Wilhelm Kuttler

On the reduction of urban particle concentration by vegetation - a review

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.

Study of the thermal structure of a town in a narrow valley

Abstract This study examines the influence of urban and topoclimatic factors on the temperature field of Stolberg, Germany, a densely built up town in a valley, on the basis of stationary and mobile measurements during cloudless and nearly calm weather conditions. Qualitative and quantitative statements are made about the extent of influence by invariable parameters (percentage of sealed area, height) and by variable conditions (wind velocity, time, temperature amplitude) on thermal conditions in the investigated area. An observed influence of cold air on the temperature field near the ground required further study of wind field influences due to topographic conditions and of an analysis of intensity and frequency of valley inversions. Regarding clear and calm weather conditions, results show a significant relationship between thermal conditions and the percentage of sealed area, as well as topographical height. As a result of roughness of the built up area, the nocturnal urban excess temperature is not reduced by cold air drainage until the second half of the night. The high production of cold air causes the nocturnal component of a mountain and valley wind regime:, which explains the accelerated cold air transport from above the urban canopy layer as well as the frequency of valley inversions. While ground level inversions exist in the rural area of the valley, the urban heat island effect causes an inversion at a higher level above the developed valley area.

Nocturnal Secondary Ozone Concentration Maxima Analysed by Sodar Observations and Surface Measurements

Abstract The occurrence of nocturnal secondary ozone maxima was investigated by ground-level meteorological and air quality measurements in an urban park in Essen, Germany, during 29 individual summer measurement campaigns between May 1995 and September 1997. In addition, during an intensive measurement campaign in May 1997, SODAR measurements of wind and turbulence were made. The spatial and temporal distribution of nocturnal ozone maxima within the measurement network of the Environmental Protection Office of North Rhine–Westphalia was also analysed. Two case studies of nocturnal secondary ozone maxima are discussed in more detail. They represent two different types of this phenomenon, associated with a nocturnal low-level jet (LLJ) and the passage of a front, respectively. In both cases, the nocturnal increase in ozone concentration was accompanied by a significant increase in the standard deviation of the vertical wind speed σw across the lower stable boundary layer, indicating enhanced vertical mixing. During the LLJ case, ozone maxima were observed at 33% of the stations of the Environmental Protection Office network at approximately the same time. In the case of the front, the time of the ozone concentration rise could be allocated to the time of the passage of the front, moving from northwest to southeast across the study area. For the first time, the measurements presented here document turbulent mixing induced by shear forces in the whole layer between the core of the LLJ and the ground surface during secondary nocturnal ozone maxima.

The dependence of the urban heat island intensity on latitude : A statistical approach

The question about a possible dependence of the Urban Heat Island (UHI) on latitude and its causes has not been solved satisfactorily up to now. This paper tries to give an answer to the problem by extracting the UHI of cities on a global scale from the available international scientific literature and treating them with various statistical methods. In addition parameters like the city population, use of primary energy, topographic features, height above sea level and the energy balance of the earths surface are included into the statistical calculations in order to substantiate a latitudinal variation of the UHI. Three main results could be derived from the statistical examinations, namely: 1. The UHI shows a trend to increase from low to high latitudes 2. The part of the observed variance of the UHI explained by its latitudinal variation, however, remains relatively small with about 6 %. 3. A statistically significant dependence of the UHI on latitude is based mainly on the latitudinal variation of anthropogenic heat production and radiation balance.

The significance of country breezes for urban planning

Abstract The increase of horizontal air exchange in agglomeration areas, especially during weather conditions with low wind velocities, is crucial in urban planning. In this connection the mesoscale circulation induced by an urban heat island, i.e., a country breeze (‘Flurwind’), is of great importance for the improvement of the ventilation in built-up areas. An insight into the characteristic flow patterns of country breezes and their implications for urban planning purposes necessitates continuous measurements. This paper presents an analysis of recorded wind data at five stations over a period of 16 months. The area under investigation was Bochum, a town located in the heart of the densely populated Ruhr industrial region in the Federal Republic of Germany. The results show that country breezes occurred during 10% of the total measuring time in the city of Bochum. The records, including the spatial and temporal structure of country breezes, confirm that this kind of wind regime must be regarded as an essential element in urban planning.

The Urban Climate - Basic and Applied Aspects

Towns and cities are the most densely populated areas on Earth and will continue to be the artificial landscapes most widely used by the greater part of the Earth’s population in the future. In 2030 more than 60% of humans will live in cities. Changes in urban conditions have often caused deterioration in environmental quality and may result in damage to the health of city-dwellers. The differences between the climate of a city and the climate of its surroundings are referred to as the “urban climate”. The most important features of urban climate include higher air and surface temperatures, changes in radiation balances, lower humidity, and restricted atmospheric exchange that causes accumulations of pollutants from a variety of sources. Although these changes mainly affect local or regional conditions, persistent substances released into the atmosphere may also affect larger areas or even the global climate.

Biogenic and anthropogenic isoprene in the near-surface urban atmosphere — A case study in Essen, Germany

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.

Variability of particle number concentration and particle size dynamics in an urban street canyon under different meteorological conditions

During a six-month study period, aerosol number size distributions, mean meteorological conditions and turbulent exchange were measured within an urban street canyon in Essen, Germany. The findings were compared to simultaneous measurements conducted at suburban sites within the study area. The effects of turbulent exchange and different canyon flow situations on aerosol number concentration variability within the street canyon were studied. In comparison to a suburban background site, the busy urban street canyon aerosol number concentration was significantly elevated in the size range below 70 nm throughout the daytime hours. During the morning rush hour, total number concentrations were a factor of 2.2 higher. On average, the total number concentration at the street canyon site roughly doubled the suburban background concentrations (by a factor of 1.9). The intensity of turbulent mixing within the street canyon was sensitive to the prevailing flow regime. The highest turbulent mixing during cross-canyon flow from directions downwind of the measurement spot was accompanied by the lowest number concentration of all flow regimes observed within the canyon. This behaviour was consistent for the different aerosol size classes considered in this study. The effects of meteorology and traffic intensity on total aerosol number concentrations were parameterised using a multiple linear regression analysis and indicated that turbulent mixing within the canyon, traffic intensity and NOx concentrations were the most significant parameters. The model is characterised by an average relative uncertainty of 29%. During situations with a total number concentration>7500 cm(-3), a relative uncertainty of the modelled data of ±25% emerges but displays a larger deviation for low particle concentrations.

Dewfall measurements on Lanzarote, Canary Islands

At Lanzarote, Canary Islands, condensation is considered to play a significant role in the water budget of fields mulched with porous volcanic products (Picon). Here, 68 nights of gravimetric condensation measurements with mulched and bare surfaces, along with meteorological measurements were carried out. Results presented here indicate two major findings of interest with respect to general assumption: Firstly, nocturnal condensation on the mulch surface is lower than on a dry bare (loam) soil surface. A slightly higher nocturnal cooling of the mulched surface, and resulting higher dewfall in the strict sense, is overcompensated by the stronger hygroscopic properties of the soil. Secondly, dewfall, though otherwise consistent in magnitude and meteorological dependency with empirical and theoretical knowledge in literature, can still be observed at high wind speeds (u 10 m s -1 at 10 m a.g.l.) in northern to north-eastern trade winds that carry moist air from the sea. Dewfall to the mulched surface was observed in 39 of the measurement nights with a mean nocturnal sum of 0.07 mm.

Klimawandel im urbanen Bereich, Teil 1, Wirkungen

Ziel dieses Beitrags, der in zwei Teilen erfolgt, ist es, die Wirkungen des globalen Klimawandels auf einen Ballungsraum (Ruhrgebiet) zu untersuchen und Gegenmasnahmen auf lokaler Ebene zu diskutieren. Im ersten Teil wird auf die Entstehung des naturlichen und anthropogenen Treibhauseffektes eingegangen und deren jeweilige Beitrage an der globalen Uberwarmung herausgestellt. Exemplarisch wird auf die jungere Klimaentwicklung in der Metropolregion Ruhr eingegangen. Zu den durch verschiedene numerische und statistische Modelle projizierten Klimaveranderungen zahlen auch die Zunahme thermischer Belastungen fur die Stadtbevolkerung sowie die Verstarkung sommerlicher konvektiver Niederschlage mit entsprechenden Abflussspitzen. Unter den Luftverunreinigungen wird es in erster Linie das bodennahe Spurengas Ozon sein, dass bei ansteigenden Temperaturen eindeutig hohere Konzentrationen erwarten lasst, wohingegen die atmospharischen Feinstaubkonzentrationen (≤ PM10) bislang keine enge Bindung an die Temperaturentwicklung erkennen lassen. Im zweiten Teil der Publikation wird anhand verschiedener anwendungsorientierter Beispiele gezeigt, wie dem globalen Klimawandel auf lokaler Ebene wirksam begegnet werden kann. Hierzu zahlen objektbezogene wie auch flachenabhangige Masnahmen, deren Ziel es ist, sowohl die urbane Uberwarmung als auch die Emission an CO2 wirksam zu reduzieren.The objective of this article, which is being published in two parts, is to investigate the effects of global climate change on a conurbation (the Ruhr area) and to discuss local counter-measures.Part 1 deals with the origins of the natural and anthropogenic greenhouse effects, presents the contributions of the two effects to global warming and discusses recent examples of climate development from the Ruhr metropolis. The climate changes projected by various numeric and statistical models include an increase in thermal stress for city-dwellers and a rise in convective precipitation with corresponding run-off peaks in summer. As regard air pollutants (e.g. O3, PM10), it will mainly be the concentration of the near-surface trace gas ozone which will be clearly increased with rising temperatures. In contrast, a close correlation between atmospheric fine dust concentrations (≤ PM10) and temperature changes has not yet been established.Part 2 of the publication indicates how global climate change can be effectively combated at the local level using a number of application-oriented examples. These include measures affecting both individual properties and whole areas with a view to reducing urban overheating and CO2 emissions.ZusammenfassungZiel dieses Beitrags, der in zwei Teilen erfolgt, ist es, die Wirkungen des globalen Klimawandels auf einen Ballungsraum (Ruhrgebiet) zu untersuchen und Gegenmaβnahmen auf lokaler Ebene zu diskutieren.Im ersten Teil wird auf die Entstehung des natürlichen und anthropogenen Treibhauseffektes eingegangen und deren jeweilige Beiträge an der globalen Überwärmung herausgestellt. Exemplarisch wird auf die jüngere Klimaentwicklung in der Metropolregion Ruhr eingegangen. Zu den durch verschiedene numerische und statistische Modelle projizierten Klimaveränderungen zählen auch die Zunahme thermischer Belastungen für die Stadtbevölkerung sowie die Verstärkung sommerlicher konvektiver Niederschläge mit entsprechenden Abflussspitzen. Unter den Luftverunreinigungen wird es in erster Linie das bodennahe Spurengas Ozon sein, dass bei ansteigenden Temperaturen eindeutig höhere Konzentrationen erwarten lässt, wohingegen die atmosphärischen Feinstaubkonzentrationen (≤ PM10) bislang keine enge Bindung an die Temperaturentwicklung erkennen lassen.Im zweiten Teil der Publikation wird anhand verschiedener anwendungsorientierter Beispiele gezeigt, wie dem globalen Klimawandel auf lokaler Ebene wirksam begegnet werden kann. Hierzu zählen objektbezogene wie auch flächenabhängige Maβnahmen, deren Ziel es ist, sowohl die urbane Überwärmung als auch die Emission an CO2 wirksam zu reduzieren.