Frumkin, 2e Part Three: Environmental Health on the Regional Scale. Chapter 12: Air Pollution

Transcription

1 Frumkin, 2e Part Three: Environmental Health on the Regional Scale Chapter 12: Air Pollution

2 History of Air Pollution Since human beings discovered fire, they began to pollute the air. At first, air pollution was a local problem resulting from the smoke from kilns, hearths, and furnaces. However, with the rise of industrialization and the development of time, air pollution has become a global problem. It came to the forefront of public attention in the form of severe and fatal episodes, such as that of Donora, PA and the Meuse Valley in Belgium.

3 Types of Ambient Air Pollution Air pollutants can be categorized by their source or by their physical and chemical characteristics. An air pollutant may be either directly emitted (a primary pollutant) or formed in the atmosphere through the physical and chemical conversion of precursors (a secondary pollutant). Another important feature of air pollution sources is whether the emissions are natural (biogenic) or the result of human activity (anthropogenic). Additionally, air pollutants differ in their physical form; they can be either gases or particles. A final way of classifying air pollutants relates to the way they are legally regulated. Some are criteria pollutants (the major pollutants, including carbon monoxide, lead, nitrogen, etc.), and others are hazardous air pollutants, which include a number of volatile organic chemicals, pesticides, herbicides, and radionuclides.

4 Studies on Air Pollution and Health Epidemiological studies investigate the relationship between air pollutant concentrations and health outcomes under the real-world conditions of exposure, typically in large populations in community settings. Herein, data on pollutant concentrations are obtained by air monitoring, and used as measures of individual exposure. However, epidemiological studies can potentially be limited by the inability to control for other factors, referred to as confounding factors, such as temperature, weather, population characteristics, and pollutants other than those being investigated, and by the difficulty of accurately estimating personal exposure. Controlled human exposure studies correct for possible confounds, and involve exposure of volunteers to a specified concentration of a particular air pollutant or pollutant mixture in a laboratory setting and then measurements of their health responses.

5 Sources of Air Pollution There are many sources of air pollution, including particulate matter, sulfur dioxide, nitrogen oxides, volatile organic compounds, tropospheric ozone, carbon monoxide, lead, and mercury.

6 Particulate Matter Particulate matter (PM) refers to a generic class of pollution rather than to a particular, individual pollutant with a specified chemical structure. PM includes solid or liquid particles suspended in air, regardless of their chemical composition. The composition of PM differs by geographic area and can vary with season, source, and meteorology.

7 Particulate Matter, con t Particles are generally categorized according to their size, using a measure called aerodynamic diameter. This is the diameter of a uniform sphere of unit density that would attain the same terminal settling velocity as the particle of interest. Ambient levels of PM, have been associated with health effects including increased hospital and emergency room admissions, respiratory symptoms, decline in pulmonary function, exacerbation of chronic respiratory and cardiovascular diseases, and premature mortality.

8 Sulfur Dioxide Sulfur dioxide, SO 2, is a water-soluble gas that is produced from the combustion of sulfur-containing fuels and materials, such as coal and metal ores. SO 2 can be converted to sulfuric acid, and therefore contributes to acid deposition, which harms vegetation, other materials, and wildlife. SO 2 also contributes to the formation of particulate matter. Because SO 2 is highly soluble in water, most inhaled SO 2 is absorbed by the mucous membranes of the upper airways with little reaching the lung. SO 2 exposure has been associated with reduced lung function, bronchoconstriction (increased airway resistance), respiratory symptoms, hospitalizations from cardiovascular and respiratory causes, eye irritation, adverse pregnancy outcomes, and mortality.

9 Nitrogen Oxides Nitrogen oxides, NOx, make up a category of highly reactive gases containing nitrogen and oxygen, such as nitrogen dioxide (NO 2 ) and nitrogen oxide (NO). NOx are produced through combustion, including fossil fuel combustion, when the nitrogen that constitutes almost 80 percent of air is oxidized. Like ozone, NO 2 is nearly insoluble in water and can reach the lower respiratory tract. Health effects of NO 2 include irritation of the eyes, nose, and throat at higher concentrations; short-term decreases in lung function; and possibly increased respiratory infections and symptoms for children.

10 Volatile Organic Compounds Volatile organic compounds (VOCs) are a category of organic chemicals with a high vapor pressure, which readily evaporate at normal temperature and pressure. They include benzene, chloroform, formaldehyde, isoprene, methanol, monoterpenes, and hundreds of additional compounds. VOCs originate from natural sources (primarily vegetation such as oak and maple trees); industrial processes involving such things as chemical processing, use of solvents, and power generation; and transportation, including motor vehicles and off-road transportation sources such as aircraft, construction equipment, and lawn mowers. VOCs are precursors of ozone but also have independent health effects, including irritation of the respiratory tract, headaches, and carcinogenicity.

11 Tropospheric Ozone Ozone (O 3 ), a gas, is present in the troposphere, the lowest atmospheric layer, which extends from the Earth s surface to the stratosphere. Stratospheric ozone forms the naturally occurring ozone layer that protects us from ultraviolet radiation, whereas tropospheric ozone, sometimes called ground-level ozone, is a harmful pollutant. Tropospheric ozone is a colorless gas and a photochemical oxidant formed through complex, nonlinear chemical reactions involving the precursors VOCs and NOx in the presence of sunlight. Ozone is not highly soluble in water and can thus reach the lower respiratory tract.

12 Ozone, con t Because of its oxidant properties, ozone can break molecular bonds and rapidly damage human tissue. Short-term exposure to ozone for healthy adults has been associated with temporarily decreased lung function, increased airway resistance, and increased respiratory symptoms, such as coughing and wheezing. Asthmatics are particularly susceptible to health problems associated with ozone exposure.

13 Carbon Monoxide Carbon monoxide (CO) is a colorless, odorless gas formed by incomplete combustion of carbonaceous material, such as gasoline, natural gas, oil, coal, tobacco, and other organic materials. When CO is inhaled, it binds to hemoglobin, with over 200 times the affinity of oxygen, to form carboxyhemoglobin (COHb). An increased level of COHb reduces the transport of oxygen to tissues and inhibits the release of oxygen, causing problems in the brain, heart, and respiratory system.

14 Lead Historically, lead in ambient air came largely from leaded fuel, that is, fuel with lead added as an antiknocking agent. Most countries have already phased out leaded gasoline or have plans to do so. In these areas, nonairborne sources of lead, such as ingestion of leaded paint, are a larger health concern than airborne lead. Lead can be harmful even at low doses because it accumulates in the body, mostly in the bones. Exposure to lead can cause damage to the nervous system and kidneys and can interfere with red blood cell formation, reproductive function, and gastrointestinal function.

15 Mercury Mercury is naturally occurring, but can be released into the atmosphere, soil, or water through human activities. Because mercury commonly contaminates coal, coal-fired power plants are the largest source of airborne mercury in the United States. Mercury exposure can occur through inhalation, skin contact, or ingestion, and the health effects of mercury depend on its chemical form. Mercury can be deposited into water bodies and consumed by fish, presenting the problem of exposure through food intake.

16 Air Toxics Hundreds of other ambient air pollutants exist besides those just described. They include hydrochloric acid, captan, parathion, naphthalene, biphenyl, vinyl bromide, methyl bromide, dioxin, and cadmium. Exposure to these pollutants can occur through inhalation, but they also enter other environmental media such as water and food. Health effects of these air toxics include damage to the neurological, immune, respiratory, and reproductive (for example, reduced fertility) systems, as well as developmental problems and some cancers.

17 Air Pollution Prevention And Control Air quality management approaches include controlling emissions at the source, by such means as scrubbers at coal-fired power plants; reducing the volume of emissions, by such means as increased use of public transportation to lower vehicular air pollutants or emissions controls for automobiles; and decreasing population exposure. Reduction of the health effects of air pollution comes from actions at multiple spatial and institutional levels, ranging from personal decisions by individuals, to community and state plans, and to multigovernment agreements.