%, 4.5%) as well as the variation of process parameters (oil temperature, nozzle volume flow) are investigated. The ash particles are produced by nebulizing engine oil and a subsequent thermal conversion in a furnace. The SAC of the oil does influence the ash particles that are generated. With the increase of the SAC, the ash mass flow and the number weighted median diameter increase. Raising the nozzle volume flow as well as the oil temperature leads to an increase in total number concentration and mass flow of the ash particles. The number median diameter of the oil mist and ash particles decrease with the increase of oil temperature and nozzle volume flow. For the fast loading of a particulate filter, the SAC of the oil should be 4.5%. The oil temperature and nozzle volume flow should be set at 30 °C and 6 L·min⁻¹. In conclusion, the ash generation method can be used for the rapid loading of a particulate filter.