Remarkable dynamics of nanoparticles in the urban atmosphere

Nanoparticles emitted from road traffic are the largest source of respiratory exposure for the general public living in urban areas. It has been suggested that the adverse health effects of airborne particles may scale with the airborne particle number, which if correct, focuses attention on the nanoparticle (less than 100 nm) size range which dominates the number count in urban areas. Urban measurements of particle size distributions have tended to show a broadly similar pattern dominated by a mode centred on 20–30 nm diameter particles emitted by diesel engine exhaust. In this paper we report the results of measurements of particle number concentration and size distribution made in a major London park as well as on the BT Tower, 160 m high. These measurements taken during the REPARTEE project (Regents Park and BT Tower experiment) show a remarkable shift in particle size distributions with major losses of the smallest particle class as particles are advected away from the traffic source. In the Park, the traffic related mode at 20–30 nm diameter is much reduced with a new mode at <10 nm. Size distribution measurements also revealed higher number concentrations of sub-50 nm particles at the BT Tower during days affected by higher turbulence as determined by Doppler Lidar measurements and indicate a loss of nanoparticles from air aged during less turbulent conditions. These results suggest that nanoparticles are lost by evaporation, rather than coagulation processes. The results have major implications for understanding the impacts of traffic-generated particulate matter on human health

What is an Urban Atmosphere?

Atmosphere is one of the key ideas in contemporary aesthetics. The concept proves to be exceptionally useful whenever particular spaces, including interiors or urban spaces, are discussed regarding their unique features. The goal of the paper is to reconsider how an urban atmosphere may be understood. In order to do that, we will shed light on the ontological nature of atmospheres, by revisiting the concept as it recently was presented by some influential proponents of the aesthetics of atmospheres. Contrary to the widespread view, we argue that an atmosphere is not an entity itself. It is not a “quasi-thing” or “half-thing,” as usually stated, but rather a relational feature of a given site that exists only when it is experienced by someone. At the same time, our discussion of the metaphysics of atmospheres will provide us with a better understanding of the idea of urban atmosphere as characteristic of a particular site. Moreover, the ontology we will sketch allows us to consider the idea of an atmosphere of a whole city

What is an Urban Atmosphere?

Atmosphere is one of the key ideas in contemporary aesthetics. The concept proves to be exceptionally useful whenever particular spaces, including interiors or urban spaces, are discussed regarding their unique features. The goal of the paper is to reconsider how an urban atmosphere may be understood. In order to do that, we will shed light on the ontological nature of atmospheres, by revisiting the concept as it recently was presented by some influential proponents of the aesthetics of atmospheres. Contrary to the widespread view, we argue that an atmosphere is not an entity itself. It is not a “quasi-thing” or “half-thing,” as usually stated, but rather a relational feature of a given site that exists only when it is experienced by someone. At the same time, our discussion of the metaphysics of atmospheres will provide us with a better understanding of the idea of urban atmosphere as characteristic of a particular site. Moreover, the ontology we will sketch allows us to consider the idea of an atmosphere of a whole city

Fogwater chemistry in an urban atmosphere

Analyses of fogwater collected by inertial impaction in the Los Angeles basin and the San Joaquin Valley indicated unusually high concentrations of major and minor ions. The dominant ions measured were NO_3^−, SO_4^(2−), NH_4^+, and H^+. Nitrate exceeded sulfate on an equivalent basis by a factor of 2.5 in the central and coastal regions of the Los Angeles basin but was approximately equal in the eastern Los Angeles basin and the San Joaquin Valley. Maximum observed values for NH_4^+, NO_3^−, and SO_4^(2−) were 10.0, 12.0, and 5.0, meq 1^(−1), while the lowest p;H observed was 2.2. Iron and lead concentrations of over 0.1 mM and 0.01 mM, respectively, were observed. High concentrations of chemical components in fog appeared to correlate well with the occurrence of smog events. Concentrations in fogwater were also affected by the physical processes of condensation and evaporation. Light, dissipating fogs routinely showed the highest concentrations

Fractionation of particulate and vapor phase fluoride in urban atmosphere

The distribution of fluoride between particulate and gaseous phases in the urban atmosphere of an industrialized city has been investigated. A new method was developed for collection of gaseous and particulate phase of fluoride. A comparison was made between the results obtained from the proposed method with those obtained from the traditional method using mixed cellulose ester (MCE) and showed an excellent agreement. The proposed method was applied for fractionation of fluoride in urban atmosphere. The seasonal variation in concentrations of gaseous and particulate fluoride in the atmosphere of the city was also investigated and showed higher concentrations of fluoride fractions in autumn and winter seasons

Assessing contributions of agricultural and nonagricultural emissions to atmospheric ammonia in a Chinese megacity

Ammonia (NH3) is the predominant alkaline gas in the atmosphere contributing to formation of fine particles—a leading environmental cause of increased morbidity and mortality worldwide. Prior findings suggest that NH3 in the urban atmosphere derives from a complex mixture of agricultural (mainly livestock production and fertilizer application) and nonagricultural (e.g., urban waste, fossil fuel-related emissions) sources; however, a citywide holistic assessment is hitherto lacking. Here we show that NH3 from nonagricultural sources rivals agricultural NH3 source contributions in the Shanghai urban atmosphere. We base our conclusion on four independent approaches: (i) a full-year operation of a passive NH3 monitoring network at 14 locations covering urban, suburban, and rural landscapes; (ii) model-measurement comparison of hourly NH3 concentrations at a pair of urban and rural supersites; (iii) source-specific NH3 measurements from emission sources; and (iv) localized isotopic signatures of NH3 sources integrated in a Bayesian isotope mixing model to make isotope-based source apportionment estimates of ambient NH3. Results indicate that nonagricultural sources and agricultural sources are both important contributors to NH3 in the urban atmosphere. These findings highlight opportunities to limit NH3 emissions from nonagricultural sources to help curb PM2.5 pollution in urban China

Cool marble building envelopes. The effect of aging on energy performance and aesthetics

Marble envelopes represent a relatively common architectural solution used in variety of historic, modern and contemporary building facades. White marble envelopes have been shown to reduce solar heat gains, while improving indoor thermal comfort and energy efficiency in summer time. While marble is useful in this context, the urban atmosphere accelerates the degradation of marble elements. This leads to changes in optical characteristics, hence the aesthetics, and affects the energy efficiency benefits offered by white marble facades. These issues are investigated in order to predict the impact of degradation on energy performance and to the aesthetic value, such as change of color and luminosity. In this study, surface degradation of white marble is analyzed by means of accelerated weathering in the laboratory while examining changes to the optical characteristics of the materials. A dynamic simulation is carried out to assess the energy performance of a building as a case study

Urban Atmospheric Chemistry::A Very Special Case for Study

Abstract Studies of the chemistry of the urban atmosphere provide special challenges which arise from the high density of emissions, strong concentration gradients and relatively high pollutant concentrations. In contrast to the regional and global atmosphere, local dispersion processes play a much larger role in determining atmospheric concentrations and also have a substantial effect on chemical transformations. On the other hand, residence times in the urban atmosphere are relatively short, hence limiting the range of chemical reaction processes which are significant. Some key species such as the hydroxyl radical have different predominant source processes in the urban and the regional atmosphere. A case is made that the differences are so large that urban atmospheric chemistry needs to be given special treatment and cannot simply be considered as subtlely different from regional and global atmosphere studies

Ambient halocarbon mixing ratios in 45 Chinese cities

During this study 158 whole air samples were collected in 45 Chinese cities in January and February 2001. The spatial distribution of different classes of halocarbons in the Chinese urban atmosphere, including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), Halon-1211, and other chlorinated compounds is presented and discussed. Most of these compounds were enhanced compared to background levels. However, the mean enhancement of CFCs was relatively small, with CFC-12 and CFC-11 increases of 6% (range 1-31%) and 10% (range 2-89%), respectively, with respect to the global background. On the contrary, strongly enhanced levels of CFC replacement compounds and halogenated compounds used as solvents were measured. The average Halon-1211 concentration exceeded the background of 4.3 pptv by 75% and was higher than 10 pptv in several cities. Methyl chloride mixing ratios were also strongly elevated (78% higher than background levels), which is likely related to the widespread use of coal and biofuel in China. © 2006 Elsevier Ltd. All rights reserved