Joachim Eichhorn

Simulation of effects of vegetation on the dispersion of pollutants in street canyons

An extension of the numerical model MISCAM to account for effects of vegetation is presented. Computed wind and turbulence profiles agree reasonably with wind tunn el data. Furthermore, the extended model yields plausible results for flow fields and pollutant distribution s in an idealized street canyon with and without vegetation. While wind speed is reduced within the vegetated street canyon, a slight increase of pollutant concentrations is found. Zusammenfassung

Validation of a Microscale Pollution Dispersal Model

The three-dimensional numerical model MISCAM (Micro Scale Air Pollution Model) has been developed to study wind flow and pollutant dispersal in densely built-up urban areas (Eichhorn, 1989). The model has been successfully applied for planning purposes by a variety of institutions in Germany. MISCAM consists of the non-hydrostatic Eulerian equations of motion and a transport equation for pollutants. Turbulence closure is carried out by means of a k-e-model. To reduce numerical diffusion errors, Smolarkiewicz and Grabowski’s (1989) scheme may be used for the calculation of advective transport. Additionally, sedimentation and dry deposition of pollutants may be taken into account.

Traffic-related immissions and their impact on historic buildings: implications from a pilot study at two German cities

Besides the enormous improvement of air quality in Germany due to the reduction of sulphur dioxide emissions in the last decades, high immissions of nitrogen oxides and fine particulate matter are frequently observed at traffic-rich urban sites. The changed chemical composition of air pollution requires a new investigation of its impact on historic buildings constructed of natural stone. In a pilot study a multi-disciplinary approach was chosen to obtain information on the actual pollution situation of historic buildings and monuments at traffic hotspots in Germany. The study concentrated on the two German cities of Munich and Mainz of different size, traffic volume and stone inventory. Dose–response functions were calculated to demonstrate the change of impact of different pollutants over the last three decades, and for comparison of traffic hotspots and housing areas of both cities. Numeric modelling on a city-scale was used to identify the historic buildings and monuments affected by elevated traffic immissions. Because a relevant part of these pollutants is dominated by short-range transport, the differences of wind speed and deposition rates were calculated using a street-scale 3D flow and dispersion model regarding traffic volume, wind regime and adjacent buildings. Finally, particulate matter was sampled at different positions of two buildings heavily exposed to traffic emissions. Individual particles were investigated by environmental scanning electron microscopy. After classification of the particles into different chemical groups, the fraction of traffic-induced particulate matter was quantified. Summarizing the results, it must be stated that soiling by traffic-related particulate matter, deposition of nitrates deriving from exhaust emission and other diffusely emitted components bear a severe damage potential for natural building stone at least locally at traffic-rich urban sites.

Salt deposition and soiling of stone facades by traffic-induced immissions

Despite enormous enhancements in air quality, many cities still have serious problems to comply with the legal limits of air pollution. Concentrations of nitrogen oxides and fine particulate matter remain high, originating in relevant proportions from urban traffic. The impact of traffic-induced immissions on our built heritage is the focus of this study. The proportion of historic buildings exposed to elevated traffic emissions was estimated in five German cities of different sizes and different traffic loads. Less than 100 up to more than 1000 historic buildings per city are exposed to increased traffic emissions. For five buildings at heavy-trafficked roads, the near-field air flow and the deposition rate of air pollutants were modelled. Passive samplers were exposed at these buildings to determine the composition and amount of particulate matter, the concentrations of NO2 and HNO3 in the air, as well as the soiling and the recession rate of stone samples. The results clearly demonstrate the deposition of large amounts of particulate matter and the corresponding soiling of stone samples as consequences of road traffic. Despite high concentrations of NO2, the deposition of nitrates on stone surfaces seems to play a limited role. In addition, the deposition of sulphate and at some exposure sites chloride deposition was observed.