Factors That Contribute to Human Population Growth
Although it is apparent that population growth must be controlled, population trends are difficult to influence and manage. A variety of interconnecting factors fuel the current population explosion:
• High fertility rates: The combination of poverty, very high child mortality rates, and a lack of social provisions of every type is associated with high fertility rates in the developing world. Families have many children to ensure that enough survive childhood to work for the household and to care for parents in old age. Most countries, both developed and developing, have experienced significant reductions in fertility as contraceptive use has increased. However, the majority of developing countries still have fertility levels that ensure substantial population growth. In a small number of countries, most of which are classified as least developed, fertility levels continue to be very high.
• Lack of family planning resources: Half the world’s couples don’t use any form of family planning.
• Lower death rates: Although death rates remain relatively high in the developing world, they have decreased in recent years because of public health measures and improved medical care.
Changes in any of these factors can affect population growth, but the issues are complex. Increasing death rates through disease, famine, or war might slow population growth, but few people would argue in favor of these as methods of population control. Although the increased availability of family planning services is a crucial part of
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AIR QUALITY AND POLLUTION
Air pollution is not a human invention or even a new problem. The air is polluted naturally with every forest fire, pollen bloom, and dust storm, as well as with countless other natural pollutants. To these natural sources, humans have always contributed the by-products of our activities.
Air pollution is linked to a wide range of health problems, and the very young and the elderly are among the most susceptible to air pollution’s effects. For people with chronic ailments such as diabetes or heart failure, even relatively brief exposure to particulate air pollution increases the risk of death by nearly 40%. Recent studies have linked exposure to air pollution to reduced birth weight in infants, reduced lung capacity in teens, and atherosclerosis (thickening of the arteries) in adults.
Air Quality and Smog
The U.S. Environmental Protection Agency (EPA) uses a measure called the Air Quality Index (AQI) to indicate whether air pollution levels pose a health concern. The AQI is used for five major air pollutants:
• Carbon monoxide (CO): An odorless, colorless gas, CO forms when the carbon in fossil fuels does not completely burn. The primary sources of CO are vehicle exhaust and fuel combustion in industrial processes. CO deprives body cells of oxygen, causing headaches, fatigue, and impaired vision and judgment. It also aggravates cardiovascular diseases.
• Sulfur dioxide (SO2): SO2 is produced by the burning of sulfur-containing fuels such as coal and oil, during metal smelting, and by other industrial processes; power plants are a major source. In humans, SO2 narrows the airways, which may cause wheezing, chest tightness, and shortness of breath, particularly in people with asthma. SO2 may also aggravate symptoms of CVD.
• Nitrogen dioxide (NO2): NO2 is a reddish-brown, highly reactive gas formed when nitric oxide combines with oxygen in the atmosphere; major sources include motor vehicles and power plants. In people with respiratory diseases such as asthma, NO2 affects lung function and causes symptoms such as wheezing and shortness of breath. NO2 exposure may also increase the risk of respiratory infections.
• Particulate matter (PM): Particles of different sizes are released into the atmosphere from a variety of sources, including combustion of fossil fuels, crushing or grinding operations, industrial processes, and dust from roadways. PM can accumulate in the respiratory system, aggravate cardiovascular and lung diseases, and increase the risk of respiratory infections.
• Ground-level ozone: At ground level, ozone is a harmful pollutant. Where it occurs naturally in the upper atmosphere, it shields the earth from the sun’s harmful ultraviolet rays. (The health hazards from the thinning of this protective ozone layer are discussed later in the chapter.) Ground-level ozone is formed when pollutants emitted by cars, power plants, industrial plants, and other sources react chemically in the presence of sunlight (photochemical reactions). Ozone can irritate the respiratory system, reduce lung function, aggravate asthma, increase susceptibility to respiratory infections, and damage the lining of the lungs. Short-term elevations of ozone levels have also been linked to increased death rates.
AQI values run from 0 to 500; the higher the AQI, the greater the level of pollution and associated health danger. When the AQI exceeds 100, air quality is considered unhealthy, at first for certain sensitive groups of people and then for everyone as AQI values get higher. For local areas, AQI values are calculated for each of the five pollutants listed above, and the highest value becomes the AQI rating for that day. Depending on the AQI value, local officials may issue precautionary health advice. Local AQI information is often available in newspapers, on television and radio, on the Internet, and from state and local telephone hotlines.
The term smog was first used in the early 1900s in London to describe the combination of smoke and fog. What we typically call smog today is a mixture of pollutants, with ground-level ozone being the key ingredient. Major smog occurrences are linked to the combination of several factors: Heavy motor vehicle traffic, high temperatures, and sunny weather can increase the production of ozone. Pollutants are also more likely to build up in areas with little wind and/or where a topographic feature such as a mountain range or valley prevents the wind from pushing out stagnant air.
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