Brown smog

This dimerization is not unexpected, since N02 has one unused valence electron left on the N. Reaction 8.14 is exothermic, so that the NO2/N2O4 mixture is browner at high temperature and at high dilutions. In high concentrations near room temperature, it is more yellow. The brown smog layers often seen over cities are due primarily to dilute N02, with some contribution from particulate matter. 

Particles are the major cause of the ha2e and the brown color that is often associated with smog. The three most important types of particles produced in smog are composed of organics, sulfates, and nitrates. Organic particles are formed when large VOC molecules, especially aromatics and cycHc alkenes, react with each other and form condensable products. Sulfate particles are formed by a series of reactions initiated by the attack of OH on SO2 in the gas phase or by Hquid-phase reactions. Nitrate particles are formed by... 

Smog over New York City. From a distance, you can clearly see die layer of smog containing reddish-brown nitrogen dioxide. 

Nitrogen dioxide, N02 (oxidation number -t-4), is a choking, poisonous, brown gas that contributes to the color and odor of smog. The molecule has an odd number of electrons, and in the gas phase it exists in equilibrium with its colorless dimer N204. Only the dimer exists in the solid, and so the brown gas condenses to a colorless solid. When it dissolves in water, NOz disproportionates into nitric acid (oxidation number +5) and nitrogen oxide (oxidation number +2) ... 

In NO, smog formation (NO, is a mixture of NO, N2O, NO2, N2O4, and N2O5) the NO is produced by reaction of N2 and O2 at the high temperatures of combustion in automobiles and fossil fuel power plants, and NO2 and the other NO, species are produced by subsequent low-temperature oxidation of NO in air. NO is colorless, but NO2 absorbs visible radiation and produces brown haze. We write these reactions as a set of two reactions among four species,... 

Photochemical smog contains N02, the gas responsible for the brown blanket over larger cities. This gas can produce a dimer (two identical units chemically bonded) by the reaction, 2N02 —> N204. If the reaction of 750 g N02 goes all the way to the right, what will be the pressure in a 10-L chamber at 42°C ... 

Photochemistry, chemistry caused by light, is responsible for many of the atmospheric reactions that determine the quality of our air. Photochemical smog is the name given to the red-brown haze that can form over cities under certain weather conditions. Nitrogen (as N2) and oxygen... 

Oxidation of nitric oxide in smog gives nitrogen dioxide (Box 3.6), which is a brown gas. This colour means that it absorbs light and is photochemically active and undergoes dissociation ... 

Nitrogen dioxide, NO2, is a red-brown gas that contributes to the brown haze associated with smog. 

London smog was an object of fascination. A recent study explains artistic depictions of the murk—by painter Claude Monet and a multitude of writers—through the chemistry of coal tar, the source of the dye chemicals that were so important to the early study of environmental cancer. The yellow morning fog, Oscar Wilde s ochre-coloured hay, was tinted by tars in the smoke of household coal furnaces that burned at low temperature. By afternoon, the dark smoke from hotter-burning industrial furnaces would turn the smog to brown or black.3... 

Snyder, Death-Dealing Smog, pp. 22-28 D. Davis, When Smoke Ran Like Water (Basic Books, 2002), pp. 5-18 B. Roueche, Eleven Blue Men (Little Brown, Boston, 1953), pp. 194-211. 

Identify the gas that is responsible for the brown color of photochemical smog. 

Nitrogen dioxide (which causes the brown color of smog) then reacts with water to form nitric acid ... 

Nitrogen dioxide is present in the combustion discharges from industrial furnaces, building heating systems, and motor vehicles. It is a reddish-brown gas with an irritating odor, and has been associated with respiratory disease. It is also involved in the production of smog. 

Smog color is derived in part from suspended particulate matter. When smog is light brown, the eolor derives from nitrogen oxides. All of the other air pollutants listed are colorless. The answer is (D). 

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