SO2 affects people quickly, usually within the first few minutes of exposure. Epidemioloogical studies indicate that SO2 exposure can lead to the kind of acute health effects typical of particulate pollution. Exposure is linked to an increase in hospitalizations and deaths from respiratory and cardiovascular causes, especially among asthmatics and those with preexisting respiratory diseases (15)(16)(17)(18). The severity of these effects increases with rising SO2 levels, and exercise enhances the severity by increasing the volume of SO2 inhaled and allowing SO2 to penetrate deeper into the respiratory tract (19). Asthmatics may experience wheezing and other symptoms at much lower SO2 levels than those without asthma. When ozone pollution is also present, asthmatics become even more sensitive to SO2 a good reminder that air pollutants generally do not occur in isolation, but in complex mixtures that create the potential for synergistic effects among pollutants (20)(21).
Ground-level ozone is the major component of the photochemical smog that blankets many urban areas. It is not emitted directly but is formed when nitrogen oxides from fuel combustion react with so-called volatile organic compounds (VOCs) such as unburned gasoline or paint solvents in the atmosphere. sunlight and heat stimulate ozone formation, so peak ozone levels generally occur in the summer.
Ozone pollution has become widespread in cities in Europe, North America, and Japan as auto and industrial emissions have increased. Many cities in developing countries also suffer from high ozone levels, although few monitoring data exist (22)(23).
A powerful oxidant, ozone can react with nearly any biological tissue. Breathing ozone concentrations of 0.012 ppm levels typical in many cities can irritate the respiratory tract and impair lung function, causing coughing, shortness of breath, and chest pain. Exercise increases these effects, and heavy exercise can bring on symptoms even at low ozone levels (0.08 ppm). Evidence also suggests ozone exposure lowers the body’s defenses, increasing susceptibility to respiratory infections (24)(25).
As ozone levels rise, hospital admissions and emergency room visits for respiratory illnesses such as asthma also increase. On average, studies show that hospital admissions rise roughly 7 to 10 percent for a 0.05 ppm increase in ozone levels. In its recent analysis of ozone health impacts in 13 cities where ozone levels exceeded U.S. air standards, the American Lung Association estimated that high ozone levels were responsible for approximately 10,000 to 15,000 extra hospital admissions and 30,000 to 50,000 additional emergency room visits during the 1993-94 ozone season (26)(27).
References and notes
20. Lawrence Folinsbee, “Human Health Effects of Air Pollution,” Environmental Health Perspectives, Vol. 100 (1992), pp. 47-48.
21. Derek Elsom, Smog Alert: Managing Urban Air Quality (Earthscan Publications Limited, London, 1996), p. 48.
22. Op. cit. 1, p. 3.
23. World Health Organization and the United Nations Environment Programme, Urban Air Pollution in Megacities of the World (Blackwell Publishers, Oxford, UK, 1992), pp. 10-11.