Chapter 2.doc

Chapter 2: Urban and Transboundary Air Pollution: • As a result of epidiemics, scientisits increased attention to the health effects of air pollution- identifiying specific pollutant sources and their transport in the atmosphere, elucidating exposure-response relationships. • These crisis have several aspects: first since the atmosphere is dynamic and always changing, contaminants are transported, diluted precipitated and transformed. • Second, the primary emission of sulphur oxides, nitrogen oxides, carbon monoxide, resporable particulates and metals are severely polluting cities and twon in asia, Africa and Latin eastern Europe. • Poor countries had higher level of total suspended particulates then wealthier countires • Third in nations, that have reduced the primary emissions from heavy industry, power plants and automobiles, new problems have arisen from air pollution contribute to heavily to the high mortality rates observed from acute respiratory disease. • Defining adverse health effects: • Any effect that results in altered structure or impaired function or that represents the beginning of a sequence of events leading to altered structure or function is considered an “adverse health effect” • Specific air pollutants associated with adverse respiratory effects: • Several types of air pollution are currently recognized to cause adverse respiratory health effects: sulphur oxides and acidic particulate complexs, photochemical oxidants, and a miscellaneous category of pollutants arising from industrial sources. • Sulphur dioxide and acidic aerosols: • Sulfur dioxide is produced by the combustion of sulphur contained in fossil fuels, such as coals and crude oil. • The major sources of environmental pollution with sulphur dioxide are electric power generating plants, oil refineries, and smelters. • Slufor dioxide is a clear, highly water soluble gas, so it is effectively absorbed by mucous membranes of the upper airways, with a much smaller portion reacting the distal regions of the lung. • The sulphur dioxide released into the atmosphere does not remain gaseous. It undergoes chemical reaction with water, metals and other pollutants to form aerosols. • Sulphur dioxide therefore, together with other products of fossil fuel combustion forms the heavy urban pollution. • Smog a descriptive term generally referring to the visibly cloudy combination of smoke and fog—an acidic aerosol is formed that has been shown to induce asthematic responses in both adults and children. • The havard six citities study demonstrated a significant association between chronic cough and bronchitis and hydrogen ion concentration- a measure of acidity- rather than sulphate levels or total particulate levels. • Two measures of air acidity showed significant effects • Higher particle acidity was significantly associated with an increased risk of bronchitis, while higher levels of gasoues acids were also positively associated with wheeze attacks, chronic wheezing and any asthmatic symptoms. • A time series analysis that examined mortality and morbidity in buffalo showed signficnant positive association between aerosol acidity and increased respiratory hospital admission and respiratory mortality • Several studies linked exposure to acidic aerosols and mortality, documenting an increase in deaths of persons with underlying chronic heart and lung disease who had been exposed. • Acidic aerosols results in acid rain, which may threaten aquatic life. • In addition to the acute bronchoconstrictive effects of sulphur dioxide, there is epidemiologic evidence for chronic airway obstruction in persons exposed to elevated levels of SO2. • Particulates: • Particulate air pollution is closely related to SO and aerosols. 2 • The term usually refers to particles suspended in the air after various forms of combustion or other industrial activity. • The air pollution was characterized by high levels of particulates, sulphur dioxide, and moisture. • Schwartz and Neas found that increases in fine particles were significantly associated with respiratory symptoms and decrements in peak flow measurements: • There is evidence that reduced HR V is a risk factor for adverse cardiac events,