18.104.22.168. Air Quality and Ground-Level Ozone
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
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 the San Francisco Bay area, maximum ozone concentration could increase
by about 20% and could approximately double the area that would be out of
compliance with the National Ambient Air Quality Standard (NAAQS).
- In New York, ground-level ozone concentrations could increase by 4%.
- In the Midwest and Southeast, changes in ground-level ozone levels could
range from a decrease of 2.4% to an increase of 8%, and the area in exceedance
of the ozone standard could exhibit nearly a threefold increase.
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).