In order to assess the filtration performance of plants with respect to atmospheric dust, deposition on vegetation has been investigated by a number of different methods (field studies, numerical and physical modelling) over the past few years. The intention of this review is to assess the extent to which a reduction in particle concentration (especially PM 10) can be accomplished by existing vegetation or targeted planting on the basis of international publications. The range of this assessment however is limited to the quantitative filtration potential of urban vegetation. Deposition velocity was taken as a measure of filtration performance as a particle deposited on a plant is in effect taken from the atmosphere. As regarding published deposition velocities, there are differences of an order of magnitude between measured values and the results of model calculations. The average published value (∼1 cm s −1) corresponds to a reduction in pollutant concentration (PM 10) of about 1 % in urban areas. In addition, analyses carried out for a busy arterial road show that very large vegetation areas (in excess of 10,000 m 2) would be needed to compensate for local emissions of particles (PM 10) by vehicles at a deposition velocity of 1 cm s −1. However, current in-situ measurements indicate deposition velocities considerably higher than 1 cm s −1 and, for PM 1 , velocities above 10 cm s −1. If these results were confirmed by further measurements, local planting campaigns covering small areas could also be beneficial for a reduction of particle concentrations. Zusammenfassung Um die Filterwirksamkeit von Pflanzen gegenüber Partikeln zu bestimmen, wurde in den vergangenen Jahren mit einer Vielzahl von Methoden (Feldstudien, Modellierung, Windkanal) die Deposition auf Vegetationsoberflächen untersucht. Die Intention dieses Reviews ist es auf der Basis von internationaler Literatur zu bewerten, inwieweit eine Reduktion der Immissionskonzentration von Partikeln (insbesondere von PM 10) durch vorhandene Vegetation bzw. durch gezielte Pflanzmaßnahmen möglich ist. Diese Einschätzung beschränkt sich jedoch vom Umfang her auf das quantitative Filterungspotential städtischer Vegetation. Als Maß für die Filterleistung wurde die Depositionsgeschwindigkeit herangezogen, da mit der Deposition auf den Pflanzen auch eine Entnahme aus der Luft einhergeht. Die veröffentlichten Depositionsgeschwindigkeiten zeigen Unterschiede von bis zu einer Größenordnung zwischen den gemessenen Werten und den Ergebnissen aus Modellrechnungen. Berechnet man mit einem Mittelwert der veröffentlichten Werte (∼1 cm s −1) das Reduktionspotential für den städtischen Raum, erhält man eine Verringerung der Immissionskonzentration (PM 10) von ca. 1 %. Analysen für eine belastete Ausfallstraße zeigen außerdem, dass bei einer Depositionsgeschwindigkeit von 1 cm s −1 beispielsweise eine Kompensation der lokalen Kfz-Emissionen von PM 10 erst bei sehr großen Vegetationsflächen (> 10 000 m 2) möglich ist. Aktuelle in-situ Messungen weisen jedoch auf Depositionsgeschwin...

Cities represent thermal load areas compared with their surrounding environments. Due to climate change, summer heat events will increase. Therefore, mitigation and adaptation are needed. In this study, meteorological measurements in various local climate zones were performed to demonstrate the influence of evaporation surfaces and other factors on thermal comfort, as determined by the physiologically equivalent temperature (PET). Furthermore, a quantification of the thermal effects of several adaptation measures and varying meteorological parameters was made using model simulations (ENVI-met) in an inner-city neighborhood (Oberhausen, Germany). The results show that the most effective adaptation measure was increased wind speed (maximal 15 K PET reduction). Moreover, vegetation areas show greater PET reductions by the combination of shading and evapotranspiration than water surfaces. The creation of park areas with sufficient water supply and tall, isolated, shade-providing trees that allow for adequate ventilation can be recommended for planning.

Abstract:Urban/rural humidity differences were analysed by means of a climate station pair in Krefeld (51°20 N, 6°33 E), Germany, during the period from 11/2001 to 10/2002, on the basis of hourly averages of water vapour pressure. Focus was put upon on the examination of frequency, timing and duration of the Urban Moisture Excess (UME) ( e u−r > 0 hPa). It was found that the urban site was more humid (0 hPa < e u−r ≤ 0.5 hPa; weak UME) in 31.4% of the cases investigated and was only rarely significantly more humid ( e u−r > 0.5 hPa; intense UME) in 4.6%. Weak and intense UME occur during every month of the year with different frequencies per month. A diurnal course of UME was found for summer but not for winter. Weak and intense UME events show frequency maxima in the second half of the night. Most of them are characterized by durations of 1 hour, in few cases several hours duration were observed for weak (up to 14 h) and intense UME (up to 12 h).The main reason for formation of UME events might be that the surface dew point at the rural station was reached more often, earlier and lasted longer in comparison to the urban environment.

No abstract

Isoprene is emitted in large quantities by vegetation, exhaled by human beings and released in small quantities by road traffic. As a result of its high reactivity, isoprene is an important ozone precursor in the troposphere and can play a key role in atmospheric chemistry. Measurements of isoprene in urban areas in Central Europe are scarce. Thus, in Essen, Germany, the isoprene concentration was measured at various sites during different seasons using two compact online GC-PID systems. Isoprene concentrations were compared with those of benzene and toluene, which represent typical anthropogenic VOCs. In the summer, the diurnal variation in isoprene concentration was dependent on the biogenic emissions in the city. It was found that its maximum concentration occurred during the day, in contrast to the benzene and toluene concentrations. During the measurement period in the summer of 2012, the average hourly isoprene concentrations reached 0.13 to 0.17 ppb between 10 and 20 LST. At high air temperatures, the isoprene concentration exceeded the benzene and toluene concentrations at many of the sites. Isoprene became more important than toluene with regard to ozone formation in the city area during the afternoon hours of summer days with high air temperatures. This finding was demonstrated by the contributions to OH reactivity and ozone-forming potential. It contradicts the results of other studies, which were based on daily or seasonal average values. With an isoprene/benzene ratio of 0.02, the contribution of anthropogenic isoprene decreased substantially to a very low level during the last 20 years in Central Europe due to a strong reduction in road traffic emissions. In the vicinity of many people, isoprene concentrations of up to 0.54 ppb and isoprene/benzene ratios of up to 1.34 were found in the atmosphere due to isoprene exhaled by humans.