Urbanization

The term bitumen is used in France to designate petroleum products, as in Great Britain and Germany. In the United States on the other hand, the equivalent material is designated by the expression asphalt-cement . In France, asphalt is a mastic, a mixture of bitumen and powdered minerals, poured in place. This mixture can be either natural or reconstituted by an industriai process. Asphait (French meaning) is utilized on roads, particularly in urban centers as well as for sidewalk surfacing. 

Dispersants are particularly important when engines operate below their normal operating temperature (as is the case of a short urban trip). Dispersants act by keeping oxidation products in suspension. 

Ecole Nationale Superieure du Petrole et des Moteurs Formation Industrie end point (or FBP - final boiling point) electrostatic precipitation ethyl tertiary butyl ether European Union extra-urban driving cycle volume fraction distilled at 70-100-180-210°C Fachausschuss Mineralol-und-Brennstoff-Normung fluid catalytic cracking Food and Drug Administration front end octane number fluorescent indicator adsorption flame ionization detector... 

Haider M, Rose H, Uhiemann S, Schwab E, Kabius B and Urban K 1998 A sphericai-aberration-corrected 200 keV transmission eiectron microscope Ultramicroscopy 75 53-60... 

Atmospheric corrosion results from a metal s ambient-temperature reaction, with the earth s atmosphere as the corrosive environment. Atmospheric corrosion is electrochemical in nature, but differs from corrosion in aqueous solutions in that the electrochemical reactions occur under very thin layers of electrolyte on the metal surface. This influences the amount of oxygen present on the metal surface, since diffusion of oxygen from the atmosphere/electrolyte solution interface to the solution/metal interface is rapid. Atmospheric corrosion rates of metals are strongly influenced by moisture, temperature and presence of contaminants (e.g., NaCl, SO2,. ..). Hence, significantly different resistances to atmospheric corrosion are observed depending on the geographical location, whether mral, urban or marine. 

If the normal carbonate is used, the basic carbonate or white lead, Pb(OH),. 2PbCO,. is precipitated. The basic carbonate was used extensively as a base in paints but is now less common, having been largely replaced by either titanium dioxide or zinc oxide. Paints made with white lead are not only poisonous but blacken in urban atmospheres due to the formation of lead sulphide and it is hardly surprising that their use is declining. 

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 ... 

In the fall of 1976 I had a call from a friend, Sid Benson, who, after a decade at the Stanford Research Institute, just returned to the University of Southern California (USC) in Los Angeles. He invited me for a visit, telling me about USC s plans to build up seleeted programs, ineluding chemistry. I visited USC and found it, with its close to downtown urban campus, quite different from the sprawling expanse of the eross-town eampus of UCLA, whieh I had visited on a number of oe-... 

I. Hubac, J. Masik, P. Mach, J. Urban, P. Babinec, Computational Chemistry Reviews... 

This paper describes the construction and use of a diffusion tube for sampling NO2 from the atmosphere. Examples of its use include the determination of NO2 concentrations at various heights above ground level in an urban environment and through a tree s leaf canopy. 

Total airborne particulates are determined using a high-volume air sampler equipped with either cellulose fiber or glass fiber filters. Samples taken from urban environments require approximately 1 h of sampling time, but samples from rural environments require substantially longer times. 

Manufactured Home Construction and Safety Standard Regulation 24CFR 3280.208, U.S. Department of Housing and Urban Development (HUD), Washington, D.C., Feb. 11, 1985. 

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

In a polluted or urban atmosphere, O formation by the CH oxidation mechanism is overshadowed by the oxidation of other VOCs. Seed OH can be produced from reactions 4 and 5, but the photodisassociation of carbonyls and nitrous acid [7782-77-6] HNO2, (formed from the reaction of OH + NO and other reactions) are also important sources of OH ia polluted environments. An imperfect, but useful, measure of the rate of O formation by VOC oxidation is the rate of the initial OH-VOC reaction, shown ia Table 4 relative to the OH-CH rate for some commonly occurring VOCs. Also given are the median VOC concentrations. Shown for comparison are the relative reaction rates for two VOC species that are emitted by vegetation isoprene and a-piuene. In general, internally bonded olefins are the most reactive, followed ia decreasiag order by terminally bonded olefins, multi alkyl aromatics, monoalkyl aromatics, C and higher paraffins, C2—C paraffins, benzene, acetylene, and ethane. 

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). 

Fig. 5. Size distributions of atmospheric particles ia (—) urban, (------) mral, and (------) remote background areas.

Table 5. Summary of Detailed Particulate Measurements at Urban and Rural Locations...

Catching Our Breath. Next Steps forKeducing Urban O ne, U.S. Office of Technology Assessment, Washington, D.C., 1989, pp. 101—102. 

C. M. Urban, T. J. Timbario, and R. L. Bechtold, "Performance and Emissions of a DDC 8V-71 Engine Pueled with Cetane Improved Methanol," SyPE Paper 892064, SyPE Int. Fuels and Eubricants Meeting and Expo. (Baltimore, Md., Sept. 25—28,1989) Society of Automotive Engineers, Warrendale, Pa. 

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. 

Anhydrous, monomeric formaldehyde is not available commercially. The pure, dry gas is relatively stable at 80—100°C but slowly polymerizes at lower temperatures. Traces of polar impurities such as acids, alkahes, and water greatly accelerate the polymerization. When Hquid formaldehyde is warmed to room temperature in a sealed ampul, it polymerizes rapidly with evolution of heat (63 kj /mol or 15.05 kcal/mol). Uncatalyzed decomposition is very slow below 300°C extrapolation of kinetic data (32) to 400°C indicates that the rate of decomposition is ca 0.44%/min at 101 kPa (1 atm). The main products ate CO and H2. Metals such as platinum (33), copper (34), and chromia and alumina (35) also catalyze the formation of methanol, methyl formate, formic acid, carbon dioxide, and methane. Trace levels of formaldehyde found in urban atmospheres are readily photo-oxidized to carbon dioxide the half-life ranges from 35—50 minutes (36). 

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