Urban canyon

CFD-based models use high-resolution grids to develop a detailed representation of the wind field and are typically used to investigate wind fields within urban (obstacle-rich) environments. The models incorporate detailed representations of each obstacle in the environment and provide the only possible approach to the computation of flows deep within urban canyons (a capability not offered by mesoscale meteorological models). A recent field study of dispersion in New York City provided... 

The structure is ideal for integrated systems where the offset between GPS and GLONASS time may only be known approximately initially, but is known to be virtually constant. This offset would then be estimated as a state variable with some initial uncertainty but with very small Q (fc) driving changes. The same would be true for LORAN/GPS time offsets and the concept could be extended to ASPs for individual stations as well. The ASPs would be represented by very slowly varying states to be estimated. If GPS pseudo-ranges became unavailable such as in an urban canyon, mountain valley, or under heavy foHage cover, the LORAN would now be well calibrated. 

AH calculations based on reference eUipsoid WGS-84 were made on author s simulating program. The interval of the latitude of the observer between 0° and 90° was divided into 9 zones, each 10° wide. In the observer s receiver masking elevation angle Hmin was assumed to be 0° (horizon), 5° fthe most frequently used value of Ihum), 10°, 15° 20° and 25°. The angle 25° is representative for the positioning in restricted area where the visibihty of satelhtes can be limited. This problem is very important in road transport (urban canyon) and in maritime transport. 

An example of matching scale and objective is the determination of CO exposure of pedestrians on sidewalks in urban street canyons. The location of a station to meet this objective would be an elevation of —3 m on a street with heavy vehicular traffic and large numbers of pedestrians. 

More recently, the uptake of water by tropospheric particles in relatively remote locations near the Grand Canyon and in a polluted urban area near Los Angeles was studied by Saxena et al. (1995) using a TDMA similar to the studies of McMurry and co-workers. Figure 9.58 shows the measured total water content of these particles in Claremont, California, east of Los Angeles, as a function of the water calculated to be associated with inorganics. As already discussed, a vari-... 

In most urban regions in Germany traffic emissions are considered the major local PM source. In street canyons PM concentrations caused by traffic emissions may become equal to or higher than the urban background concentrations, hence leading... 

Switzerland Motorway, free flow, 15% heavy duty Urban street canyon 3a (1.6b/9c) 15a (8b/81°) 48a (28b/160c) 27a (lb/262c) [65]... 

Vakeva M, Hameri K, Kulmala M, Lahdes R, Ruuskanen J, Laitinen T (1999) Street level versus rooftop concentrations of submicron aerosol particles and gaseous pollutants in an urban street canyon. Atmos Environ 33 1385-1397... 

Kumar P, Fennell P, Langley D, Britter R (2008) Pseudo-simultaneous measurements for the vertical variation of coarse, fine and ultra fine particles in an urban street canyon. Atmos Environ 42 4304 -319... 

Fig. 16.7 (a) Schematic view of typical element of urban canopy - street canyon (b) Wind flow and pollution dispersion for the part of Copenhagen area... 

Figure 2.7 Low obstacles aligned in rows with angled cross wind (e.g. main and side streets in urban areas). Note that if II/d < 10 a street canyon vortex forms, the wind is deflected along the main street and typically increases with x (complicated by effects of gap between adjacent obstacles e.g. side streets).

Oke [472, 473] differentiated the flows within urban street canyons based on the street width to building height ratio (B/H). The flow was classified as skimming flow (0 < B/H < 1.2), wake interference flow (1.25 < B/H < 5.0), or isolated roughness... 

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