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Introduction & BackgroundDAPPLE is a 4-year EPSRC funded project whose aim is to enhance understanding of pollutant dispersion processes in realistic urban environments and thereby make possible improvements in predictive ability that will enable better planning and management of urban air quality. The work also intends to quantify the determinants of human exposure to air pollution as sources and people move together through the urban environment. The greater aim is to assist in the the evaluation and development of appropriate decision support tools, to permit the development of sustainable, safer, and more pleasant cities worldwide.

DAPPLE brings together a multidisciplinary research group, from six universities (Bristol, Cambridge, Imperial, Leeds, Reading & Surrey), that is capable of undertaking field, wind tunnel and computational simulations so as 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. 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. This poster introduces the background of the DAPPLE project and details the measurements made during the first field campaign in central London, NW1, 28 April – 24 May 2003. For the most current information please refer to the web site at http://www.dapple.org.uk.

Dispersion of Air Pollution and its Dispersion of Air Pollution and its Penetration into the Local EnvironmentPenetration into the Local Environment

Presented by Surbjit Kaur, Imperial College; Presented by Surbjit Kaur, Imperial College; Corresponding Author: s.arnold@imperial.ac.uk; Project Leader: a.robins@surrey.ac.ukCorresponding Author: s.arnold@imperial.ac.uk; Project Leader: a.robins@surrey.ac.uk

The novel aspects of DAPPLE, distinguishing it from other previous urban air pollution experiments, are:

multidisciplinary nature of the project – field components cover met., pollution, traffic flow, personal exposure and tracer releases;

focus on an urban intersection (Fig. 1), rather than a 2-D street canyon, as very few cities are composed of long, uninterrupted street canyons;

investigation of the determinants of exposure at intersections, where there is the close proximity of pollution sources, the traffic, and the receptors, the people.

Fig. 1 Idealised urban intersection.

Field Site & MeasurementsThe measurements were centred at Westminster City Council (WCC) on the intersection of Marylebone Road and

Gloucester Place, with a surrounding study area approximately 250 m in radius (Fig. 2). Marylebone Rd is a busy dual carriageway (A501) and forms the northern boundary of the London Congestion-Charging Zone. Gloucester Place is 3 lanes, one-way north (Baker Street is southbound one block to the East). The roads intersect perpendicularly and Marylebone Rd is at a 20 ˚ angle north of due east, approximately WSW-ENE. Existing long term measurements show this to be one of the most polluted regions of London with background NO2 levels almost continuously, and up to 4 times, above the European air quality 2005 limit value of 21 ppb.

The DAPPLE fixed location instrumentation included - 7 ultrasonic anemometers (logging at 5 & 20 Hz), 2 automatic weather stations (AWS, 30 s averages) and 10 CO Streetboxes. These instruments were mounted on street furniture (Fig. 6) along Marylebone Rd between WCC and Marylebone Rd AURN Supersite, courtesy of Transport for London (TfL). Additional measurements included SCOOT traffic data, measurements within the traffic using the Leeds Instrumented Vehicle (Fig. 5a), an inert tracer release experiment conducted from York Street (Fig. 4b), personal exposure measurements made by people passing through the area (Fig. 3a), and indoor-outdoor measurements of VOC’s and particulate matter.

MeteorologyInvestigation will concentrate on how the horizontal transport compares with the vertical mixing in urban environments (Fig. 6) and how the flow within the streets relates to the more commonly measured synoptic data (data from Met Office). Initial results suggest that channelling effects dominate the horizontal transport in the street, despite the proximity to the crossroads, for example:• Site 4 (Fig. 2) is constrained in the E-W direction and flows are dominated by the winds channelled along the relatively narrow Gloucester Place (16 m). The direction of flow at street level varying by 180 ˚ based on whether the synoptic winds are N or S; • For W synoptic winds Site 1 is relatively unconstrained in all directions (Fig. 2) and flow in the street is decomposed into its constituent components, switching intermittently between Marylebone Rd and Gloucester Place.

Background Pollution and TrafficThe results from the CO Streetbox monitors (Fig. 5b) capture many of the characteristics of the site (Fig. 2). Over night the CO levels tend to zero as would be expected when the main source of pollution, the traffic, is at its minimum. During the working week two CO peaks can be identified associated with the morning and evening rush hours (absent at weekends). Changing synoptic conditions, which drive the in-street flows and are the source of any imported pollution, show: • HP systems, with light E winds, generate high pollution episodes; • Prevailing LP systems with SW winds, result in more subtle differences in the distribution of pollution depending on the obliqueness of the synoptic flow to Marylebone Rd i.e. S winds support a flow across the top of the canyon from S to N, and a counter flow at ground level sweeping the pollution to the S pavement; along the road winds support more uniform mixing throughout the canyon.

PMCH concentration for integrated 3 minute samples

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Sites 1 – vertical pair of Streetboxes at 7 & 4 m.

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Ref. AWS KEY: Streetbox (CO) at 4 m (unless otherwise stated).

Sonics at 8m Central reservation of Marylebone Rd

Vertical Pair of Sonics, Site 4 = 4 & 8 m, Site 5 = 8 & 12 m.

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Supersite outside Westminster University, co-located Streebox at 2m for calibration

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Fig. 2 Map of field site, intersection of Marylebone Road and Gloucester Place,

London, NW1.

Personal Exposure AssessmentDuring the DAPPLE exposure assessment groups of four volunteers (Fig. 3a) carried PTraks (real time ultra fines), Langans (10 s CO) and ultraflow pumps (for time-averaged PM2.5) through the study area (Fig. 7) along Marylebone Road and the back streets (Fig. 2). Four modes of transport (walking, cycling, bus & car/taxi) were investigated at 3 different times during the day (morning, lunch & afternoon).Work in collaboration with the Health and Safety Laboratory has combined video imagery (Fig. 3b) with the real time exposure measurements and this allows the causes of the peak particle concentrations e.g. the passing of a bus, to be identified.

Tracer Release Experiment, 5 pm, 15 May 2003The tracer experiment concentrated on near-source dispersion with 10 sample sites located downwind, within approx. two blocks of the release site (Fig. 2). The release was undertaken from a vehicle parked in York Street using SF6 and the perfluorocarbon tracer PMCH. Both tracers were released for 15 minutes each, offset by 1.5 minutes. At the sampling stations, 10 consecutive air bag samples of 3 minute averages were taken (Fig. 4a). All but one of the sampling stations (WCC roof) was at ground level. Throughout the release SSW winds prevailed as a cold front approached (Fig. 4b). Initial results from confirm the success of the release with the perfluorocarbons present in the air samples collected.

The success of the first DAPPLE measurement campaign has meant that the consortium is now in a position to open the second experiment, dates set as 19 April – 28 May 2004, to other interested parties. To take advantage of the permissions gained to work in central London please contact Alan Robins (a.robins@surrey.ac.uk) in the first instance to discuss possible collaborations for either the testing of equipment in an urban environment and/or full participation in the next phase of the DAPPLE field measurements.

Fig. 6 Ultrasonic anemometer on Marylebone Rd lamp post.

Fig. 7 Field site intersection of Marylebone Rd and Gloucester Place.

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Fig. 5(b) Streetbox CO values for the N (yellow key) and S (blue key) of Marylebone Road during mainly SSW winds.

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Fig. 5(a) ITS Leeds instrumented vehicle.

Fig. 3(a) Exposure volunteers.

Fig. 4(a) Preliminary results of PMCH conc. for 5 of the 10 sampling sites during the tracer release experiment.

Fig. 4(b) Synoptic chart for 15 May.

Fig. 3(b) H&SL video & data.