Projected climate changes could lead to exacerbation of respiratory disorders associated with reduced air quality in urban and rural areas and effects on the seasonality of certain allergic respiratory disorders.
It is well established that exposure to single or combined air pollutants has serious public health consequences. For example, ozone at ground level has been identified as causing damage to lung tissue, particularly among the elderly and children-reducing pulmonary function and sensitizing airways to other irritants and allergens (Beckett, 1991; Schwartz, 1994; U.S. EPA, 1996). Ground-level ozone affects not only those with impaired respiratory function, such as persons with asthma and chronic obstructive lung disease, but also healthy individuals. Even at relatively low exposure levels, healthy individuals can experience chest pain, coughing, nausea, and pulmonary congestion as a result of exposure to ground-level ozone.
Researchers also recognize that concurrent hot weather and air pollution can have synergistic impacts on health (Katsouyanni et al., 1993). For example, warmer temperatures can accelerate production and increase concentrations of photochemical oxidants in urban and rural areas and thus exacerbate respiratory disorders (Shumway et al., 1988; Schwartz and Dockery, 1992; Dockery et al., 1993; Katsouyanni et al., 1993; Pope et al., 1995; Phelps, 1996).
Few large-scale studies have been performed to assess the implications of climate change on air quality or population exposures to high concentrations of ground-level ozone. This limitation is related to difficulty in devising a defensible scenario of future climate change for a specific location, the previous focus on acute short-term effects rather than long-term effects, and the expense involved in modeling atmospheric chemistry. There is a limited number of studies, however, that shed some light on possible impacts of climate change on air quality and associated health implications.
Emberlin (1994), for example, has suggested that global warming may affect the seasonality of certain allergic respiratory disorders by altering the production of plant aero-allergens. Asthma and hay fever can be triggered by aero-allergens that cause high seasonal morbidity. The severity of allergies may be intensified by projected changes in heat and humidity, thereby contributing to breathing difficulties (Environment Canada et al., 1995; Maarouf, 1995).
Ozone concentrations at ground level continue to be the most pervasive air pollution problem in North America. The U.S. population exposed to unhealthy levels of ozone has fluctuated over the past 10-20 years-reaching a peak in 1988, when 112 million people lived in areas with higher than acceptable concentrations. In addition, recent studies (U.S. EPA, 1996) provide evidence of a positive correlation between ground-level ozone and respiratory-related hospital admissions in several cities in the United States. Such hospital admissions in the province of Ontario strongly relate to ambient levels of sulfur dioxide and ozone and to temperature (Canadian Public Health Association, 1992).
Research has shown that ground-level ozone formation is affected by weather and climate. Many studies have focused on the relationship between temperature and ozone concentrations (Wolff and Lioy, 1978; Atwater, 1984; Kuntasal and Chang, 1987; Wackter and Bayly, 1988; Wakim, 1989). For example, the large increase in ozone concentrations at ground level in 1988 in the United States and in parts of southern Canada can be attributed, in part, to meteorological conditions; 1988 was the third-hottest summer in the past 100 years. In general, the aforementioned studies suggest a nonlinear relationship between temperature and ozone concentrations at ground level: Below temperatures of 22-26°C (70-80°F), there is no relationship between ozone concentrations and temperature; above 32°C (90°F), there is a strong positive relationship.
Regression analyses have revealed that high temperatures are a necessary condition for high ozone concentrations at ground level; other meteorological variables often need to be considered, however. Weather variables that have been included in regression equations include temperature, wind speed, relative humidity, and sky cover (Wakim, 1990; Korsog and Wolff, 1991); however, other variables that could be included are wind direction, dew-point temperature, sea-level pressure, and precipitation.
Studies of ground-level ozone concentrations in which emissions and other weather factors are held constant (Smith and Tirpak, 1989) suggest the following impacts on ground-level ozone as a result of a 4°C warming:
In Canada, a projected fivefold rise in the frequency of hot days (i.e., those with temperatures >30°C) could lead to a greater number of days with levels of ground-level ozone considered to be a health risk for sensitive individuals in the population (Environment Canada et al., 1995).
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