Urban area

In urban areas, sampling strategies for storm water runoff from industries and municipalities are of specific importance. The United States Federal Storm Water Regulations of 1990 specify protocols for such storm water nmoff sampling. These regulations define two separate samples that must be collected when a storm occurs. A first-flush sample is to be collected during the first 30 min of the storm event. A flow-weighted composite sample must be collected for the entire storm event or at least the first 3 h of the event [8]. 

The first-flush sample and the flow-weighted composite sample must be analyzed for the pollutants listed in Table 1.3. In general, the sample volume required for laboratory analysis depends on the particular pollutants being monitored and varies for each application. As a general rule, a 3 L sample volume for both first-flush and flow-weighted composite sample usually is sufficient for the majority of applications [8]. 

Storm Water Analysis Requirements according to the United States Federal Storm Water Regulations 

Source From Friling, L., Pollut. Eng., 25, 36,1993. With permission. 

Both manual and automatic methods can be used to collect samples for the required analysis [8]. For manual sampling, the samples can be taken at fixed time intervals in individual bottles. After collection, a specific volume must be poured out of each bottle to form a flow-weighted composite. The exact volume must be calculated using the flow data taken when each bottle was filled. The advantage of manual sample collection is that, regardless of runoff amount, a fairly constant volume of sample is collected. This is because the flow-weighted composite is formed after the event and does not depend on calculations for runoff volume. 

Substantial quantities of lead emitted in vehicle exhaust gases are deposited directly onto the road surface. Shaheen [11] has carried out one of the most comprehensive studies of this particular source of lead, based on the Washington DC MetropoHtan Area. The average deposition rate for lead was 7.9 X 10 g per axle-km. However, an important finding of this study was that the accumulation rate of materials deposited on road surfaces prior to washoff is not linearly related to time. The accumulation levels off after several days, due to removal of the deposited material by the passage of vehicles. Thus the ratio of lead accumulated on the road surface after 3 days to that accumulated after 1 day was found to be only 1.2 1. 

The highway is undoubtedly the most important source of lead in urban runoff [12, 13]. Rain washes the lead, most of which is associated with particulate matter, off the road, transporting it via an efficient drainage system directly to local water courses or in the case of a combined sewerage system to a treatment plant. It has been found that a simple exponential model can be used to describe the removal of surface contaminants [12] 

Hedley and Lockley [14] have examined the runoff from an 800 m section of 

7-lane urban motorway. The average daily runoff of lead was 190 g day S the level being much higher in winter than in summer. A small percentage of this runoff, 1 4%, was due to lead contamination of the de-icing salt used extensively during the winter. 

A more detailed study of sub-catchments in a Virginia watershed [7] yielded lead discharge rates of 0.92 g ha day for a low density residential area and 2.3 g ha day for drainage from a commercial area. Similar results have been obtained in England for a small catchment of mature housing, where the discharge was 0.11 g ha day [13]. Traffic flow in the area was reported as 9500 vehicles day  

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Tropospheric residence time only shorter lifetime appUes to urban areas where NO quickly destroys O. ... 

Emissions of CO in the United States peaked in the late 1960s, but have decreased consistendy since that time as transportation sector emissions significandy decreased. Between 1968 and 1983, CO emissions from new passenger cars were reduced by 96% (see Exhaust CONTUOL, automotive). This has been partially offset by an increase in the number of vehicle-miles traveled annually. Even so, there has been a steady decline in the CO concentrations across the United States and the decline is expected to continue until the late 1990s without the implementation of any additional emissions-reduction measures. In 1989, there were still 41 U.S. urban areas that exceeded the CO NAAQS on one or mote days per year, but the number of exceedances declined by about 80% from 1980 to 1989. Over the same time period, nationwide CO emissions decreased 23%, and ambient concentrations declined by 25% (4). 

Airborne manganese concentrations in the United States range from 0.02 to 0.57 in urban areas and 0.0017-0.047 in nonurban areas. 

Phthalates in Air. Atmospheric levels of phthalates in general are very low. They vary, for DEHP, from nondetectable to 132 ng/m (50). The latter value, measured in 1977, is the concentration found in an urban area adsorbed on airborne particulate matter and hence the biological avaUabUity is uncertain. More recent measurements (52) in both industrial and remote areas of Sweden showed DEHP concentrations varying from 0.3 to 77 ng/m with a median value of 2 ng/m. ... 

Although stream standards are the most reaUstic in light of the use of the assimilative capacity of the receiving water, they are difficult to administer and control in an expanding industrial and urban area. The equitable allocation of poUutional loads for many industrial and municipal complexes also poses pohtical and economic difficulties. A stream standard based on minimum dissolved oxygen at low stream flow intuitively implies a minimum degree of treatment. One variation of stream standards is the specification of a maximum concentration of a poUutant (ie, the BOD) in the stream after mixing at a specified low flow condition. 

Models can be used to study human exposure to air pollutants and to identify cost-effective control strategies. In many instances, the primary limitation on the accuracy of model results is not the model formulation, but the accuracy of the available input data (93). Another limitation is the inabiUty of models to account for the alterations in the spatial distribution of emissions that occurs when controls are appHed. The more detailed models are currendy able to describe the dynamics of unreactive pollutants in urban areas. 

Because of the expanded scale and need to describe additional physical and chemical processes, the development of acid deposition and regional oxidant models has lagged behind that of urban-scale photochemical models. An additional step up in scale and complexity, the development of analytical models of pollutant dynamics in the stratosphere is also behind that of ground-level oxidant models, in part because of the central role of heterogeneous chemistry in the stratospheric ozone depletion problem. In general, atmospheric Hquid-phase chemistry and especially heterogeneous chemistry are less well understood than gas-phase reactions such as those that dorninate the formation of ozone in urban areas. Development of three-dimensional models that treat both the dynamics and chemistry of the stratosphere in detail is an ongoing research problem. 

Location and space available (urban areas, sensitive equipment around, limited space. . . )... 

The Britter and McQiiaid model was developed by performing a dimensional analysis and correlating existing data on dense cloud dispersion. The model is best suited for instantaneous or continuous ground-level area or volume source releases of dense gases. Atmospheric stability was found to have little effect on the results and is not a part of the model. Most of the data came from dispersion tests in remote, rural areas, on mostly flat terrain. Thus, the results would not be apphcable to urban areas or highly mountainous areas. 

Another test looked at nitrate concentrations in 229 urban areas in the UK between 1969 and 1973 and at deaths from stomach cancer in the same areas at the same time. The hypothesis suggested that there should be a positive relationship between them. The results showed a negative one. 

Soil resistivity measurements can be affected by uncoated metal objects in the soil. Values that are too low are occasionally obtained in built-up urban areas and in streets. Measurements parallel to a well-coated pipeline or to plastic-coated cables give no noticeable differences. With measurements in towns it is recommended, if... 

Whereas cathodic protection—apart from a few exceptions—can be relatively easily applied outside built-up areas, in urban areas difficulties arise due to the numerous metallic installations below ground. Interference with nearby installations has to be considered, on account of the relatively high protection currents (see Section 9.2). 

In Fig. 15-9 two potentiostatically controlled protection rectifiers and an additional diode are included to drain peak currents. At pipeline crossings with an external rail network (e.g., in regions outside the urban area), the forced stray current drainage should be installed as close as possible to the rails that display negative potentials for the longest operation time. The currents absorbed from the positive rails continue to flow also in the region outside the rail crossings. Here the use of potentiostatically controlled rectifiers is recommended these should be connected not only to the rails but also to impressed current anodes. 

Combined Stray Current Protective Measures in Urban Areas... 

There are two different types of air pollution problems in urban areas. One is the release of primary pollutants (those released directly from sources). The other is the formation of secondary pollutants (those that are formed through chemical reactions of the primary pollutants). 

What are the two types of air pollution problems found in urban areas ... 

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