Pollution events

A Safety Case is a narrative that literally makes the case that an adequate level of safety has been reached for an installation. It requires looking at all potential hazards which could lead to a loss of the installation, a loss of life, or a major pollution event. A risk analysis is performed on each hazard evaluating the probability of the event occurring and describing the magnitude of the consequences. A discussion is then given of the measure undertaken to lower the probability of occurrence or to mitigate the consequences and a case is made that the risk for the installation meets the ALARP safety criteria. 

The extreme events which have been discussed differ in their characteristic spatial scales of importance. Each event which causes wind-throw occurs on a smaller spatial scale than a pollution event, as recently seen by the very extensive scale of the Chernobyl fallout (Johnston, 1987). At an even greater scale, the projected extent of the nuclear winter will be global (Covey, 1987). Examples of this hierarchy of scales of events are shown in Table 1. 

Episodic pollution events can adequately be addressed by acute toxicity bioassays, however these are not sufficient to investigate the water quality for delayed toxicity effects of chemicals present. Chronic effects of pesticides can include carcinogenicity, teratogenicity, mutagenicity, neurotoxicity, and reproductive effects (endocrine disruption). 

There are a wide range of bioremediation technologies either in use or proposed for use on oil/gasoline-contaminated land [301, 319], and these can be divided into two broad groups. In situ techniques treat the contamination at the site of the pollution event, whereas ex situ techniques remove the contamination from the ground and transfer it to another location for treatment. The use of in situ treatment is often preferable in terms of financial considerations, due to the cost of moving large quantities of soil [20]. Some novel approaches to the problem of hydrocarbon contamination of contaminated aqueous-solid phase environments is the use of (1) gas-liquid foams to enhance in situ bioremediation, and (2) biostimulation, as follows. 

You are responsible for the safe operation of a drinking-water supply system that gets its raw water from a well located close to a river. From tracer experiments you know that the effective mean flow velocity is u =3 m d l and that the distance along the streamline from the point of infiltration to the well is x = 18 m. The dispersivity of the aquifer for this distance of flow is aL = 5 m. In order to be prepared for a possible pollution event in the river you are interested in the following questions ... 

For tropospheric ozone, the residual technique was pioneered by Fishman et al. (1990), who used total O3 column, estimated from TOMS, combined with the co-located stratospheric ozone profiles from SAGE or SBUV in a series of studies to demonstrate the presence of elevated tropospheric ozone for large-scale pollution events (Fishman et al., 1991 1992 1996). 

Figure 6. Biomass burning and pollution event observed above Indonesia from GOME excess tropospheric column amounts of N02, HCHO, 03 and die true colour picture showing clouds and biomass burning smoke...

TWA sampling can be used in situations where analyte concentrations are variable and can be used to measure episodic pollution events. As integrative samplers permit the measurement of concentrations over extended time periods, they can provide a more realistic picture of contaminant levels than can be achieved by the collection of discrete spot samples of water. 

Environment Sensors monitoring air and water quality will be able to provide early warning of pollution events arising at industrial plants, landfill sites, reservoirs, and water distribution systems at remote locations. The environmental nervous system concept likens the rapid access and response capabilities of widely distributed sensor networks to the human nervous system that is, it is able to detect and categorize events as they happen, and organize an appropriate response. 

The model for experimental results, which has been developing, reduces and sorts various information into manageable portions, but it only hints at the way in which these pieces fit together. What must now be sought are patterns that can unite them into descriptions and explanations of the effects of air pollutants. There are many possible patterns, but those that suit the form of our information and embody the ideas of temporal and spatial order are probably the most useful. Thus, the characteristics of receptors, pollutants, events, and environ-... 

Its average SO2 emission rate ( 4,000-5,000 Mg d b is similar to the total industrial sulfur flux from France (Allard et al., 1991) and must result in substantial elevations in tropospheric sulfate in southern Italy (Graf et al., 1998). It has been suggested that these emissions have caused pollution events in mainland Italy, and even that they have been responsible for deterioration of Roman monuments (Camufifo and Enzi, 1995). Etna also pumps an astonishing estimated 700 kg of gold into the atmosphere every year (Table 6). 

Regional pollution events and long-distance transport... 

Ozone also has a significant impact on the global troposphere, and ozone chemistry is a major component of global tropospheric chemistry. Global background ozone concentrations are much lower than urban or regional concentrations during pollution events, but there is evidence that... 

Most other major cities in the USA and in Europe also record events with ozone in excess of 125 ppb, but these occur only a few times per year. Severe air pollution events occur less frequently in these cities, because the meteorological conditions that favor rapid formation of ozone (high sunlight, warm temperatures, and low rates of dispersion) occur less frequently. Significant excess ozone is formed only when temperatures are above 20 °C, and smog events are usually associated with temperatures of 30 °C or higher. In the major cities of northeastern USA and northern Europe, ozone levels exceed 80 ppb on —30-60 days per year. At other times, a combination of cool temperatures and/or clouds prevents ozone formation, regardless of the level of precursor emissions. 

The most severe pollution events occur when a combination of light winds and suppressed vertical mixing prevents the dispersion of pollutants from an urban center. The process of ozone formation typically requires several hours and occurs only at times of bright sunlight and warm temperatures. Eor this reason, peak ozone values typically are found downwind of major cities rather than in the urban center. During severe events with light winds, high ozone concentrations are more likely to occur closer to the city center. 

Figure 1 Peak ozone concentrations in the eastern United States during a severe air pollution event (June 15, 1988) based on surface observations at 350 EPA monitoring sites. The shadings represent values of 30-60 ppb (lightest shading) to 180-210 ppb (darkest shading) with 30 ppb intervals in between. Values reported for Canada and the Atlantic Ocean are inaccurate, since no observations were available for these locations (first printed in Sillman, 1993) (reproduced by permission of Annual Reviews from Annual Reviews of Energy and the Environment, 1993,18, 31-56).

The relative impact of NO, . and VOCs on ozone formation during pollution events represents a major source of uncertainty. The chemistry of ozone formation is highly nonlinear, so that the exact relation between ozone and precursor emissions depends on the photochemical state of the system. Under some conditions, ozone is found to increase with increasing NO , emissions and to remain virtually unaffected by changes in VOCs. Under other conditions, ozone increases rapidly with increased emission of VOCs and decreases with increasing NO. This split into NOj -sensitive and NOjc-saturated (or VOC-sensitive) photochemical regimes is a central feature of ozone chemistry and a major source of uncertainty in formulating pollution control policy. 

Biogenic sources of NO are generally too small to contribute signihcantly to pollution events. Biogenic emissions represent —5% of total NO emissions in the USA (compared to 50% of total VOCs) (Williams et al, 1992). Biogenic NO emissions can be important in intensively farmed regions, where soil emission of NO is enhanced by heavy use of fertilizers. 

Ozone air pollution events generally have lower concentrations of sulfates than the winter fog events, because the dynamics that lead to ozone production usually have much more rapid vertical dilution than the fog events. However, ozone events can lead to a significant enhancement of sulfates, especially at the regional scale. The same photochemical processes that lead to ozone formation also cause rapid photochemical conversion of sulfur dioxide to sulfates. Conversion of sulfur dioxide to sulfates during air pollution events occurs on a timescale of 1-2 days. This allows for significant accumulation of sulfates during regional air pollution events. 

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