As part of the DAPPLE programme two large scale urban tracer experiments using multiple simultaneous releases of cyclic perfluoroalkanes from fixed location point sources was performed. The receptor concentrations along with relevant meteorological parameters measured are compared with a three screening dispersion models in order to best predict the decay of pollution sources with respect to distance. It is shown here that the simple dispersion models tested here can provide a reasonable upper bound estimate of the maximum concentrations measured with an empirical model derived from field observations and wind tunnel studies providing the best estimate. An indoor receptor was also used to assess indoor concentrations and their pertinence to commonly used evacuation procedures.

The DAPPLE (Dispersion of Air Pollutants and their Penetration into the Local Environment) project seeks to characterise near-field urban atmospheric dispersion using a multidisciplinary approach. In this paper we report on the first tracer dispersion experiment carried out in May 2003. Results of concurrent meteorological measurements are presented. Variations of receptor tracer concentration with time are presented. Meteorological observations suggest that in-street channelling and flow-switching at intersections take place. A comparison between roof top and surface measurements suggest that rapid vertical mixing occurs, and a comparison between a simple dispersion model and maximum concentrations observed are presented. Copyright (C) 2010 Royal Meteorological Society

Street-level mean flow and turbulence govern the dispersion of gases away from their sources in urban areas. A suitable reference measurement in the driving flow above the urban canopy is needed to both understand and model complex street-level flow for pollutant dispersion or emergency response purposes. In vegetation canopies, a reference at mean canopy height is often used, but it is unclear whether this is suitable for urban canopies. This paper presents an evaluation of the quality of reference measurements at both roof-top (height = H) and at height z = 9H = 190 m, and their ability to explain mean and turbulent variations of street-level flow. Fast response wind data were measured at street canyon and reference sites during the six-week long DAPPLE project field campaign in spring 2004, in central London, UK, and an averaging time of 10 min was used to distinguish recirculation-type mean flow patterns from turbulence. Flow distortion at each reference site was assessed by considering turbulence intensity and streamline deflection. Then each reference was used as the dependent variable in the model of Dobre et al. (2005) which decomposes street-level flow into channelling and recirculating components. The high reference explained more of the variability of the mean flow. Coupling of turbulent kinetic energy was also stronger between street-level and the high reference flow rather than the roof-top. This coupling was weaker when overnight flow was stratified, and turbulence was suppressed at the high reference site. However, such events were rare (<1% of data) over the six-week long period. The potential usefulness of a centralised, high reference site in London was thus demonstrated with application to emergency response and air quality modelling.

The paper describes a field study focused on the dispersion of a traffic-related pollutant within an area close to a busy intersection between two street canyons in Central London. Simultaneous measurements of airflow, traffic flow and carbon monoxide concentrations ([CO]) are used to explore the causes of spatial variability in [CO] over a full range of background wind directions. Depending on the roof-top wind direction, evidence of both flow channelling and recirculation regimes were identified from data collected within the main canyon and the intersection. However, at the intersection, the merging of channelled flows from the canyons increased the flow complexity and turbulence intensity. These features, coupled with the close proximity of nearby queuing traffic in several directions, led to the highest overall time-average measured [CO] occurring at the intersection. Within the main street canyon, the data supported the presence of a helical flow regime for oblique roof-top flows, leading to increased [CO] on the canyon leeward side. Predominant wind directions led to some locations having significantly higher diurnal average [CO] due to being mostly on the canyon leeward side during the study period. For all locations, small changes in the background wind direction could cause large changes in the in-street mean wind angle and local turbulence intensity, implying that dispersion mechanisms would be highly sensitive to small changes in above roof flows. During peak traffic flow periods, concentrations within parallel side streets were approximately four times lower than within the main canyon and intersection which has implications for controlling personal exposure. Overall, the results illustrate that pollutant concentrations can be highly spatially variable over even short distances within complex urban geometries, and that synoptic wind patterns, traffic queue location and building topologies all play a role in determining where pollutant hot spots occur.

Empirical models for particulate matter emissions from paved road surfaces have been criticised for their lack of realism and accuracy. To support the development of a less empirical model, a study was conducted in a busy street at the DAPPLE site in Central London to understand the processes and to identify important parameters that influence emission from paved roads. Ordinary road gritting salt was applied to the road and the particulate matter entering the air at near-road surface level was monitored using optical particle counters. The grit acted as a tracer. The grit moved rapidly along the road in the direction of traffic flow. Build-up of material at the kerb indicated material being thrown across the road by the traffic. Coarser particles were resuspended faster than the finer ones. A clear decay profile was seen in the case of particles larger than 2μm; particles smaller than 2μm did not show any decay pattern during the experiment duration. Grinding of material appears to control the reservoir of fine particles on the road surface. The amount of material resuspended by traffic is about 30% less than those removed along the road and a factor of 6 higher than the amount removed across the road. Resuspension accounts for 40% of the total material removed from a road segment and 70% of the material removed together along and across the road. On average a single vehicle pass removes 0.08% of material present on a road segment at that instant. The calculation scheme is obtained from a short-duration study and therefore further studies of long duration involving varying road geometry and different traffic and meteorological condition need to be carried out before applying parameter estimates presented in this paper.

A field campaign aimed at observing the near-surface flow field across and downwind of a mountain range on the Falkland Islands, South Atlantic, is described. The objective was to understand and eventually predict orographically generated turbulence. The instrumentation was based primarily on an array of automatic weather stations (AWSs), which recorded 30 s mean surface pressure, wind speed and direction (at 2 m), temperature and relative humidity for approximately one year. These measurements were supported by twice-daily radiosonde releases. The densest part of the AWS array was located to the south of the Wickham mountain range, across Mount Pleasant Airfield (MPA). In northerly flow the array provides a detailed study of the flow downwind of the mountain range. The dataset contains several episodes in which the flow downwind of the mountains is accelerated relative to the upwind flow. During some of these episodes short-lived (typically similar to1 hour) periods of unsteady flow separation are observed and these are associated with the formation of rotors aloft. Such events present a significant hazard to aviation at MPA. Examination of radiosonde profiles suggests that the presence of a strong temperature inversion at a height similar to the mountain height is a necessary condition for both downwind acceleration and the formation of rotors. The data are used to show that the downwind fractional speed-up is proportional to the non-dimensional mountain height (based on upstream near-surface winds and a depth-averaged Brunt-Vaisala frequency diagnosed from radiosonde data). Similarly, a relationship is established between a quantity that describes the spatial variability of the flow downwind of the mountains and the upstream wind and depth-averaged Brunt-Vaisala frequency. The dependence of the flow behaviour on the Froude number (defined in the usual way for two-layer shallow-water flow) and ratio of mountain height to inversion height is presented in terms of a flow regime diagram.

Observations were made using a roof-top automatic weather station and four ultrasonic anemometers deployed in the proximity of an intersection in London, UK, during the 4-week DAPPLE project field campaign in spring 2003. At the intersection, the measurements show that the wind direction can switch between the different streets, suggesting that intersections are potent mechanisms for dispersion. Despite the complexity of the building geometry in the vicinity of the intersection, measurements in the adjoining streets indicate that the main large-scale features are along-street channelling and an across-street recirculating vortex, similar to those observed in idealised two-dimensional street canyons. Analysis over a relatively broad range of roof-top wind directions demonstrates that flow within the streets is the vector sum of a channelling and a recirculation vortex. Furthermore, channelling depends linearly on the along-street component of the roof-top reference wind, whilst the cross-street recirculation vortex depends linearly on the component of the roof-top reference wind perpendicular to the street. The results demonstrate that these simple ideas are robust enough to occur in streets of non-ideal geometry and are established a short distance from an intersection.

An increasing number of studies indicate that short-term peak exposures, such as those seen in the transport microenvironment, pose particular health threats. Short-term exposure can only be sufficiently characterised using portable, fast-response monitoring instrumentation with detailed summaries of individual activity. In this paper, we present an exposure visualisation system that addresses this issue—it allows the simultaneous presentation of mobile video imagery synchronised with measured real-time ultrafine particle count exposure of an individual. The combined data can be examined in detail for the contribution of the surrounding environment and the individual's activities to their peak and overall exposure. The exposure visualisation system is demonstrated and evaluated around the DAPPLE study site in Central London using different modes of transport (walking, cycling, bus, car and taxi). The video images, synchronised with the exposure profile, highlight the extent to which ultrafine particle exposure is associated with traffic density and proximity to pollutant source. The extremely rapid decline in concentration with increasing distance away from the pollutant source, such as from the main street to the backstreets, is clearly evident. The visualisation technique allows these data to be presented to both technical audiences and laypersons thus making it an effective environmental risk communication tool. Some exposure peaks however are not obviously associated with any event recorded on video—in these cases it will be necessary to use advanced dispersion modelling techniques to investigate meteorological conditions and other variables influencing in-street conditions to identify their possible causes.

The Dispersion of Air Pollution and its Penetration into the Local Environment (DAPPLE) project brings together a multidisciplinary research group that is undertaking field measurements, wind tunnel modelling and computer simulations in order to provide better understanding of the physical processes affecting street and neighbourhood-scale flow of air, traffic and people, and their corresponding interactions with the dispersion of pollutants at street canyon intersections. The street canyon intersection is of interest as it provides the basic case study to demonstrate most of the factors that will apply in a wide range of urban situations. The aims of this paper are to introduce the background of the DAPPLE project, the study design and methodology for data collection, some preliminary results from the first field campaign in central London (28 April–24 May 2003) and the future for this work. Updated information and contact details are available on the web site at http://www.dapple.org.uk.

view Abstract Citations (24) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Measurement of the diameter of Pluto by speckle interferometry. Arnold, S. J. ; Boksenberg, A. ; Sargent, W. L. W. Abstract For the diameter of Pluto the values of 3000 + or - 400 km, assuming no limb darkening, and 3600 + or - 400 km, assuming limb darkening following a cosine law are obtained. The presence of a degree of limb darkening is possibly indicated by earlier work. The data also show evidence of surface structure, and possibly a strong surface mottling, strong central enhancement in brightness (as would be produced by a semispecular surface), or a combination of both. Values for the average geometric albedo are 0.36 + or - 0.14 (no limb darkening) and 0.25 + or - 0.08 (limb darkening included), consistent with a surface having a large covering of methane frost. From a determination of Pluto's mass using recent data, mean densities of 0.8 (+0.6, -0.3) g/cu cm (no limb darkening) and 0.5 (+0.3, -0.2) g/cu cm (limb darkening included) are obtained. Such low densities suggest that Pluto consists mainly of frozen volatiles. Publication: The Astrophysical Journal Pub Date: December 1979 DOI: 10.1086/183130 Bibcode: 1979ApJ...234L.159A Keywords: Astrometry; Dimensional Measurement; Holographic Interferometry; Pluto (Planet); Speckle Patterns; Albedo; Data Reduction; Diameters; Limb Darkening; Planetary Mass; Planetary Surfaces; PLUTO; DIAMETER; INTERFEROMETRY; SPECKLE TECHNIQUES; SURFACE; ALBEDO; METHANE; FROST; MASS; DENSITY; LIMBS; OBSERVATIONS; DATA REDUCTION; EQUIPMENT; SPECTRUM; PROCEDURE; ANALYSIS; SATELLITES; IMAGE PHOTON COUNTING SYSTEM; Lunar and Planetary Exploration; Pluto; Albedo:Pluto; Density:Pluto; Diameter:Pluto; Pluto:Speckle Interferometry full text sources ADS |

Chemiluminescence attributable to the Swan, Phillips, and Ballik–Ramsay bands of C2 was observed when halomethanes of the form CH2−nX2+n (X = Cl, Br, I) were introduced into a stream of hydrogen atoms. The relative population of the ν′ = 0 levels of the A3Πg, b1Πu and A′ 3∑g− states are 10:400:1000 with the total rate of formation into all three states being approximately equal. The principal step for the formation of C2* is believed to be[Formula: see text]

teristics. Many answers have been suggested and the result is a comparative literature that spans three decades (Angus 1938; Clark 1950; Underhill 1960; Naegele 1961; Horne 1961; Lipset 1963, 1964, 1965; Johnstone 1969). Although this literature has considered many characteristics, it appears that few answers have been supported by empirical evidence. Naegele (1961: 27), for example, has argued that Canadians show &dquo;less willingness to risk capital&dquo; but he has not examined per capita stockholdings or venture capital investment. Horne (1961: 235) has said that Canadians are more adverse to buying on credit but he has not compared credit purchasing statistics. Lipset has recognized this lack of data but he too has primarily depended upon &dquo;impressionistic evidence&dquo; (Lipset 1963: 521) to support his thesis. &dquo;To demon-