Concentrations in cities

Figure 7. Maximum 8-hour 1y CO concentrations in cities, 1980-1984. SOURCE Adapted from Ref 8.

Nickel in air is attached to small particles. Over a 6-year period (1977-1982) in the United States, average nickel concentrations in cities and in the country ranged from 7 to 12 nanograms per cubic meter (ng/m 1 ng/m is equivalent to 1 billionth of a gram in a cubic meter of air). 

Computational compliance modelling has given a preliminary indication that there is scope to further reduce lead concentrations in City A by orthophosphate dosing, but operational feasibility would first need to be confirmed. Computational compliance modelling indicates that the current plumbosolvency control treatment measures in City B are close to optimum by pH elevation alone. 

Fig. 4-2. Typical central city diurnal variation in carbon monoxide concentration, in a city in the United States. Spring (------), summer (------), fall (..), winter (----).

Fig. 21-7, Relative concentration in seconds per meter (s m ) exceeded in a 10-km city on 10% of all mornings (solid lines) and 10% of all afternoons (dashed lines). Source After Holzworth (2),...

Silver ions can be found in some of the city water piped into homes. The average concentration of silver ions in city water is 0.028 ppm. 

Over 65% of the global population Is living In urban areas where the concentration levels of particles are considered to be unacceptably high. In contrast less than 20% of the people are living In cities considered to have acceptable levels of particles. 

Figure 6 shows a cumulative probability plot of both the maximum dally and hourly NO2 averages In cities for the 1980-84 time period. The plotted values can be directly compared to the WHO guideline values of 150/tg/m3 for the maximum 24-hour level and 400/tg/m3 for the maximum 1-hour level. In both cases, about 25% of the cities worldwide exceed the guideline values. Based on these proportions of cites with NO2 concentrations above the short-term guideline values. It Is estimated that approximately 15-20 percent of urban residents In North America and Europe are at Increased risk to short-term high NO2 exposures. 

A very tentative conclusion from the relatively small sample of cities studied shows that people living In as many as half the cities In the world may be exposed to CO concentrations In excess of the WHO short-term guideline. 

Carey AE, Douglas P, Tai H, et al. 1979a. Pesticide residue concentrations in soils of five United States cities, 1971-Urban Soils Monitoring Program. Pestic Monit J 13 17-22. 

Potentiometric instrnments are nsed most often when analyzing harmful contaminants in the air at production sites or in cities. Electrodes, whose potential is, as a rule, a linear fnnction of the logarithm of concentration of the substance to be determined (by Nemst s law), are the sensing elements in snch instruments. Most potentiometric sensors are highly selective. 

Abulfaraj WH, Ahmed M, Mousli KM, et al. 1990. Measurement of ambient air lead concentrations in the city of Jeddah, Saudi Arabia. Environ Inter 16 85-88. 

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