Page 116 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

80 part I The energy–atmosphere System
Air pollution associated with coal-burning indus- tries is known as industrial smog (see Figure GIA 3.1). The term smog, mentioned earlier, was coined by a London physician in 1900 to describe the combination of fog and smoke containing sulfur gases (sulfur is an impurity in fossil fuels); in the case of industrial air pollution, the use of smog is correct.
Industrial pollution has high concentrations of carbon dioxide, particulates (discussed just ahead), and sulfur oxides. Once in the atmosphere, sulfur dioxide (SO2) re- acts with oxygen (O) to form sulfur trioxide (SO3), which is highly reactive and, in the presence of water or water vapour, forms tiny particles known as sulfate aerosols. Sulfuric acid (H2SO4) can also form, even in moderately polluted air at normal temperatures. Coal-burning electric utilities and steel manufacturing are the main sources of sulfur dioxide.
Sulfur dioxide–laden air is dangerous to health, corrodes metals, and deteriorates stone building ma- terials at accelerated rates. Sulfuric acid deposition, added to nitric acid deposition, has increased in se- verity since it was first described in the 1970s. Focus Study 3.2 discusses this vital atmospheric issue and recent progress.
Particulates/Aerosols The diverse mixture of fine particles, both solid and liquid, that pollute the air and affect human health is referred to as particulate matter (PM), a term used by meteorologists and regu- latory agencies such as the Meteorological Service of Canada and the U.S. Environmental Protection Agency. Other scientists refer to these particulates as aerosols. Examples are haze, smoke, and dust, which are vis- ible reminders of particulates in the air we breathe. Remote sensing now provides a global portrait of such aerosols—look ahead to the background image in The Human Denominator, Figure HD 3.
Black carbon, or “soot,” is an aerosol having devas- tating health effects in developing countries, especially where people burn animal dung for cooking and heat- ing. This fine particulate is not necessarily prevalent over urban areas; black carbon is mainly produced in small villages, but winds can spread it over the globe. In Africa, Asia, and South America, cooking stoves produce the highest concentrations, with diesel en- gines and coal plants having a smaller role. Black car- bon is both an indoor and outdoor pollutant, made up of pure carbon in several forms; it absorbs heat in the atmosphere and changes the reflectivity of snow and ice surfaces, giving it a critical role in climate change (dis- cussed in Chapter 4).
The effects of PM on human health vary with the size of the particle. PM2.5 is the designation for particu- lates 2.5 microns (2.5 μm) or less in diameter; these pose the greatest health risk. Sulfate aerosols are an example, with sizes about 0.1 to 1 μm in diameter. For comparison, a human hair can range from 50 to 70 μm in diameter.
These fine particles, such as combustion particles, organ- ics (biological materials such as pollens), and metallic aerosols, can get into the lungs and bloodstream. Coarse particles (PM10) are of less concern, although they can ir- ritate a person’s eyes, nose, and throat.
New studies are implicating even smaller particles, known as ultrafines at a size of PM0.1, as a cause of seri- ous health problems. These are many times more potent than the larger PM2.5 and PM10 particles because they can get into smaller channels in lung tissue and cause scarring, abnormal thickening, and damage called fi- brosis. Asthma prevalence has nearly doubled since 1980 in the United States, a major cause being motor vehicle–related air pollution—specifically, ozone, sulfur dioxide, and fine particulate matter.
Natural Factors That Affect Pollutants
The problems resulting from both natural and anthropo- genic atmospheric contaminants are made worse by sev- eral important natural factors. Among these, wind, local and regional landscape characteristics, and temperature inversions in the troposphere dominate.
Winds Winds gather and move pollutants, sometimes reducing the concentration of pollution in one location while increasing it in another. Dust, defined as particles less than 62 μm, is often moved by wind, sometimes in dramatic episodes. Dust can come from natural sources, such as dry lakebeds, or human sources, such as over- grazed or over-irrigated lands. Dust can be tracked by chemical analysis to determine its source areas.
Travelling on prevailing winds, dust from Africa contributes to the soils of South America and Europe, and Texas dust ends up across the Atlantic (Figure 3.6). Imagine at any one moment a billion tonnes of dust aloft in the atmospheric circulation, carried by the winds!
Winds make the atmosphere’s condition an inter- national issue. For example, prevailing winds transport air pollution from the United States to Canada, causing much complaint and negotiation between the two gov- ernments. Pollution from North America adds to Euro- pean air problems. In Europe, the cross-boundary drift of pollution is common because of the small size and prox- imity of many countries, a factor in the formation of the European Union (EU).
Arctic haze is a term from the 1950s, when pilots no- ticed decreased visibility, either on the horizon ahead or when looking down at an angle from their aircraft, across the Arctic region. Haze is a concentration of microscopic particles and air pollution that diminishes air clarity. Since there is no heavy industry at these high latitudes and only sparse population, this seasonal haze is the remarkable product of industrialization elsewhere in the Northern Hemisphere, especially Eurasia. Recent increases in wild- fires in the Northern Hemisphere and agricultural burning in the midlatitudes contribute to Arctic haze.