Urban Air Pollution - Cambridge University Press Urban Air Pollution Anthropogenic air pollution has

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  • Chapter 4

    Urban Air Pollution

    Anthropogenic air pollution has affected the environ-

    ment since the development of the first human com-

    munities. Today, pollution arises due to the burning

    of wood, vegetation, coal, natural gas, oil, gasoline,

    kerosene, diesel, liquid biofuels, waste, and chemicals.

    Two general types of urban-scale pollution were iden-

    tified in the twentieth century: London-type smog and

    photochemical smog. The former results from the burn-

    ing of coal and other raw materials in the presence of

    a fog or strong temperature inversion, and the latter

    results from the emission of hydrocarbons and oxides

    of nitrogen in the presence of sunlight. In most places,

    urban air pollution consists of a combination of the two.

    In this chapter, urban outdoor gas-phase air pollution is

    discussed in terms of its history, early regulation, and

    chemistry.

    4.1. History and Early Regulation of Outdoor Urban Air Pollution

    Before the twentieth century, air pollution was treated

    as a regulatory or legal problem rather than a scientific

    problem. Because regulations were often weak or not

    enforced and health effects of air pollution were not well

    understood, pollution problems were rarely mitigated.

    In this section, a brief history of air pollution and its

    regulation until the 1940s is discussed.

    4.1.1. Before 1200: Metal Smelting and Wood Burning

    Available data suggest that air pollution in ancient

    Greece and the Roman Empire was likely severe due

    both to metal production and wood burning. From

    500 BC to 300 AD, lead concentrations in Greenland

    ice cores were four times their natural values. These

    concentrations were due to the transport of pollution

    from Greek and Roman lead and silver mining and

    smelting operations (Hong et al., 1994). Lead emis-

    sions in ancient Greece occurred predominantly from

    smelting during the production of silver coins. Each

    gram of silver resulted in ∼300 g of lead by-product.

    Lead emissions rose further during the Roman Empire

    because the Romans used lead in cookware, pipes,

    face powders, rouges, and paints. Cumulative lead

    pollution from smelting reaching Greenland between

    500 BC and 300 AD was about 15 percent of that

    from leaded gasoline worldwide between 1930 and

    1990.

    Whereas the Romans mined up to 80,000 to 100,000

    tonnes/yr of lead, they also mined 15,000 tonnes/yr of

    copper, 10,000 tonnes/yr of zinc, and 2 tonnes/yr of

    mercury (Nriagu, 1996). Ores containing these metals

    were smelted in open fires, producing pollution that was

    transported locally and long distances. For example,

    as evidenced by Greenland ice core data, the smelting

    of copper to produce coins during the Roman Empire

    and in China during the Song Dynasty (960–1279)

    increased atmospheric copper concentrations (Hong

    et al., 1996).

    However, pollution in Rome was due to both metal

    smelting and wood burning. The Roman poet Horace

    noted thousands of wood-burning fires (Hughes, 1994)

    and the blackening of buildings (Brimblecombe, 1999).

    Air pollution events caused by emissions under strong

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  • 74

    inversions in Rome were called “heavy heavens”

    (Hughes, 1994).

    Air pollution control in ancient Greece and Rome

    was relatively weak. In ancient Greece, town leaders

    were responsible for keeping sources of odors outside

    of town. In Rome, air pollution resulted in civil lawsuits.

    During the fall of the Roman Empire, lead smel-

    ter emissions declined significantly. Such emissions

    rebounded, however, c. 1000 AD, following the dis-

    covery of lead and silver mines in Germany, Aus-

    tria, Hungary, and other parts of central and eastern

    Europe (Hong et al., 1994). The discovery of these

    mines resulted in the movement of lead pollution from

    southern to central Europe. Wood burning, though, con-

    tinued throughout the decline of the Roman Empire in

    all population centers of the world.

    4.1.2. 1200–1700: Quicklime Production and Coal Burning

    In London during the Middle Ages, a new source of

    pollution was the production of quicklime [CaO(s), cal-

    cium oxide] to form a building material. Quicklime

    was produced by the heating of limestone [which con-

    tains calcium carbonate, CaCO3(s)] in kilns with oak

    brushwood as the primary fuel source. Quicklime was

    then mixed with water to produce a cement, slaked

    lime [calcium hydroxide, Ca(OH)2(s)], a building mate-

    rial. This process released organic gases, nitric oxide,

    carbon dioxide, and organic particulate matter into

    the air.

    Sea coal was introduced to London by 1228 and grad-

    ually replaced the use of wood as a fuel in lime kilns

    and forges. Wood shortages may have led to a surge in

    sea coal use by the mid-1200s. The burning of sea coal

    resulted in the release of sulfur dioxide, carbon diox-

    ide, nitric oxide, soot, and particulate organic matter.

    Coal merchants in London worked on Sea Coal Lane,

    and they would sell their coal to limeburners on nearby

    Limeburner’s Lane (Brimblecombe, 1987). The ratio of

    coal burned per forge to that burned per lime kiln may

    have been 1:1,000.

    The pollution in London due to the burning of sea

    coal became sufficiently severe that a commission was

    ordered by King Edward I in 1285 to study and remedy

    the situation. The commission met for several years,

    and finally, in 1306, the king banned the use of coal

    in lime kilns. The punishment was “grievous ransom,”

    which may have meant fines and furnace confiscation

    (Brimblecombe, 1987). One person may have been con-

    demned to death because he violated the law three times

    (Haagen-Smit, 1950). However, by 1329, the ban had

    either been lifted or lost its effect.

    Between the thirteenth and eighteenth centuries, the

    use of sea coal and charcoal increased in England. Coal

    was used not only in lime kilns and forges, but also

    in glass furnaces, brick furnaces, breweries, and home

    heating. One of the early writers on air pollution was

    John Evelyn (1620–1706), who wrote Fumifugium or

    The Inconveniencie of the Aer and the Smoake of Lon-

    don Dissipated in 1661. He explained how smoke in

    London was responsible for the fouling of churches,

    palaces, clothes, furnishings, paintings, rain, dew, water,

    and plants. He blamed “Brewers, Diers, Limeburners,

    Salt and Sope-boylers” for the problems.

    4.1.3. 1700–1840: The Steam Engine

    Air quality in Great Britain (the union of England, Scot-

    land, and Wales) increased by orders of magnitude in

    severity during the eighteenth century due to the inven-

    tion of the steam engine, a machine that burned coal

    to produce mechanical energy. The idea for the steam

    engine originated with the French-born English physi-

    cist Denis Papin (1647–1712), who invented the pres-

    sure cooker in 1679 while working with Robert Boyle.

    In this device, water was boiled under a closed lid.

    The addition of steam (water vapor at high tempera-

    ture) to the air in the cooker increased the total air

    pressure exerted on the cooker’s lid from within. Papin

    noticed that the high pressure pushed the lid up. The

    phenomenon gave him the idea that steam could be used

    to push a piston up in a cylinder, and the movement of

    the cylinder could be used to do work. Although he

    designed a model of such a cylinder-and-piston steam

    engine in 1690, Papin never built one.

    Capitalizing on the idea of Papin, Thomas Savery

    (1650–1715), an English engineer, patented the first

    practical steam engine in 1698. It replaced horses as a

    source of energy to pump water out of coal mines. The

    engine worked when water was boiled in a boiler to

    produce vapor that was transferred to a steam chamber.

    A pipe from the steam chamber to the water source in the

    mine was then opened. Liquid water was sprayed on the

    hot vapor in the steam chamber to recondense the vapor,

    creating a vacuum that sucked the water from the mine

    into the steam chamber. The pipe from the chamber to

    the mine was then closed, and another pipe from the

    chamber to outside the mine was opened. Finally, the

    boiler was fired up again to produce more water vapor

    to force the liquid water from the steam chamber out of

    the mine through the second pipe.

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