Air urban

Lead(II) sulphide is oxidised to lead(II) sulphate this reaction has been used in the restoration of old pictures where the white lead pigment has become blackened by conversion to lead sulphide due to hydrogen sulphide in urban air ... 

T. Y. Chang and S. Rudy, Urban Air QuaHty Impact of Methanol-Pueled Compared to GasoHne-Pueled Vehicles, ia W. Kohl, ed.. Methanol as an yiltemative Fuel Choice yin yissessment,] ohxi Hopkias Poreign PoHcy Institute, Washiagton, D.C., 1990, pp. 97—120. 

Human-made sources cover a wide spectrum of chemical and physical activities and are the major contributors to urban air pollution. Air pollutants in the United States pour out from over 10 million vehicles, the refuse of over 250 million people, the generation of billions of kilowatts of electricity, and the production of innumerable products demanded by eveiyday living. Hundreds of millions of tons of air pollutants are generated annu ly in the United States alone. The five main classes of pollutants are particulates, sulfur dioxide, nitrogen oxides, volatile organic compounds, and carbon monoxide. Total emissions in the United States are summarized by source categoiy for the year 1993 in Table 25-10. 

When a liquid or solid substance is emitted to the air as particulate matter, its properties and effects may be changed. As a substance is broken up into smaller and smaller particles, more of its surface area is exposed to the air. Under these circumstances, the substance, whatever its chemical composition, tends to combine physically or chemically with other particles or gases in the atmosphere. The resulting combinations are frequently unpredictable. Very small aerosol particles (from 0.001 to 0.1 Im) can act as condensation nuclei to facilitate the condensation of water vapor, thus promoting the formation of fog and ground mist. Particles less than 2 or 3 [Lm in size (about half by weight of the particles suspended in urban air) can penetrate the mucous membrane and attract and convey harmful chemicals such as sulfur dioxide. In order to address the special concerns related to the effects of very fine, iuhalable particulates, EPA replaced its ambient air standards for total suspended particulates (TSP) with standards for particlute matter less than 10 [Lm in size (PM, ). 

Brysson and co-workers (7) conducted a study in St. Louis, Missouri, on the effects of urban air pollution on the tensile strength of cotton duck material. Samples were exposed at seven locations for up to 1 year. Figure 9-3 shows the relationship between tensile strength and pollutant exposure. For two levels of ambient air exposure, the materials exhibited less than one-half their initial tensile strength when exposed to air pollution for 1 year. 

When the regional wind allows the outflow to take place in primarily one direction and the rising warm urban air moves off with this regional flow, the circulation is termed the urban plume (Fig. 17-22). Under this circumstance, the inflow to the urban center near the surface may also be asymmetric, although it is more likely to be symmetric than the outflow at higher altitudes. 

Schere, K. L., and Demerjian, K. L., A photochemical box model for urban air quality simulation, in "Proceedings of the Fourth Joint Conference on Sensing of Environmental Pollutants." American Chemical Society, Washington, DC, 1978, pp. 427-433. 

Benarie, M. M., "Urban Air Pollution Modeling." MIT Press, Cambridge, MA, 1980. 

The most widespread and persistent urban pollution problem is ozone. The causes of this and the lesser problem of CO and PMjq pollution in our urban areas are largely due to the diversity and number of urban air pollution sources. One component of urban smog, hydrocarbons, comes from automobile emissions, petroleum refineries, chemical plants, dry cleaners, gasoline stations, house painting, and printing shops. Another key component, nitrogen oxides, comes from the combustion of fuel for transportation, utilities, and industries. 

In the United States, in particular, recent legislation has mandated sweeping improvements to urban air quality by limiting mobile source emissions and by promoting cleaner fuels. The new laws require commercial and government fleets to purchase a substantial number of vehicles powered by an alternative fuel, such as natural gas, propane, electricity, methanol or ethanol. However, natural gas is usually preferred because of its lower cost and lower emissions compared with the other available alternative gas or liquid fuels. Even when compared with electricity, it has been shown that the full fuel cycle emissions, including those from production, conversion, and transportation of the fuel, are lower for an NGV [2]. Natural gas vehicles offer other advantages as well. Where natural gas is abundantly available as a domestic resource, increased use... 

Although the original Clean Air Act of 1977 brought about significant improvements in air quality, the urban air pollution problems of ozone (known as smog), carbon monoxide (CO), and particulate matter (PM,o) persist. Currently, over 100 million Americans live in cities which are out of attaimnent with the public health standards for ozone. The most widespread and persistent urban... 

One example of normal-phase liquid chromatography coupled to gas chromatography is the determination of alkylated, oxygenated and nitrated polycyclic aromatic compounds (PACs) in urban air particulate extracts (97). Since such extracts are very complex, LC-GC is the best possible separation technique. A quartz microfibre filter retains the particulate material and supercritical fluid extraction (SPE) with CO2 and a toluene modifier extracts the organic components from the dust particles. The final extract is then dissolved in -hexane and analysed by NPLC. The transfer at 100 p.1 min of different fractions to the GC system by an on-column interface enabled many PACs to be detected by an ion-trap detector. A flame ionization detector (PID) and a 350 p.1 loop interface was used to quantify the identified compounds. The experimental conditions employed are shown in Table 13.2. 

Figure 13.16 LC separation of urban air particulate exrtact (a), along with the GC/FID cliro-matogram (b) of an oxy-PAC fraction (transfeired via a loop-type interface). Reprinted from Environmental Science and Technology, 29, A. C. Lewis et al., On-line coupled LC-GC-ITD/MS for the identification of alkylated, oxygenated and nirtated polycyclic aromatic compounds in urban air particulate exti acts , pp. 1977-1981, copyright 1995, with permission from the American Chemical Society.

Cool surfaces (cool roofs and cool pavements) and urban trees can reduce urban air temperature and hence can reduce cooling-energy use and smog. A... 

Cannon, R. E. (1998). The Gas Processing Industry Origins and Evolution, 2nd ed. Tulsa Gas Processors Association. Delucclii, M. A. (1998). LPG for Motor Vehicles A Total Fuel Cycle Analysis of Emissions of Urban Air Pollutants and Greenhouse Gases, prepared for the Propane Vehicle Council and the Propane Education Research Council, Washington, DC. 

Sulfur dioxide emissions resulting from fossil fuel can have negative effects on urban air quality and create acid rain that harms aquatic life. These emissions arc nonexcludable in that there is no private action that a particular individual can take to avoid this impact, and they are nonrival in that their effect on any one individual does not preclude or offset their effect on any other. 

An average adult breathes about 8.50 X 103 L of air per day. The concentration of lead in highly polluted urban air is 7.0 X 10 6 g of lead per one m3 of air. Assume that 75% of die lead is present as particles less than 1.0 X 10 6 m in diameter, and that 50% of die particles below that size are retained in the lungs. Calculate the mass of lead absorbed in this manner in 1 year by an average adult living in this environment... 

Existence of the PSS was predicted theoretically by Leighton (61), and experimental studies of this relationship date back almost 20 years. These experiments have been accomplished in smog chambers (62), polluted urban air (63,64,65), rural environments (66), and in the free troposphere (67). The goal of these experiments has been to verify that our understanding of NOjj chemistry is fundamentally correct, and to ver the role of H02 and R02 in ozone formation. Studies in polluted air seem to confirm the dominance... 

Dicarbonyls. A third area of uncertainty is the treatment of dicarbonyls formed from aromatic or terpene hydrocarbon oxidation. (The simplest is glyoxal, CHOCHO, but a large number have been identified, 47. The yields and subsequent reactions of these compounds represent a major area of uncertainty in urban air photochemistry (186) and since they may be a significant source of HOjj through photolysis, inaccuracies in their portrayal may result in errors in calculated values of HO. and HO2.. 

AKLAND ET AL. Global Assessment of Ambient Urban Air Quality... 

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