Effects of Air Pollution on Your Health

Air Pollution And Health:
The Ozone And Particulate Story

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Are ozone and particulates in the air from air pollution caused by fossil fuel burning dangerous to your health? Do you live in an urban setting and exposure to the outside air during hot summer days causes your eyes to burn and chest to tighten?

These symptoms are caused primarily by exposure to ozone in the summertime air. The hot temperatures and stale air in the summer in combination with urban air pollution furnish ideal conditions for the formation of ozone. For the most part, ozone forms from the interaction of nitrogen oxides emitted from motor vehicles, power plants, and industrial facilities and volatile organic compounds from spray painting, refueling of vehicles, road paving, and numerous other activities. Sunlight provides the catalyst for this reaction. Large urban areas have a higher levels of ozone formed due to greater amounts of smog associated with the aggregation of people and air pollution-producing activities. Due to its hot arid climate, its geological features, and the large number of people, the Los Angeles metro area is consistently plagued with higher ozone levels than the rest of the nation. However, several other large metropolitan areas in the U.S. also have severe ozone problems as indicated in the U.S. EPA's National Air Quality and Emissions Trend Report for 1993.

Ozone is a strong irritant of the mucus membranes, especially the respiratory tract. It causes constriction of the airways which makes breathing difficult and produces coughing, wheezing, and shortness of breath. Ozone can also be involved in the development of asthma. Lastly, it increases the vulnerability of the lungs to infection. Those particularly susceptible to adverse effects from exposure to ozone include young children, the elderly, and people with asthma, chronic bronchitis, or emphysema. However, adverse effects are not confirmed to this sensitive population. Even healthy adults may experience such symptoms if a lot of time is spent outdoors or vigorous exercise is carried out during periods of high ozone levels. The irritation caused by ozone may be further aggravated by other air pollutants like the sulfur dioxide produced by fossil fuel combustion from motor vehicles, homes, power plants, and industry.

Since ozone is a major air pollutant having negative impact on human health, the U.S. EPA has set a National Ambient Air Quality Standard (NAAQS) of 0.12 parts per million in the ambient air for a one hour time period. Based on 1993, it is estimated that 51 million Americans live in locations where ozone levels exceed the EPA's present standard. Based on the results of recent research indicating negative health impacts at lower levels, the EPA is considering lowering the present standard.

A number of studies, such as the The Six Cities Study explored the associations between air pollution produced by fossil fuel and adverse respiratory health in adults and children between 1974 and 1989. These studies were initiated after the Middle East oil embargo in the early 1970s forced power plants in the U.S.A. to burn more high sulfur coal.

Particulate air pollution was associated with increased cough, bronchitis and chest illness among the sampled children. There was some suggestion that lung function was lower in children living in communities with higher particulate levels. The follow-up of these children and adults over 12 years showed that defects in lung function persisted into adulthood and potentially put these children at increased risk of developing chronic obstructive pulmonary disease later in life. A recent analysis of the follow-up of the Six Cities Study adult sample showed that the mortality rate in adults increases by about 26% with exposure to inhalable particulate concentrations, especially the fine particulate fraction, such as smoke and soot (produced by industrial and automobile emissions). In a comparison of individuals living in the six U.S. communities, those in the most polluted cities had a 26% greater mortality rate than individuals living in the least polluted cities. This translates into a two-year shorter life for an individual living in the most polluted cities, a significant public health finding.

The findings of increased bronchitic illness in children with fine particles were followed by the "Twenty-Four Cities Study," of 15,000 children in suburban and rural communities in the U.S.A. and Canada. This study was initiated in response to an RFA focused on Acid Aerosols (1987) and designed to test the hypothesis that acid particulate matter produced from fossil- fueled power plants was responsible for the increased respiratory illness and lower lung function in children, which showed the highest acid particle concentration in the U.S. downwind of the major sulfur emissions in the Midwest. Children living in the areas with high aerosol acidity demonstrated more bronchitis and chest illness and lower lung function than children in clean areas. While asthma prevalence has been increasing in the past two decades, both the Six Cities and the Twenty-Four Cities Studies have shown no association between air pollution concentrations and the prevalence of asthma. On the other hand, in both studies, episodes of high air pollution have been associated with exacerbation of existing asthma.

An ongoing study (Five Cities Study) is assessing the degree to which minority and/or economically disadvantaged children are at increased risk for adverse respiratory health effects of ozone, acid aerosols and particulate air pollution. Inner-city poor and minority children appear to be at greater risk of respiratory illness, especially asthma. Previous studies (the Six and Twenty-Four Cities Studies) have demonstrated increased respiratory illness and lower lung function associated with air pollution among white children in suburban and rural communities. This study was designed to evaluate the risks among inner-city minority children for increased exposure to air pollutants (fine particles, acid aerosols and ozone) and the potential for increased sensitivity of inner-city children to air pollution as compared to white suburban children. Preliminary data from this study indicate that there were differences in sensitivity among the specific groups examined. Children living in the inner-city demonstrated a greater response to the same exposure than children in the suburbs. Black children showed a greater response than whites; girls more than boys, and children with hay fever more than those without allergies. All these differences suggest that genetic, socioeconomic, or housing characteristics may contribute to increased sensitivity to air pollution.

In the Spring of 1997, the US EPA proposed, then initiated changes in the National Ambient Air Quality Standards for particulate matter and ozone. The Harvard School of Public Health studies (along with a companion study by Pope, et al, entitled 'Particulate Air Pollution as a Predictor of Mortality in a Prospective Study of U.S. Adults') were the most significant among many that showed the association between particulate air pollution and adverse human health effects, such as mortality, and the aggravation of asthma and other chronic breathing disorders. While these studies are not without controversy, independent scientists from many different institutions have compiled a large body of epidemiological data showing increased mortality and morbidity associated with particulate air pollution in a wide range of cities around the world.

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